[PATCH] drm/amd/display: Prevent OTG shutdown during PSR SU

[August Wikerfors]

Hi Leo,

On 2022-09-28 01:13, sunpeng.li at amd.com wrote:
> From: Leo Li <sunpeng.li at amd.com>
> 
> [Why]
> 
> Enabling Z10 optimizations allows DMUB to disable the OTG during PSR
> link-off. This theoretically saves power by putting more of the display
> hardware to sleep. However, we observe that with PSR SU, it causes
> visual artifacts, higher power usage, and potential system hang.
> 
> This is partly due to an odd behavior with the VStartup interrupt used
> to signal DRM vblank events. If the OTG is toggled on/off during a PSR
> link on/off cycle, the vstartup interrupt fires twice in quick
> succession. This generates incorrectly timed vblank events.
> Additionally, it can cause cursor updates to generate visual artifacts.
> 
> Note that this is not observed with PSR1 since PSR is fully disabled
> when there are vblank event requestors. Cursor updates are also
> artifact-free, likely because there are no selectively-updated (SU)
> frames that can generate artifacts.
> 
> [How]
> 
> A potential solution is to disable z10 idle optimizations only when fast
> updates (flips & cursor updates) are committed. A mechanism to do so
> would require some thoughtful design. Let's just disable idle
> optimizations for PSR2 for now.
I can confirm that this patch fixes the issues I had. Thanks!

> Fixes: 7cc191ee7621 ("drm/amd/display: Implement MPO PSR SU")
> Signed-off-by: Leo Li <sunpeng.li at amd.com>
You can add:
Tested-by: August Wikerfors <git at augustwikerfors.se>

Regards,
August Wikerfors