(In reply to Sushma from comment #0)
> Created attachment 145408 [details]
> dmesg for FIFO underruns in PIPE B
> 
> The issue is reproducible on Chrome OS WHL device when we connect a 4K
> external monitor to DUT. I was able to reproduce quite often using LG model
> 27UD88-W.
> 
> Attaching the log where I could reproduce the issue even on drm-tip.

Sushma, What is the impact of this issue other than the errors in the log?
What is the reproduction rate?

Can you please attach the dmesg from drmtip, that will be helpful to investigate.

Update for myself: On our CI system last seen FIFO underrun on WHL is drmtip_334 (1 month, 3 weeks old).

Lakshmi, the dmesg log that I have attached is from drmtip. WHL is on 4.19 kernel. I am seeing sporadic flickers when the fifo underruns occur. It is very frequent when I use USB-C to USB-C cable to connect external monitor - once in three tries. Especially, while using the LG monitor on which I am reporting the issue.

Lakshmi was asking using latest drm-tip that is today on Linux version 5.3.0. He was asking to try with that I think.

Created attachment 145429 [details]
dmesg for FIFO underruns in PIPE B

Even though I was seeing flickers during mode setup, it was comparatively difficult to reproduce the fifo underrun with latest drmtip. I used two 4K monitors here, LG monitor was connected via USB-C cable and Dell monitor was connected via HDMI cable.

(In reply to Sushma from comment #4)
> Created attachment 145429 [details]
> dmesg for FIFO underruns in PIPE B
> 
> Even though I was seeing flickers during mode setup, it was comparatively
> difficult to reproduce the fifo underrun with latest drmtip. I used two 4K
> monitors here, LG monitor was connected via USB-C cable and Dell monitor was
> connected via HDMI cable.

Thanks for the feedback.

The flickers issue was first introduced in driver with OS build version 12370 when the code added to support Render Compression in i915 driver.  The code has been reversed starting OS build 12449 due to multiple issues reported with the original patch.
 
Therefore, this should be no longer an issue since 12449 build.  I have verified both bad (buid 12443) and good (build 12450) OS images.  I verified with 2 external 4K panels Dell and Samsung.  For FIFO watermark related issues, panel models should not make a difference as long the same resolution and refresh rates are consistent.

(In reply to Jason Le from comment #6)
> The flickers issue was first introduced in driver with OS build version
> 12370 when the code added to support Render Compression in i915 driver.  The
> code has been reversed starting OS build 12449 due to multiple issues
> reported with the original patch.
>  
> Therefore, this should be no longer an issue since 12449 build.  I have
> verified both bad (buid 12443) and good (build 12450) OS images.  I verified
> with 2 external 4K panels Dell and Samsung.  For FIFO watermark related
> issues, panel models should not make a difference as long the same
> resolution and refresh rates are consistent.

@Jason, Thanks for the feedback.

@Sushma, based on the above feedback can we close this issue?

I was able to reproduce the issue on 12480 and the above release images where I did confirm that render frame buffer patches were reverted. I have posted the logs for the same.

-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been closed from further activity.

You can subscribe and participate further through the new bug through this link to our GitLab instance: https://gitlab.freedesktop.org/drm/intel/issues/429.