Re: [PATCH v2 15/15] accel/qda: Add remote memory unmap from DSP address space

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

On 17-08-2026 11:14, Dmitry Baryshkov wrote:
> On Mon, Aug 17, 2026 at 10:38:45AM +0530, Ekansh Gupta wrote:
>> Add DRM_IOCTL_QDA_REMOTE_MUNMAP, which removes a mapping previously
>> established with DRM_IOCTL_QDA_REMOTE_MAP from the DSP address space of
>> the calling process.
>>
>> Mirroring the map path, the DSP exposes two unmap operations, both
>> reachable through this IOCTL and selected by the request field of
>> struct drm_qda_mem_unmap:
>>
>>   QDA_REQUEST_MUNMAP unmaps a region by the DSP address that the
>>   corresponding map call returned. It uses the vaddrout and size fields.
>>
>>   QDA_REQUEST_MEM_UNMAP unmaps a region by buffer identity, using the
>>   GEM handle, the DSP virtual address and the size.
> 
> Why do we need two different operations? Can you just pass the GEM
> handle to the IOCTL?
QDA_REQUEST_MUNMAP (RMID 5): The DSP locates the mapping by the DSP
virtual address that was returned by the corresponding MMAP call. This
is the older protocol message that only needs {address, size} to
identify the region in the DSP's page table.

QDA_REQUEST_MEM_UNMAP (RMID 11): The DSP locates the mapping by its
internal handle association. This is the newer protocol message that is
not supported on older platforms.

> 
> Also, what happens if the buffer is still in use on the DSP side? Will
> the DSP crash? Will the whole board crash?
The access from DSP after unmap will trigger an SMMU context fault on
the context bank device. The fault does not bring down the board but
might trigger remoteproc to restart(I'm not exactly sure about the iommu
side handling of such faults).

Thanks for reviewing the patches.

//Ekansh

> 
> 
>>
>> Each request type has its own argument builder in qda_fastrpc.c,
>> documented with the packed argument layout the DSP expects. Unknown
>> request types are rejected with -EINVAL.
>>
>> Assisted-by: Claude:claude-sonnet-5
>> Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
>> ---
>>  drivers/accel/qda/qda_drv.c     |   1 +
>>  drivers/accel/qda/qda_fastrpc.c | 119 ++++++++++++++++++++++++++++++++++++++++
>>  drivers/accel/qda/qda_fastrpc.h |  34 ++++++++++++
>>  drivers/accel/qda/qda_ioctl.c   |  22 ++++++++
>>  drivers/accel/qda/qda_ioctl.h   |   1 +
>>  include/uapi/drm/qda_accel.h    |  39 ++++++++++++-
>>  6 files changed, 215 insertions(+), 1 deletion(-)
>>
>>
>