[PATCH v9 0/4] misc: fastrpc: Add polling mode support

[PATCH v9 0/4] misc: fastrpc: Add polling mode support

[Ekansh Gupta]

This patch series adds polling mode feature that have been missing in
upstream FastRPC driver.

- Add changes to move fdlist to ctx structure to avoid code duplicacy.
- Update context mask to support polling mode.
- Add changes to support polling feature.

Userspace change: https://github.com/qualcomm/fastrpc/pull/258
Patch [v8]: https://lore.kernel.org/all/20260415112530.4083240-1-ekansh.gupta@oss.qualcomm.com/

Changes in v9:
  - Added platform support check.
  - Moved to readl as per Luben's suggestion.
  - Cleaned up fastrpc_wait_for_completion().

Changes in v8:
  - Added more comments.

Changes in v7:
  - Fixed warnings.
  - Fixed commit text.
  - Addressed clean-up comments.

Changes in v6:
  - Fixed poll memory calculation.
  - Added few formatting changes.

Changes in v5:
  - Add more details in commit text.

Changes in v4:
  - Replace hardcoded ctxid mask with GENMASK.
  - Fixed commit text.

Changes in v3:
  - Resolve compilation warning.

Changes in v2:
  - Added comments and fixed commit text.
  - Defined context id position as a macro.
  - Added new IOCTL to control polling mode as always enabling
    it might cause excess power consumption.
  - Cleaned up polling mode implementation.

Ekansh Gupta (4):
  misc: fastrpc: Move fdlist to invoke context structure
  misc: fastrpc: Replace hardcoded ctxid mask with GENMASK
  misc: fastrpc: Expand context ID mask for DSP polling mode support
  misc: fastrpc: Add polling mode support for fastRPC driver

 drivers/misc/fastrpc.c      | 170 +++++++++++++++++++++++++++++++-----
 include/uapi/misc/fastrpc.h |  25 ++++++
 2 files changed, 175 insertions(+), 20 deletions(-)

-- 
2.34.1

[PATCH v9 1/4] misc: fastrpc: Move fdlist to invoke context structure

[Ekansh Gupta]

The fdlist is currently part of the meta buffer which is set during
fastrpc_get_args(), this fdlist is getting recalculated during
fastrpc_put_args().

Move fdlist to the invoke context structure to improve maintainability
and reduce redundancy. This centralizes its handling and simplifies
meta buffer preparation and reading logic.

Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
---
 drivers/misc/fastrpc.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 1080f9acf70a..a9f507a88c67 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -233,6 +233,7 @@ struct fastrpc_invoke_ctx {
 	int pid;
 	int client_id;
 	u32 sc;
+	u64 *fdlist;
 	u32 *crc;
 	u64 ctxid;
 	u64 msg_sz;
@@ -1016,6 +1017,7 @@ static int fastrpc_get_args(u32 kernel, struct fastrpc_invoke_ctx *ctx)
 	rpra = ctx->buf->virt;
 	list = fastrpc_invoke_buf_start(rpra, ctx->nscalars);
 	pages = fastrpc_phy_page_start(list, ctx->nscalars);
+	ctx->fdlist = (u64 *)(pages + ctx->nscalars);
 	args = (uintptr_t)ctx->buf->virt + metalen;
 	rlen = pkt_size - metalen;
 	ctx->rpra = rpra;
@@ -1118,18 +1120,11 @@ static int fastrpc_put_args(struct fastrpc_invoke_ctx *ctx,
 	union fastrpc_remote_arg *rpra = ctx->rpra;
 	struct fastrpc_user *fl = ctx->fl;
 	struct fastrpc_map *mmap = NULL;
-	struct fastrpc_invoke_buf *list;
-	struct fastrpc_phy_page *pages;
-	u64 *fdlist;
-	int i, inbufs, outbufs, handles;
+	u64 *fdlist = ctx->fdlist;
+	int i, inbufs;
 	int ret = 0;
 
 	inbufs = REMOTE_SCALARS_INBUFS(ctx->sc);
-	outbufs = REMOTE_SCALARS_OUTBUFS(ctx->sc);
-	handles = REMOTE_SCALARS_INHANDLES(ctx->sc) + REMOTE_SCALARS_OUTHANDLES(ctx->sc);
-	list = fastrpc_invoke_buf_start(rpra, ctx->nscalars);
-	pages = fastrpc_phy_page_start(list, ctx->nscalars);
-	fdlist = (uint64_t *)(pages + inbufs + outbufs + handles);
 
 	for (i = inbufs; i < ctx->nbufs; ++i) {
 		if (!ctx->maps[i]) {
-- 
2.34.1

Re: [PATCH v9 1/4] misc: fastrpc: Move fdlist to invoke context structure

[Dmitry Baryshkov]

On Wed, Apr 22, 2026 at 02:54:06PM +0530, Ekansh Gupta wrote:
> The fdlist is currently part of the meta buffer which is set during
> fastrpc_get_args(), this fdlist is getting recalculated during
> fastrpc_put_args().
> 
> Move fdlist to the invoke context structure to improve maintainability
> and reduce redundancy. This centralizes its handling and simplifies
> meta buffer preparation and reading logic.
> 
> Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
> ---
>  drivers/misc/fastrpc.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>


-- 
With best wishes
Dmitry

Claude review: misc: fastrpc: Move fdlist to invoke context structure

[Claude Code Review Bot]

Patch Review

**Assessment: Looks good with one minor observation.**

This patch moves the `fdlist` pointer from being recalculated in `fastrpc_put_args()` to being computed once in `fastrpc_get_args()` and stored in the context structure. This is a clean refactoring.

