Re: [PATCH v18 0/2] Add memory bandwidth management to NVIDIA Tegra DRM driver

From: Dmitry Osipenko
Date: Sun Jul 18 2021 - 16:59:59 EST

21.06.2021 14:43, Dmitry Osipenko пишет:
> 21.06.2021 14:01, Thierry Reding пишет:
>> On Mon, Jun 21, 2021 at 07:19:15AM +0300, Dmitry Osipenko wrote:
>>> 07.06.2021 01:40, Dmitry Osipenko пишет:
>>>> 01.06.2021 07:21, Dmitry Osipenko пишет:
>>>>> This series adds memory bandwidth management to the NVIDIA Tegra DRM driver,
>>>>> which is done using interconnect framework. It fixes display corruption that
>>>>> happens due to insufficient memory bandwidth.
>>>>> Changelog:
>>>>> v18: - Moved total peak bandwidth from CRTC state to plane state and removed
>>>>> dummy plane bandwidth state initialization from T186+ plane hub. This
>>>>> was suggested by Thierry Reding to v17.
>>>>> - I haven't done anything about the cursor's plane bandwidth which
>>>>> doesn't contribute to overlapping bandwidths for a small sized
>>>>> window because it works okay as-is.
>>>> Thierry, will you take these patches for 5.14?
>>> The display controller does _NOT_WORK_ properly without bandwidth
>>> management.
>> That's surprising. So either it has never worked before (which I think
>> I'd know) or something has caused this regression recently. In the
>> latter case we need to identify what that was and revert (or fix) it.
> The problem is caused by the support of dynamic memory frequency scaling
> which does a good job at keeping memory in a low power state during idle
> time. So display controller may not get enough bandwidth at the start of
> scanout if it won't request BW beforehand. This problem existed for many
> years on T124 and now T20/30 are also affected. The DC of T20 is the
> least tolerant to memory bandwidth troubles.
> This problem is not critical, but it hurts user experience since high
> resolution modes may not work at all and display output may become
> distorted, requiring a DC reset.
>>> Can we get this patch into 5.14? What is the problem?
>> There was not enough time to review and test this, so I didn't feel
>> comfortable picking it up so close to the -rc6 cut-off. I plan to pick
>> this up early in the v5.14 release cycle and target v5.15.
> Thank you for the explanation! It's not uncommon to forget about
> patches, so the silence worries me. I hoped that both the dynamic freq
> scaling and display BW support would be merged around the same time, but
> apparently we got a disconnect here.

Reminder ping :)