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

[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

[PATCH v6 1/4] misc: fastrpc: Move fdlist to invoke context structure

[Ekansh Gupta]

The fdlist is currently part of the meta buffer, computed during
put_args. This leads to code duplication when preparing and reading
critical meta buffer contents used by the FastRPC driver.

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 | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 4f5a79c50f58..ce397c687161 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;
@@ -1018,6 +1019,7 @@ 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;
@@ -1120,18 +1122,10 @@ 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;
+	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]) {
@@ -1153,9 +1147,9 @@ static int fastrpc_put_args(struct fastrpc_invoke_ctx *ctx,
 cleanup_fdlist:
 	/* Clean up fdlist which is updated by DSP */
 	for (i = 0; i < FASTRPC_MAX_FDLIST; i++) {
-		if (!fdlist[i])
+		if (!ctx->fdlist[i])
 			break;
-		if (!fastrpc_map_lookup(fl, (int)fdlist[i], &mmap))
+		if (!fastrpc_map_lookup(fl, (int)ctx->fdlist[i], &mmap))
 			fastrpc_map_put(mmap);
 	}
 
-- 
2.34.1

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

[Claude Code Review Bot]

Patch Review

**Assessment: Acceptable with minor comments**

This is a clean refactoring patch. Moving `fdlist` into `fastrpc_invoke_ctx` eliminates the redundant pointer computation in `fastrpc_put_args`.

One concern: In the original `fastrpc_put_args`, the fdlist pointer was computed using the actual scalar breakdown:

```c
fdlist = (uint64_t *)(pages + inbufs + outbufs + handles);
```

In `fastrpc_get_args`, it's now computed as:

```c
ctx->fdlist = (u64 *)(pages + ctx->nscalars);
```

Since `nscalars = inbufs + outbufs + REMOTE_SCALARS_INHANDLES(sc) + REMOTE_SCALARS_OUTHANDLES(sc)`, which equals `inbufs + outbufs + handles`, these are equivalent. This is correct.

The removal of the now-unused `outbufs`, `handles`, `list`, `pages` local variables from `fastrpc_put_args` is appropriate.

---
Generated by Claude Code Patch Reviewer

[PATCH v6 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 | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index ce397c687161..0d8d89a2e220 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -37,7 +37,7 @@
 #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 +515,7 @@ 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);
@@ -651,7 +651,7 @@ 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);
@@ -2506,7 +2506,7 @@ 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

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

[Claude Code Review Bot]

Patch Review

**Assessment: Good, straightforward cleanup**

This patch is a clean mechanical replacement of `0xFF0` with `GENMASK(11, 4)` and manual shift operations with `FIELD_PREP`/`FIELD_GET`. The semantics are preserved exactly:

- `ctx->ctxid = ret << 4` becomes `ctx->ctxid = FIELD_PREP(FASTRPC_CTXID_MASK, ret)` — equivalent for `GENMASK(11, 4)`.
- `idr_remove(&cctx->ctx_idr, ctx->ctxid >> 4)` becomes `idr_remove(&cctx->ctx_idr, FIELD_GET(FASTRPC_CTXID_MASK, ctx->ctxid))` — equivalent.
- `((rsp->ctx & FASTRPC_CTXID_MASK) >> 4)` becomes `FIELD_GET(FASTRPC_CTXID_MASK, rsp->ctx)` — equivalent.

Already has Reviewed-by from Konrad Dybcio.

---
Generated by Claude Code Patch Reviewer

[PATCH v6 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 0d8d89a2e220..e935ae3776b4 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -37,7 +37,7 @@
 #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: Acceptable, good commit message**

The commit message provides a clear explanation of the bit layout change:
```
[15:8] = CCCCCCCC (context ID)
[7:5]  = xxx (reserved)
[4]    = A (async mode)
[3:0]  = PPPP (PD type)
```

Changing `GENMASK(11, 4)` to `GENMASK(15, 8)` shifts the context ID into the upper byte, leaving the lower byte for DSP flags. Because patch 2 already converted everything to use `FIELD_PREP`/`FIELD_GET` with the symbolic mask, this is a one-line change. Clean and correct.

Already has Reviewed-by from Dmitry Baryshkov.