The original `fastrpc_put_args()` computed the fdlist as:
```c
fdlist = (uint64_t *)(pages + inbufs + outbufs + handles);
```
The new code in `fastrpc_get_args()` computes:
```c
ctx->fdlist = (u64 *)(pages + ctx->nscalars);
```

Since `ctx->nscalars = inbufs + outbufs + handles`, these are equivalent. The patch also removes `outbufs`, `handles`, `list`, and `pages` local variables from `fastrpc_put_args()` that are no longer needed.

**No issues found.**

---

---
Generated by Claude Code Patch Reviewer

[PATCH v9 2/4] misc: fastrpc: Replace hardcoded ctxid mask with GENMASK

[Ekansh Gupta]

Replace the hardcoded context ID mask (0xFF0) with GENMASK(11, 4) to
improve readability and follow kernel bitfield conventions. Use
FIELD_PREP and FIELD_GET instead of manual shifts for setting and
extracting ctxid values.

Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
---
 drivers/misc/fastrpc.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index a9f507a88c67..3f5d5d73be5a 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -23,6 +23,7 @@
 #include <uapi/misc/fastrpc.h>
 #include <linux/of_reserved_mem.h>
 #include <linux/bits.h>
+#include <linux/bitops.h>
 
 #define ADSP_DOMAIN_ID (0)
 #define MDSP_DOMAIN_ID (1)
@@ -37,7 +38,7 @@
 #define FASTRPC_CTX_MAX (256)
 #define FASTRPC_INIT_HANDLE	1
 #define FASTRPC_DSP_UTILITIES_HANDLE	2
-#define FASTRPC_CTXID_MASK (0xFF0)
+#define FASTRPC_CTXID_MASK GENMASK(11, 4)
 #define INIT_FILELEN_MAX (2 * 1024 * 1024)
 #define INIT_FILE_NAMELEN_MAX (128)
 #define FASTRPC_DEVICE_NAME	"fastrpc"
@@ -515,7 +516,7 @@ static void fastrpc_context_free(struct kref *ref)
 		fastrpc_buf_free(ctx->buf);
 
 	spin_lock_irqsave(&cctx->lock, flags);
-	idr_remove(&cctx->ctx_idr, ctx->ctxid >> 4);
+	idr_remove(&cctx->ctx_idr, FIELD_GET(FASTRPC_CTXID_MASK, ctx->ctxid));
 	spin_unlock_irqrestore(&cctx->lock, flags);
 
 	kfree(ctx->maps);
@@ -649,7 +650,7 @@ static struct fastrpc_invoke_ctx *fastrpc_context_alloc(
 		spin_unlock_irqrestore(&cctx->lock, flags);
 		goto err_idr;
 	}
-	ctx->ctxid = ret << 4;
+	ctx->ctxid = FIELD_PREP(FASTRPC_CTXID_MASK, ret);
 	spin_unlock_irqrestore(&cctx->lock, flags);
 
 	kref_init(&ctx->refcount);
@@ -2508,7 +2509,7 @@ static int fastrpc_rpmsg_callback(struct rpmsg_device *rpdev, void *data,
 	if (len < sizeof(*rsp))
 		return -EINVAL;
 
-	ctxid = ((rsp->ctx & FASTRPC_CTXID_MASK) >> 4);
+	ctxid = FIELD_GET(FASTRPC_CTXID_MASK, rsp->ctx);
 
 	spin_lock_irqsave(&cctx->lock, flags);
 	ctx = idr_find(&cctx->ctx_idr, ctxid);
-- 
2.34.1

Re: [PATCH v9 2/4] misc: fastrpc: Replace hardcoded ctxid mask with GENMASK

[Dmitry Baryshkov]

On Wed, Apr 22, 2026 at 02:54:07PM +0530, Ekansh Gupta wrote:
> Replace the hardcoded context ID mask (0xFF0) with GENMASK(11, 4) to
> improve readability and follow kernel bitfield conventions. Use
> FIELD_PREP and FIELD_GET instead of manual shifts for setting and
> extracting ctxid values.
> 
> Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
> Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
> ---
>  drivers/misc/fastrpc.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>


-- 
With best wishes
Dmitry

Claude review: misc: fastrpc: Replace hardcoded ctxid mask with GENMASK

[Claude Code Review Bot]

