On 08/09/2020 08:13 PM, Christian König wrote:
Am 08.08.20 um 15:50 schrieb Jiaxun Yang:
在 2020/8/8 下午9:41, Thomas Bogendoerfer 写道:
On Sat, Aug 08, 2020 at 03:25:02PM +0800, Tiezhu Yang wrote:
Loongson processors have a writecombine issue that maybe failed to
write back framebuffer used with ATI Radeon or AMD GPU at times,
after commit 8a08e50cee66 ("drm: Permit video-buffers writecombine
mapping for MIPS"), there exists some errors such as blurred screen
and lockup, and so on.
Remove the flag TTM_PL_FLAG_WC of VRAM to fix writecombine issue for
Loongson64 to work well with ATI Radeon or AMD GPU, and it has no any
influence on the other platforms.
well it's not my call to take or reject this patch, but I already
indicated it might be better to disable writecombine on the CPU
detection side (or do you have other devices where writecombining
works ?). Something like below will disbale it for all loongson64 CPUs.
If you now find out where it works and where it doesn't, you can even
reduce it to the required minium of affected CPUs.
Hi Tiezhu, Thomas,
Yes, writecombine works well on LS7A's internal GPU....
And even works well with some AMD GPUs (in my case, RX550).
In this case the patch is a clear NAK since you haven't root caused
the issue and are just working around it in a very questionable manner.
Tiezhu, is it possible to investigate the issue deeper in Loongson?
Probably we just need to add some barrier to maintain the data
coherency,
or disable writecombine for AMD GPU's command buffer and leave
texture/frame
buffer wc accelerated.
Have you moved any buffer to VRAM and forgot to add an HDP
flush/invalidate?
The acceleration is not much of a problem, but if WC doesn't work in
general you need to disable it for the whole CPU and not for
individual drivers.
Hi Thomas, Jiaxun and Christian,
Thank you very much for your suggestions.
Actually, this patch is a temporary solution to just make it work well,
it is not a proper and final solution.
I understand your opinions, it will take some time to find the root cause.
Thanks,
Tiezhu
Regards,
Christian.
Thanks.
- Jiaxun
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