---
Generated by Claude Code Patch Reviewer

[PATCH v6 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. 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      | 142 ++++++++++++++++++++++++++++++++++--
 include/uapi/misc/fastrpc.h |  10 +++
 2 files changed, 145 insertions(+), 7 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index e935ae3776b4..c1e67dbacf2c 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -23,6 +23,8 @@
 #include <uapi/misc/fastrpc.h>
 #include <linux/of_reserved_mem.h>
 #include <linux/bits.h>
+#include <linux/compiler.h>
+#include <linux/iopoll.h>
 
 #define ADSP_DOMAIN_ID (0)
 #define MDSP_DOMAIN_ID (1)
@@ -37,6 +39,7 @@
 #define FASTRPC_CTX_MAX (256)
 #define FASTRPC_INIT_HANDLE	1
 #define FASTRPC_DSP_UTILITIES_HANDLE	2
+#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)
@@ -105,6 +108,12 @@
 
 #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 */
@@ -235,8 +244,14 @@ struct fastrpc_invoke_ctx {
 	u32 sc;
 	u64 *fdlist;
 	u32 *crc;
+	/* Poll memory that DSP updates */
+	u32 *poll;
 	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;
@@ -307,6 +322,8 @@ 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 */
@@ -924,7 +941,8 @@ 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;
 }
@@ -1020,6 +1038,9 @@ 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 = (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 +1209,75 @@ static int fastrpc_invoke_send(struct fastrpc_session_ctx *sctx,
 
 }
 
+static inline u32 fastrpc_poll_op(void *p)
+{
+	struct fastrpc_invoke_ctx *ctx = p;
+
+	dma_rmb();
+	return READ_ONCE(*ctx->poll);
+}
+
+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
+	 * or until another path marks the work done.
+	 */
+	ret = read_poll_timeout_atomic(fastrpc_poll_op, val,
+				       (val == FASTRPC_POLL_RESPONSE) ||
+				       ctx->is_work_done, 1,
+				       FASTRPC_POLL_MAX_TIMEOUT_US, false, ctx);
+
+	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;
+
+	do {
+		if (ctx->is_polled) {
+			err = poll_for_remote_response(ctx);
+			/* If polling timed out, move to normal response mode */
+			if (err)
+				ctx->is_polled = false;
+		} else {
+			err = fastrpc_wait_for_response(ctx, kernel);
+			if (err)
+				return err;
+		}
+	} while (!ctx->is_work_done);
+
+	return err;
+}
+
 static int fastrpc_internal_invoke(struct fastrpc_user *fl,  u32 kernel,
 				   u32 handle, u32 sc,
 				   struct fastrpc_invoke_args *args)
@@ -1223,16 +1313,26 @@ 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;
 
+	if (!ctx->is_work_done) {
+		err = -ETIMEDOUT;
+		dev_dbg(fl->sctx->dev, "Invalid workdone state for handle 0x%x, sc 0x%x\n",
+			handle, sc);
+		goto bail;
+	}
+
 	/* make sure that all memory writes by DSP are seen by CPU */
 	dma_rmb();
 	/* populate all the output buffers with results */
@@ -1812,6 +1912,30 @@ 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.req != FASTRPC_POLL_MODE)
+		return -EINVAL;
+
+	if (opt.value)
+		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};
@@ -2167,6 +2291,9 @@ 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;
@@ -2518,6 +2645,7 @@ 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..c37e24a764ae 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 +68,9 @@ enum fastrpc_proc_attr {
 /* Fastrpc attribute for memory protection of buffers */
 #define FASTRPC_ATTR_SECUREMAP	(1)
 
+/* Set option request ID to enable poll mode */
+#define FASTRPC_POLL_MODE	(1)
+
 struct fastrpc_invoke_args {
 	__u64 ptr;
 	__u64 length;
@@ -133,6 +137,12 @@ struct fastrpc_mem_unmap {
 	__s32 reserved[5];
 };
 
+struct fastrpc_ioctl_set_option {
+	__u32 req;	/* request id */
+	__u32 value;	/* value */
+	__s32 reserved[6];
+};
+
 struct fastrpc_ioctl_capability {
 	__u32 unused; /* deprecated, ignored by the kernel */
 	__u32 attribute_id;
-- 
2.34.1

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

[Claude Code Review Bot]

Patch Review

**Assessment: Needs revision — several issues**

**Issue 1 — Race condition on `is_work_done` and `retval`**

`ctx->is_work_done` is set to `true` in two places without any locking or atomic operations:

```c
// In poll_for_remote_response():
ctx->is_work_done = true;
ctx->retval = 0;

// In fastrpc_rpmsg_callback():
ctx->retval = rsp->retval;
ctx->is_work_done = true;
complete(&ctx->work);
```

If the DSP writes the poll response and the rpmsg callback fires concurrently, both paths could race. The rpmsg callback sets `ctx->retval = rsp->retval` while the poll path sets `ctx->retval = 0`, potentially clobbering the actual return value. Consider using `atomic_t` or `smp_store_release`/`smp_load_acquire` for `is_work_done`, and not overwriting `retval` in the poll path if the callback has already set it.

