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

[Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>]

On 2/26/2026 4:16 PM, Dmitry Baryshkov wrote:
> 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.
I'll move put to release function to avoid suggested scenario. Thanks.
>
>