Patch Review

**Assessment: Clean improvement, no issues.**

Replaces `0xFF0` with `GENMASK(11, 4)` and converts manual shifts to `FIELD_PREP`/`FIELD_GET`. The three conversion sites are correct:

- `ctx->ctxid >> 4` becomes `FIELD_GET(FASTRPC_CTXID_MASK, ctx->ctxid)`
- `ret << 4` becomes `FIELD_PREP(FASTRPC_CTXID_MASK, ret)`
- `(rsp->ctx & FASTRPC_CTXID_MASK) >> 4` becomes `FIELD_GET(FASTRPC_CTXID_MASK, rsp->ctx)`

The `#include <linux/bitops.h>` is added but `FIELD_PREP`/`FIELD_GET` come from `<linux/bitfield.h>`. This would work only if `bitfield.h` is transitively included. Consider adding an explicit `#include <linux/bitfield.h>` instead.

Already has Konrad's Reviewed-by, which is appropriate.

---

---
Generated by Claude Code Patch Reviewer

[PATCH v9 3/4] misc: fastrpc: Expand context ID mask for DSP polling mode support

[Ekansh Gupta]

Current FastRPC context uses a 12-bit mask:
  [ID(8 bits)][PD type(4 bits)] = GENMASK(11, 4)

This works for normal calls but fails for DSP polling mode.
Polling mode expects a 16-bit layout:
  [15:8] = context ID (8 bits)
  [7:5]  = reserved
  [4]    = async mode bit
  [3:0]  = PD type (4 bits)

If async bit (bit 4) is set, DSP disables polling. With current
mask, odd IDs can set this bit, causing DSP to skip poll updates.

Update FASTRPC_CTXID_MASK to GENMASK(15, 8) so IDs occupy upper
byte and lower byte is left for DSP flags and PD type.

Reserved bits remain unused. This change is compatible with
polling mode and does not break non-polling behavior.

Bit layout:
  [15:8] = CCCCCCCC (context ID)
  [7:5]  = xxx (reserved)
  [4]    = A (async mode)
  [3:0]  = PPPP (PD type)

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
---
 drivers/misc/fastrpc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 3f5d5d73be5a..c4a3547a5c7f 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -38,7 +38,7 @@
 #define FASTRPC_CTX_MAX (256)
 #define FASTRPC_INIT_HANDLE	1
 #define FASTRPC_DSP_UTILITIES_HANDLE	2
-#define FASTRPC_CTXID_MASK GENMASK(11, 4)
+#define FASTRPC_CTXID_MASK GENMASK(15, 8)
 #define INIT_FILELEN_MAX (2 * 1024 * 1024)
 #define INIT_FILE_NAMELEN_MAX (128)
 #define FASTRPC_DEVICE_NAME	"fastrpc"
-- 
2.34.1

Claude review: misc: fastrpc: Expand context ID mask for DSP polling mode support

[Claude Code Review Bot]

Patch Review

**Assessment: Correct, well explained.**

Changes `GENMASK(11, 4)` to `GENMASK(15, 8)`. The commit message explains the bit layout clearly:
```
[15:8] = context ID (8 bits)
[7:5]  = reserved
[4]    = async mode bit
[3:0]  = PD type (4 bits)
```

This shifts the context ID up by 4 bits but the IDR still stores a compact integer and the mask handles packing/unpacking, so existing logic in `fastrpc_context_alloc`, `fastrpc_context_free`, and `fastrpc_rpmsg_callback` all continue to work correctly via `FIELD_PREP`/`FIELD_GET`.

**No issues found.** Has Dmitry's Reviewed-by.

---

---
Generated by Claude Code Patch Reviewer

[PATCH v9 4/4] misc: fastrpc: Add polling mode support for fastRPC driver

[Ekansh Gupta]

For any remote call to DSP, after sending an invocation message,
fastRPC driver waits for glink response and during this time the
CPU can go into low power modes. This adds latency to overall fastrpc
call as CPU wakeup and scheduling latencies are included. Add polling
mode support with which fastRPC driver will poll continuously on a
memory after sending a message to remote subsystem which will eliminate
CPU wakeup and scheduling latencies and reduce fastRPC overhead. In case
poll timeout happens, the call will fallback to normal RPC mode.  Poll
mode can be enabled by user by using FASTRPC_IOCTL_SET_OPTION ioctl
request with FASTRPC_POLL_MODE request id.

Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
---
 drivers/misc/fastrpc.c      | 148 ++++++++++++++++++++++++++++++++++--
 include/uapi/misc/fastrpc.h |  25 ++++++
 2 files changed, 166 insertions(+), 7 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index c4a3547a5c7f..7445e2aa3c3c 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -24,6 +24,8 @@
 #include <linux/of_reserved_mem.h>
 #include <linux/bits.h>
 #include <linux/bitops.h>
+#include <linux/compiler.h>
+#include <linux/iopoll.h>
 
 #define ADSP_DOMAIN_ID (0)
 #define MDSP_DOMAIN_ID (1)
@@ -38,6 +40,12 @@
 #define FASTRPC_CTX_MAX (256)
 #define FASTRPC_INIT_HANDLE	1
 #define FASTRPC_DSP_UTILITIES_HANDLE	2
+/*
+ * Maximum handle value for static handles.
+ * Static handles are pre-defined, fixed numeric values statically assigned
+ * in the IDL file or FastRPC framework.
+ */
+#define FASTRPC_MAX_STATIC_HANDLE (20)
 #define FASTRPC_CTXID_MASK GENMASK(15, 8)
 #define INIT_FILELEN_MAX (2 * 1024 * 1024)
 #define INIT_FILE_NAMELEN_MAX (128)
@@ -106,6 +114,12 @@
 
 #define miscdev_to_fdevice(d) container_of(d, struct fastrpc_device, miscdev)
 
+/* Poll response number from remote processor for call completion */
+#define FASTRPC_POLL_RESPONSE (0xdecaf)
+
+/* Polling mode timeout limit */
+#define FASTRPC_POLL_MAX_TIMEOUT_US (10000)
+
 struct fastrpc_phy_page {
 	dma_addr_t addr;	/* dma address */
 	u64 size;		/* size of contiguous region */
@@ -236,8 +250,14 @@ struct fastrpc_invoke_ctx {
 	u32 sc;
 	u64 *fdlist;
 	u32 *crc;
+	/* Poll memory that DSP updates */
+	u32 *poll_addr;
 	u64 ctxid;
 	u64 msg_sz;
+	/* work done status flag */
+	bool is_work_done;
+	/* process updates poll memory instead of glink response */
+	bool is_polled;
 	struct kref refcount;
 	struct list_head node; /* list of ctxs */
 	struct completion work;
@@ -263,6 +283,7 @@ struct fastrpc_soc_data {
 	u32 sid_pos;
 	u32 dma_addr_bits_cdsp;
 	u32 dma_addr_bits_default;
+	bool poll_mode_supported;
 };
 
 struct fastrpc_channel_ctx {
@@ -285,6 +306,7 @@ struct fastrpc_channel_ctx {
 	struct list_head invoke_interrupted_mmaps;
 	bool secure;
 	bool unsigned_support;
+	bool poll_mode_supported;
 	u64 dma_mask;
 	const struct fastrpc_soc_data *soc_data;
 };
@@ -308,6 +330,8 @@ struct fastrpc_user {
 	int client_id;
 	int pd;
 	bool is_secure_dev;
+	/* Flags poll mode state */
+	bool poll_mode;
 	/* Lock for lists */
 	spinlock_t lock;
 	/* lock for allocations */
@@ -923,7 +947,8 @@ static int fastrpc_get_meta_size(struct fastrpc_invoke_ctx *ctx)
 		sizeof(struct fastrpc_invoke_buf) +
 		sizeof(struct fastrpc_phy_page)) * ctx->nscalars +
 		sizeof(u64) * FASTRPC_MAX_FDLIST +
-		sizeof(u32) * FASTRPC_MAX_CRCLIST;
+		sizeof(u32) * FASTRPC_MAX_CRCLIST +
+		sizeof(u32);
 
 	return size;
 }
@@ -1019,6 +1044,9 @@ static int fastrpc_get_args(u32 kernel, struct fastrpc_invoke_ctx *ctx)
 	list = fastrpc_invoke_buf_start(rpra, ctx->nscalars);
 	pages = fastrpc_phy_page_start(list, ctx->nscalars);
 	ctx->fdlist = (u64 *)(pages + ctx->nscalars);
+	ctx->poll_addr = (u32 *)((uintptr_t)ctx->fdlist + sizeof(u64) * FASTRPC_MAX_FDLIST +
+			     sizeof(u32) * FASTRPC_MAX_CRCLIST);
+
 	args = (uintptr_t)ctx->buf->virt + metalen;
 	rlen = pkt_size - metalen;
 	ctx->rpra = rpra;
@@ -1188,6 +1216,61 @@ static int fastrpc_invoke_send(struct fastrpc_session_ctx *sctx,
 
