Re: [PATCH RFC 05/18] accel/qda: Create compute CB devices on QDA compute bus

[Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>]

On Thu, Feb 26, 2026 at 02:08:57PM +0530, Ekansh Gupta wrote:
> 
> 
> On 2/24/2026 4:19 AM, Dmitry Baryshkov wrote:
> > On Tue, Feb 24, 2026 at 12:38:59AM +0530, Ekansh Gupta wrote:
> >> Add support for creating compute context-bank (CB) devices under
> >> the QDA compute bus based on child nodes of the FastRPC RPMsg
> >> device tree node. Each DT child with compatible
> >> "qcom,fastrpc-compute-cb" is turned into a QDA-owned struct
> >> device on qda_cb_bus_type.
> >>
> >> A new qda_cb_dev structure and cb_devs list in qda_dev track these
> >> CB devices. qda_populate_child_devices() walks the DT children
> >> during QDA RPMsg probe, creates CB devices, configures their DMA
> >> and IOMMU settings using of_dma_configure(), and associates a SID
> >> from the "reg" property when present.
> >>
> >> On RPMsg remove, qda_unpopulate_child_devices() tears down all CB
> >> devices, removing them from their IOMMU groups if present and
> >> unregistering the devices. This prepares the ground for using CB
> >> devices as IOMMU endpoints for DSP compute workloads in later
> >> patches.
> > Are we loosing the nsessions support?
> Yes, it's not part of this series. I'll try bringing that as well.
> >
> >> Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
> >> ---
> >>  drivers/accel/qda/Makefile    |   1 +
> >>  drivers/accel/qda/qda_cb.c    | 150 ++++++++++++++++++++++++++++++++++++++++++
> >>  drivers/accel/qda/qda_cb.h    |  26 ++++++++
> >>  drivers/accel/qda/qda_drv.h   |   3 +
> >>  drivers/accel/qda/qda_rpmsg.c |  40 +++++++++++
> >>  5 files changed, 220 insertions(+)
> >>
> >> diff --git a/drivers/accel/qda/Makefile b/drivers/accel/qda/Makefile
> >> index 242684ef1af7..4aded20b6bc2 100644
> >> --- a/drivers/accel/qda/Makefile
> >> +++ b/drivers/accel/qda/Makefile
> >> @@ -8,5 +8,6 @@ obj-$(CONFIG_DRM_ACCEL_QDA)	:= qda.o
> >>  qda-y := \
> >>  	qda_drv.o \
> >>  	qda_rpmsg.o \
> >> +	qda_cb.o \
> >>  
> >>  obj-$(CONFIG_DRM_ACCEL_QDA_COMPUTE_BUS) += qda_compute_bus.o
> >> diff --git a/drivers/accel/qda/qda_cb.c b/drivers/accel/qda/qda_cb.c
> >> new file mode 100644
> >> index 000000000000..77a2d8cae076
> >> --- /dev/null
> >> +++ b/drivers/accel/qda/qda_cb.c
> >> @@ -0,0 +1,150 @@
> >> +// SPDX-License-Identifier: GPL-2.0-only
> >> +// Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
> >> +#include <linux/dma-mapping.h>
> >> +#include <linux/device.h>
> >> +#include <linux/of.h>
> >> +#include <linux/of_device.h>
> >> +#include <linux/iommu.h>
> >> +#include <linux/slab.h>
> >> +#include "qda_drv.h"
> >> +#include "qda_cb.h"
> >> +
> >> +static void qda_cb_dev_release(struct device *dev)
> >> +{
> >> +	kfree(dev);
> > Do you need to put the reference on the OF node?
> Reference put is happening as part of qda_destroy_cb_device.

This way: you have a (small) window where of_node is already put (and
might be gone), but the pointer is not NULL. The of_node should be put
only when device is no longer accessible from the rest of the system, in
release function.


-- 
With best wishes
Dmitry