Re: [PATCH 0/7] drm/msm/dpu: simplify VBIF handling

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 3/2/26 1:33 PM, Dmitry Baryshkov wrote:
> On Mon, Mar 02, 2026 at 12:58:42PM +0100, Konrad Dybcio wrote:
>> On 2/27/26 7:36 PM, Dmitry Baryshkov wrote:
>>> Once Konrad asked, what is the use for VBIF_NRT. Answering to his
>>> question revealed that it's not actually used by the DPU driver.
>>>
>>> There are two VBIF interfaces two memory, VBIF_RT and VBIF_NRT with
>>> VBIF_NRT being used only for the offscreen rotator, a separate block
>>> performing writeback operation with the optional 90 degree rotation.
>>> This block will require a separate isntance of the DPU driver, and it is
>>> not supported at this point.
>>
>> (in case someone interested is reading this - patches welcome!)
>>
>>> The only exception to that rule is MSM8996, where VBIF_NRT has also been
>>> used for outputting all writeback data. The DPU driver don't support WB
>>> on that platform and most likely will not in the close feature.
>>
>> Unfortunately, it seems that way. Fortunately, it seems like it's indeed
>> isolated to MSM8996.
>>
>> This patchset is tearing out a lot of abstraction (which would only be
>> useful for that SoC though) - if someone decides to work on it, do you
>> think this should be effectively reverted, or should the NRT VBIF be
>> instantiated in some other, more locallized way?
> 
> I think it should be added as a separate vbif_nrt, added and handled
> without touching the main catalog. The main difference point, xin_id, is
> still in place, it will be easy to add dpu_kms->vbif_nrt as a
> first-class object (instead of forcing the complexity of
> vbif[VBIF_MAX]). In such a case I'd prefer if calling code passes VBIF
> directly to dpu_vbif_set_*() functions instead of passing the index (or
> it might be easier to have a separate wrapper around those functions).
> 
> My opinion is that if something isn't applicable to 99% of cases, those
> 99% should not care about the remaining 1% usecase.

Sure, that makes sense. I wanted to make sure your opinion is put in
writing for the aforementioned "someone comes around to hack on this" case

Konrad