 }
 
+static int poll_for_remote_response(struct fastrpc_invoke_ctx *ctx)
+{
+	u32 val;
+	int ret;
+
+	/*
+	 * Poll until DSP writes FASTRPC_POLL_RESPONSE into *ctx->poll_addr
+	 * or until another path marks the work done.
+	 */
+	ret = readl_poll_timeout_atomic(ctx->poll_addr, val,
+					(val == FASTRPC_POLL_RESPONSE) || ctx->is_work_done, 1,
+					FASTRPC_POLL_MAX_TIMEOUT_US);
+
+	if (!ret && val == FASTRPC_POLL_RESPONSE) {
+		ctx->is_work_done = true;
+		ctx->retval = 0;
+	}
+
+	if (ret == -ETIMEDOUT)
+		ret = -EIO;
+
+	return ret;
+}
+
+static inline int fastrpc_wait_for_response(struct fastrpc_invoke_ctx *ctx,
+					    u32 kernel)
+{
+	int err = 0;
+
+	if (kernel) {
+		if (!wait_for_completion_timeout(&ctx->work, 10 * HZ))
+			err = -ETIMEDOUT;
+	} else {
+		err = wait_for_completion_interruptible(&ctx->work);
+	}
+
+	return err;
+}
+
+static int fastrpc_wait_for_completion(struct fastrpc_invoke_ctx *ctx,
+				       u32 kernel)
+{
+	int err;
+
+	if (ctx->is_polled) {
+		err = poll_for_remote_response(ctx);
+		if (!err)
+			return 0;
+		/* If polling timed out or failed, move to normal response mode */
+		ctx->is_polled = false;
+	}
+
+	return fastrpc_wait_for_response(ctx, kernel);
+}
+
 static int fastrpc_internal_invoke(struct fastrpc_user *fl,  u32 kernel,
 				   u32 handle, u32 sc,
 				   struct fastrpc_invoke_args *args)
@@ -1223,13 +1306,14 @@ static int fastrpc_internal_invoke(struct fastrpc_user *fl,  u32 kernel,
 	if (err)
 		goto bail;
 
-	if (kernel) {
-		if (!wait_for_completion_timeout(&ctx->work, 10 * HZ))
-			err = -ETIMEDOUT;
-	} else {
-		err = wait_for_completion_interruptible(&ctx->work);
-	}
+	/*
+	 * Set message context as polled if the call is for a user PD
+	 * dynamic module and user has enabled poll mode.
+	 */
+	if (handle > FASTRPC_MAX_STATIC_HANDLE && fl->pd == USER_PD && fl->poll_mode)
+		ctx->is_polled = true;
 
+	err = fastrpc_wait_for_completion(ctx, kernel);
 	if (err)
 		goto bail;
 
@@ -1813,6 +1897,33 @@ static int fastrpc_get_info_from_kernel(struct fastrpc_ioctl_capability *cap,
 	return 0;
 }
 
+static int fastrpc_set_option(struct fastrpc_user *fl, char __user *argp)
+{
+	struct fastrpc_ioctl_set_option opt = {0};
+	int i;
+
+	if (copy_from_user(&opt, argp, sizeof(opt)))
+		return -EFAULT;
+
+	for (i = 0; i < ARRAY_SIZE(opt.reserved); i++) {
+		if (opt.reserved[i] != 0)
+			return -EINVAL;
+	}
+
+	if (opt.request_id != FASTRPC_POLL_MODE)
+		return -EINVAL;
+
+	if (opt.value) {
+		if (!fl->cctx->poll_mode_supported)
+			return -EOPNOTSUPP;
+		fl->poll_mode = true;
+	} else {
+		fl->poll_mode = false;
+	}
+
+	return 0;
+}
+
 static int fastrpc_get_dsp_info(struct fastrpc_user *fl, char __user *argp)
 {
 	struct fastrpc_ioctl_capability cap = {0};
@@ -2168,6 +2279,9 @@ static long fastrpc_device_ioctl(struct file *file, unsigned int cmd,
 	case FASTRPC_IOCTL_MEM_UNMAP:
 		err = fastrpc_req_mem_unmap(fl, argp);
 		break;
+	case FASTRPC_IOCTL_SET_OPTION:
+		err = fastrpc_set_option(fl, argp);
+		break;
 	case FASTRPC_IOCTL_GET_DSP_INFO:
 		err = fastrpc_get_dsp_info(fl, argp);
 		break;
@@ -2323,6 +2437,7 @@ static const struct fastrpc_soc_data kaanapali_soc_data = {
 	.sid_pos = 56,
 	.dma_addr_bits_cdsp = 34,
 	.dma_addr_bits_default = 32,
+	.poll_mode_supported = true,
 };
 
 static const struct fastrpc_soc_data default_soc_data = {
@@ -2331,6 +2446,22 @@ static const struct fastrpc_soc_data default_soc_data = {
 	.dma_addr_bits_default = 32,
 };
 
+/*
+ * Older platforms that use default_soc_data but whose DSP firmware
+ * supports the FastRPC polling mode.
+ */
+static const struct of_device_id fastrpc_poll_supported_machines[] __maybe_unused = {
+	{ .compatible = "qcom,qcs8300" },
+	{ .compatible = "qcom,qcs9100" },
+	{ .compatible = "qcom,sm8450" },
+	{ .compatible = "qcom,sm8550" },
+	{ .compatible = "qcom,sm8650" },
+	{ .compatible = "qcom,sm8750" },
+	{ .compatible = "qcom,x1e80100" },
+	{ .compatible = "qcom,x1p42100" },
+	{},
+};
+
 static int fastrpc_rpmsg_probe(struct rpmsg_device *rpdev)
 {
 	struct device *rdev = &rpdev->dev;
@@ -2397,6 +2528,8 @@ static int fastrpc_rpmsg_probe(struct rpmsg_device *rpdev)
 	secure_dsp = !(of_property_read_bool(rdev->of_node, "qcom,non-secure-domain"));
 	data->secure = secure_dsp;
 	data->soc_data = soc_data;
+	data->poll_mode_supported = soc_data->poll_mode_supported ||
+		of_machine_get_match(fastrpc_poll_supported_machines);
 
 	switch (domain_id) {
 	case ADSP_DOMAIN_ID:
@@ -2521,6 +2654,7 @@ static int fastrpc_rpmsg_callback(struct rpmsg_device *rpdev, void *data,
 	}
 
 	ctx->retval = rsp->retval;
+	ctx->is_work_done = true;
 	complete(&ctx->work);
 