**Issue 2 — Error propagation in `fastrpc_wait_for_completion`**

```c
do {
    if (ctx->is_polled) {
        err = poll_for_remote_response(ctx);
        if (err)
            ctx->is_polled = false;
    } else {
        err = fastrpc_wait_for_response(ctx, kernel);
        if (err)
            return err;
    }
} while (!ctx->is_work_done);

return err;
```

When polling times out, `err` is set to `-EIO`, `is_polled` is set to `false`, and the loop continues. On the next iteration, `fastrpc_wait_for_response` succeeds (returns 0), `is_work_done` becomes true, and the loop exits. But `err` is still `-EIO` from the polling iteration. This means `err` is not cleared on success in the wait path — the return at the end returns the stale `-EIO`. This needs to be fixed, either by resetting `err = 0` after a successful `fastrpc_wait_for_response`, or by restructuring the loop.

**Issue 3 — `poll_for_remote_response` maps `-ETIMEDOUT` to `-EIO`**

```c
if (ret == -ETIMEDOUT)
    ret = -EIO;
```

The intent seems to be that `-ETIMEDOUT` from `read_poll_timeout_atomic` shouldn't propagate as a timeout (since it's an expected transition to interrupt-based waiting). But the function returns `-EIO` on timeout, which is misleading. The caller (`fastrpc_wait_for_completion`) treats any non-zero return as "switch to interrupt mode". Consider just returning `-ETIMEDOUT` directly and handling it in the caller, or returning 0 if the design intent is "polling timed out, fall through to interrupt."

**Issue 4 — UAPI: `_IOWR` vs `_IOW`**

```c
#define FASTRPC_IOCTL_SET_OPTION	_IOWR('R', 12, struct fastrpc_ioctl_set_option)
```

The kernel only calls `copy_from_user` on this ioctl — it never copies data back to userspace. This should be `_IOW`, not `_IOWR`. Using `_IOWR` implies bidirectional data transfer. Since this is a UAPI change, it should be fixed before merging.

**Issue 5 — `fastrpc_poll_op` barrier placement**

```c
static inline u32 fastrpc_poll_op(void *p)
{
    struct fastrpc_invoke_ctx *ctx = p;
    dma_rmb();
    return READ_ONCE(*ctx->poll);
}
```

The `dma_rmb()` is placed *before* `READ_ONCE(*ctx->poll)`. A read memory barrier orders prior reads before subsequent reads. Here the intent is presumably to ensure that after seeing the poll response, subsequent reads (of output buffers) see the DSP's writes. But the barrier should be *after* the read of the poll word for that purpose, not before. The current placement ensures nothing useful — there's no prior DMA read to order against. Consider moving the `dma_rmb()` to after the poll value is observed to equal `FASTRPC_POLL_RESPONSE`, or into the caller after poll success.

**Issue 6 — `FASTRPC_MAX_STATIC_HANDLE` is a new constant without clear justification**

```c
#define FASTRPC_MAX_STATIC_HANDLE (20)
```

The patch adds this and uses it to restrict polling to dynamic handles:
```c
if (handle > FASTRPC_MAX_STATIC_HANDLE && fl->pd == USER_PD &&
    fl->poll_mode)
```

The value 20 appears to be a convention from the DSP side. A comment explaining what "static handles" are and why polling shouldn't apply to them would help maintainability.

**Issue 7 — `fastrpc_set_option` style**

```c
if (opt.value)
    fl->poll_mode = true;
else
    fl->poll_mode = false;
```

This can be simplified to:
```c
fl->poll_mode = !!opt.value;
```

**Issue 8 — Missing `__user` annotation correctness**

```c
static int fastrpc_set_option(struct fastrpc_user *fl, char __user *argp)
```

The function parameter is `char __user *argp` but it's passed to `copy_from_user` as the source for a `struct fastrpc_ioctl_set_option`. This works but would be cleaner as `void __user *argp` to match the other ioctl handlers in this file (checking existing style).

**Issue 9 — Poll memory size accounting**

The meta buffer size is increased by `sizeof(u32)` (4 bytes) for the poll word:

```c
sizeof(u32) * FASTRPC_MAX_CRCLIST +
sizeof(u32);
```

And the poll pointer is computed as:

```c
ctx->poll = (u32 *)((uintptr_t)ctx->fdlist + sizeof(u64) * FASTRPC_MAX_FDLIST +
                     sizeof(u32) * FASTRPC_MAX_CRCLIST);
```

This skips past fdlist (16 × 8 = 128 bytes) and crclist (64 × 4 = 256 bytes). But `ctx->fdlist` is at `(pages + ctx->nscalars)`, and `ctx->crc` is not explicitly computed here. Comparing with the meta size calculation, the layout is: rpra | invoke_bufs | phy_pages | fdlist | crclist | poll_word. The computation looks correct, but note that `ctx->crc` pointer from the original code is stored in the struct but never set in this patch series. The `crc` field initialization should be verified for correctness.

---
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: 5
Reviewed: 2026-02-16T06:40:36.401669

---



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Generated by Claude Code Patch Reviewer