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

[Anna Maniscalco]

On 10/22/26 2:54 PM, Anna Maniscalco wrote:
> On 7/9/26 9:39 PM, Dmitry Baryshkov wrote:
>> On Thu, Jul 09, 2026 at 05:54:23PM +0300, Dmitry Baryshkov wrote:
>>> On Thu, Jul 09, 2026 at 07:12:39PM +0530, Akhil P Oommen wrote:
>>>> 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/
>>> Let me check internally.
>> After a brief discussion: it can be either, depending on what suites
>> better (and if you can persuade DMA / IOMMU maintainers to let one extra
>> bus or not).
>>
> One thing sashiko is pointing out is that new dt should work with hold 
> kernel so, in general moving sid1 from there would break it since old 
> kernels don't know how to handle them separately.
>
> Not sure how to address this.
>
> Best regards,

Also, looking into iommu-map, it seems like I would ultimately still 
need to add a child device.

Best regards,
-- 
Anna Maniscalco <anna.maniscalco2000 at gmail.com>