 	/*
diff --git a/include/uapi/misc/fastrpc.h b/include/uapi/misc/fastrpc.h
index c6e2925f47e6..63346e27d5e9 100644
--- a/include/uapi/misc/fastrpc.h
+++ b/include/uapi/misc/fastrpc.h
@@ -16,6 +16,7 @@
 #define FASTRPC_IOCTL_INIT_CREATE_STATIC _IOWR('R', 9, struct fastrpc_init_create_static)
 #define FASTRPC_IOCTL_MEM_MAP		_IOWR('R', 10, struct fastrpc_mem_map)
 #define FASTRPC_IOCTL_MEM_UNMAP		_IOWR('R', 11, struct fastrpc_mem_unmap)
+#define FASTRPC_IOCTL_SET_OPTION	_IOWR('R', 12, struct fastrpc_ioctl_set_option)
 #define FASTRPC_IOCTL_GET_DSP_INFO	_IOWR('R', 13, struct fastrpc_ioctl_capability)
 
 /**
@@ -67,6 +68,24 @@ enum fastrpc_proc_attr {
 /* Fastrpc attribute for memory protection of buffers */
 #define FASTRPC_ATTR_SECUREMAP	(1)
 
+/**
+ * FASTRPC_POLL_MODE - Enable/disable poll mode for FastRPC invocations
+ *
+ * Poll mode is an optimization that allows the CPU to poll shared memory
+ * for completion instead of waiting for an interrupt-based response.
+ * This reduces latency for fast-completing operations.
+ *
+ * Restrictions:
+ * - Only supported for USER_PD (User Protection Domain)
+ * - Only applies to dynamic modules (handle > 20)
+ * - Static modules always use interrupt-based completion
+ *
+ * Values:
+ * - 0: Disable poll mode (use interrupt-based completion)
+ * - 1: Enable poll mode (poll shared memory for completion)
+ */
+#define FASTRPC_POLL_MODE	(1)
+
 struct fastrpc_invoke_args {
 	__u64 ptr;
 	__u64 length;
@@ -133,6 +152,12 @@ struct fastrpc_mem_unmap {
 	__s32 reserved[5];
 };
 
+struct fastrpc_ioctl_set_option {
+	__u32 request_id;	/* Request type (e.g., FASTRPC_POLL_MODE) */
+	__u32 value;	/* Request-specific value */
+	__s32 reserved[6];
+};
+
 struct fastrpc_ioctl_capability {
 	__u32 unused; /* deprecated, ignored by the kernel */
 	__u32 attribute_id;
-- 
2.34.1

Re: [PATCH v9 4/4] misc: fastrpc: Add polling mode support for fastRPC driver

[Dmitry Baryshkov]

On Wed, Apr 22, 2026 at 02:54:09PM +0530, Ekansh Gupta wrote:
> For any remote call to DSP, after sending an invocation message,
> fastRPC driver waits for glink response and during this time the
> CPU can go into low power modes. This adds latency to overall fastrpc
> call as CPU wakeup and scheduling latencies are included. Add polling
> mode support with which fastRPC driver will poll continuously on a
> memory after sending a message to remote subsystem which will eliminate
> CPU wakeup and scheduling latencies and reduce fastRPC overhead. In case
> poll timeout happens, the call will fallback to normal RPC mode.  Poll
> mode can be enabled by user by using FASTRPC_IOCTL_SET_OPTION ioctl
> request with FASTRPC_POLL_MODE request id.
> 
> Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
> ---
>  drivers/misc/fastrpc.c      | 148 ++++++++++++++++++++++++++++++++++--
>  include/uapi/misc/fastrpc.h |  25 ++++++
>  2 files changed, 166 insertions(+), 7 deletions(-)
> 
> @@ -2331,6 +2446,22 @@ static const struct fastrpc_soc_data default_soc_data = {
>  	.dma_addr_bits_default = 32,
>  };
>  
> +/*
> + * Older platforms that use default_soc_data but whose DSP firmware
> + * supports the FastRPC polling mode.

There should be a comment, "don't add more platforms to this list".

> + */
> +static const struct of_device_id fastrpc_poll_supported_machines[] __maybe_unused = {
> +	{ .compatible = "qcom,qcs8300" },
> +	{ .compatible = "qcom,qcs9100" },

Use qcom,sa8775p instead. See sa8775p-ride boards.
What about qcom,sar2130p?
qcom,sc8280xp?
qcom,milos?

