Re: [PATCH] drm/i915/display/lspcon: Increase LSPCON mode settle timeout

From: Pablo Ceballos
Date: Thu Oct 06 2022 - 18:59:45 EST

On Tue, Oct 4, 2022 at 10:38 AM Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx> wrote:
> Got any bug report with more info, or any other details to back this up?
> This is kind of thin. What's the 800 ms based on?

This issue affected several different CometLake-based Chrome OS device
designs. The details of the original report are in the Google partner
issue tracker (issue # 178169843), but I believe this requires a
Google partner account to access:

The summary is that we were seeing these "*ERROR* LSPCON mode hasn't
settled" messages in the kernel logs followed by the display not
working at all. We increased the timeout to 500ms while investigation
continued and this reduced the number of occurrences of this issue:

The problem continued to occur on about 2% of devices even after
increasing the timeout to 500ms. The investigation continued in issue
# 188035814, with engineers from Parade and Intel involved.
Ultimately, the recommendation from Intel engineers was to increase
the timeout further:

The timeout was then increased to 1000ms:

I recently ran 100 reboot trials on one device and found that the
median time for the LSPCON mode to settle was 440ms and the max was
444ms. But we know from the original reports that even after we set
the timeout to 500ms the issue continued to happen on some small
percentage of devices. So this is why I picked the larger value of