Re: [PATCH RFC 03/13] drm/msm: look for lpac from dts

[Akhil P Oommen <akhilpo@oss.qualcomm.com>]

On 7/7/2026 10:09 PM, Dmitry Baryshkov wrote:
> On Tue, Jul 07, 2026 at 05:02:43PM +0200, Anna Maniscalco wrote:
>> On 7/6/26 5:04 PM, Dmitry Baryshkov wrote:
>>> On Sun, Jul 05, 2026 at 09:13:37PM +0200, Anna Maniscalco wrote:
>>>> In order to associate the SID used by LPAC to it's own domain and
>>>> context bank we need a separate node on the DTS.
>>> Can we use iommu-map instead of adding a new device using the same
>>> addresses? You provide zero explanations, but it seems like you are
>>> trying to separate a part of the GPU into a separate device, but it's
>>> unnecessary.
>>
>> What I was trying to say is that we need to map sid0 and sid1 to different
>> context banks.
>>
>> From what I recall, so long as we use the same dt node, the iommu drivert
>> provides no way of doing this.
>>
>> What kgsl does is having a node for the iommu and then subnodes for gfx lpac
>> and secure.
>>
>> The address on the lpac device doesn't really matter. I have very limted
>> knowledge of DTSs but I think we could just leave it out altogether?
> 
> I think, you were poined to the Glymur Iris patches. Another option is
> the QDA driver being submitted too. Both ot them use iommu-map to
> describe the same usecase - a set of SIDs which are used by the device
> but which should not be a part of the defaut set. With it in place you
> don't need to have separate qcom,lpac devices, no additional properties,
> etc. 
> 
> I'd recommend following the same approach.

iiuc, the conclusion in this recent thread is to use child nodes for a
similar case:
https://lore.kernel.org/all/20260618151745.GD231643@ziepe.ca/

-Akhil

> 
>>
>>>
>>>> Add the code to look up that node on initialization.
>>>>
>>>> Signed-off-by: Anna Maniscalco <anna.maniscalco2000@gmail.com>
>>>> ---
>>>>   drivers/gpu/drm/msm/adreno/adreno_gpu.c | 21 ++++++++++++++++++++-
>>>>   drivers/gpu/drm/msm/msm_gpu.h           |  1 +
>>>>   2 files changed, 21 insertions(+), 1 deletion(-)
>>>>
>>
>> Best regards,
>> -- 
>> Anna Maniscalco <anna.maniscalco2000@gmail.com>
>>
>