> +	{ .compatible = "qcom,sm8450" },
> +	{ .compatible = "qcom,sm8550" },
> +	{ .compatible = "qcom,sm8650" },
> +	{ .compatible = "qcom,sm8750" },
> +	{ .compatible = "qcom,x1e80100" },
> +	{ .compatible = "qcom,x1p42100" },
> +	{},
> +};
> +
>  static int fastrpc_rpmsg_probe(struct rpmsg_device *rpdev)
>  {
>  	struct device *rdev = &rpdev->dev;

-- 
With best wishes
Dmitry

Claude review: misc: fastrpc: Add polling mode support for fastRPC driver

[Claude Code Review Bot]

Patch Review

**Assessment: Has several issues that need addressing.**

**Issue 1 (Build break): `of_machine_get_match` does not exist**

```c
data->poll_mode_supported = soc_data->poll_mode_supported ||
    of_machine_get_match(fastrpc_poll_supported_machines);
```

The kernel has `of_machine_device_match()` (returns `bool`) and `of_machine_get_match_data()` (returns `const void *`). Since you only need a boolean "is this machine in the list", use `of_machine_device_match()`:

```c
data->poll_mode_supported = soc_data->poll_mode_supported ||
    of_machine_device_match(fastrpc_poll_supported_machines);
```

**Issue 2: `readl_poll_timeout_atomic` on DMA buffer memory**

```c
ret = readl_poll_timeout_atomic(ctx->poll_addr, val,
                (val == FASTRPC_POLL_RESPONSE) || ctx->is_work_done, 1,
                FASTRPC_POLL_MAX_TIMEOUT_US);
```

`ctx->poll_addr` points into `ctx->buf->virt`, which is a DMA coherent buffer allocated via `dma_alloc_coherent()`, not an MMIO register. `readl()` is intended for MMIO and may apply `__iomem` annotations or arch-specific I/O accessors that are inappropriate for regular memory.

Use `read_poll_timeout(READ_ONCE, ...)` or a custom polling loop with `READ_ONCE()` instead. This also avoids the atomic context restriction (see Issue 3).

**Issue 3: 10ms atomic busy-wait**

`readl_poll_timeout_atomic` uses `udelay()` and disables preemption for the entire duration. With `FASTRPC_POLL_MAX_TIMEOUT_US = 10000` (10ms), this is a very long time to hold a CPU non-preemptible. The non-atomic variant (`readl_poll_timeout` / `read_poll_timeout`) uses `usleep_range()` which is much more scheduler-friendly, and this code path is in process context (ioctl handler), so sleeping is fine.

**Issue 4: Data race on `ctx->is_work_done`**

`ctx->is_work_done` is read in the polling condition and written from `fastrpc_rpmsg_callback` (interrupt context) without any synchronization:

```c
// In poll_for_remote_response (process context):
(val == FASTRPC_POLL_RESPONSE) || ctx->is_work_done

// In fastrpc_rpmsg_callback (interrupt context):
ctx->is_work_done = true;
```

A plain `bool` is not guaranteed to be atomically visible across CPUs. This should use `READ_ONCE(ctx->is_work_done)` in the polling condition and `WRITE_ONCE(ctx->is_work_done, true)` in the callback (or use an atomic flag).

Similarly in `poll_for_remote_response`:
```c
if (!ret && val == FASTRPC_POLL_RESPONSE) {
    ctx->is_work_done = true;
```
This write should also use `WRITE_ONCE`.

**Issue 5: `ctx->retval = 0` in poll path may race with callback**

In `poll_for_remote_response`:
```c
if (!ret && val == FASTRPC_POLL_RESPONSE) {
    ctx->is_work_done = true;
    ctx->retval = 0;
}
```

The callback also sets `ctx->retval = rsp->retval`. If the DSP writes the poll response *and* sends an rpmsg response, both paths could write `retval` concurrently. The poll path hardcodes `retval = 0`, which may not match the actual DSP return value. If the DSP puts the real return value in the rpmsg response, blindly setting it to 0 in the poll path loses error information.

**Issue 6: Missing `dma_rmb()` after polling**

The existing code has a `dma_rmb()` barrier between receiving the completion and calling `fastrpc_put_args()`:
```c
/* make sure that all memory writes by DSP are seen by CPU */
dma_rmb();
```

After the polling path succeeds, the same barrier is needed to ensure the CPU sees all DSP writes to the output buffers. The current code does fall through to `fastrpc_put_args()` after `fastrpc_wait_for_completion()` returns, but the `dma_rmb()` is placed after the original wait code. Verify the barrier is still hit on the polling-success path — looking at the patched flow, `fastrpc_wait_for_completion()` returns 0, then execution continues to the existing `dma_rmb()` + `fastrpc_put_args()`, so this should be fine.

**Issue 7: `__maybe_unused` on the match table**

```c
static const struct of_device_id fastrpc_poll_supported_machines[] __maybe_unused = {
```

This suggests it may be unused when `CONFIG_OF` is off. But `of_machine_device_match()` has a stub returning `false` when `!CONFIG_OF`, so the table would indeed be unused. A cleaner approach would be to wrap the call with `IS_ENABLED(CONFIG_OF)` or just accept that this driver practically requires OF.

**Issue 8: IOCTL number 12 skipped for `SET_OPTION`**

The existing header has ioctl numbers 1-11 and then 13. The new `FASTRPC_IOCTL_SET_OPTION` is assigned number 12, which fills the gap. This is fine and intentional.

**Issue 9: `FASTRPC_POLL_MODE` value documentation says "handle > 20" but code uses `FASTRPC_MAX_STATIC_HANDLE`**

The UAPI header comment says:
```c
 * - Only applies to dynamic modules (handle > 20)
```

And the code uses:
```c
if (handle > FASTRPC_MAX_STATIC_HANDLE && ...)
```

Where `FASTRPC_MAX_STATIC_HANDLE` is defined as 20. This is consistent, but hardcoding "20" in the UAPI comment is fragile. Consider referencing the macro name instead.

**Minor: `fastrpc_wait_for_response` is marked `inline`**

```c
static inline int fastrpc_wait_for_response(...)
```

The `inline` keyword is unnecessary — the compiler will decide. Kernel style generally avoids explicit `inline` on static functions unless there's a specific reason.

---
Generated by Claude Code Patch Reviewer

Claude review: misc: fastrpc: Add polling mode support

[Claude Code Review Bot]

Overall Series Review

Subject: misc: fastrpc: Add polling mode support
Author: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
Patches: 8
Reviewed: 2026-04-23T07:50:44.016413

---

This is a v9 series adding DSP polling mode support to the FastRPC driver. The series is logically structured: patch 1 is a minor refactor, patch 2 converts to GENMASK/FIELD_GET, patch 3 expands the context ID mask, and patch 4 adds the polling mode feature itself.

**Key concerns:**
1. **Build-breaking bug in patch 4**: The function `of_machine_get_match()` does not exist in the kernel. The correct API is `of_machine_device_match()` (returns `bool`). This will cause a compilation failure.
2. **`readl_poll_timeout_atomic` on non-MMIO memory**: `readl()` is for memory-mapped I/O registers. The poll address is DMA coherent buffer memory (from `fastrpc_buf`). Using `readl()` on regular RAM is semantically wrong. A simple `READ_ONCE()` loop or `read_poll_timeout` with `READ_ONCE` would be more appropriate.
3. **Atomic busy-wait for 10ms**: `readl_poll_timeout_atomic` uses `udelay()`, holding the CPU in a tight busy loop for up to 10ms. This is a long time to disable preemption. The non-atomic `readl_poll_timeout` (which uses `usleep_range`) would be much better given this isn't an atomic context.
4. **Missing `__maybe_unused` justification**: The `fastrpc_poll_supported_machines` table is marked `__maybe_unused` which suppresses a warning when `CONFIG_OF` is disabled, but the driver already depends on OF via rpmsg/qcom infrastructure. This feels like papering over a warning rather than addressing it properly.

Overall the approach is reasonable but needs the compilation fix and the polling mechanism reviewed for correctness.

---

---
Generated by Claude Code Patch Reviewer

[PATCH v6 0/4] misc: fastrpc: Add polling mode support

[Ekansh Gupta]

This patch series adds polling mode feature that have been missing in
upstream FastRPC driver.

- Add changes to move fdlist to ctx structure to avoid code duplicacy.
- Update context mask to support polling mode.
- Add changes to support polling feature.

Userspace change: https://github.com/qualcomm/fastrpc/pull/258
Patch [v5]: https://lore.kernel.org/all/20251230062831.1195116-1-ekansh.gupta@oss.qualcomm.com/

Changes in v5:
  - Fixed poll memory calculation.
  - Added few formatting changes.

Changes in v5:
  - Add more details in commit text.

Changes in v4:
  - Replace hardcoded ctxid mask with GENMASK.
  - Fixed commit text.

Changes in v3:
  - Resolve compilation warning.

Changes in v2:
  - Added comments and fixed commit text.
  - Defined context id position as a macro.
  - Added new IOCTL to control polling mode as always enabling
    it might cause excess power consumption.
  - Cleaned up polling mode implementation.

Ekansh Gupta (4):
  misc: fastrpc: Move fdlist to invoke context structure
  misc: fastrpc: Replace hardcoded ctxid mask with GENMASK
  misc: fastrpc: Expand context ID mask for DSP polling mode support
  misc: fastrpc: Add polling mode support for fastRPC driver

 drivers/misc/fastrpc.c      | 166 +++++++++++++++++++++++++++++++-----
 include/uapi/misc/fastrpc.h |  10 +++
 2 files changed, 154 insertions(+), 22 deletions(-)

-- 
2.34.1

Claude review: misc: fastrpc: Add polling mode support

[Claude Code Review Bot]

Overall Series Review

Subject: misc: fastrpc: Add polling mode support
Author: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
Patches: 5
Reviewed: 2026-02-16T06:40:36.401669

---



---
Generated by Claude Code Patch Reviewer