Messages in this thread |  | | Subject | Re: [PATCH] gpu/drm: Remove TTM_PL_FLAG_WC of VRAM to fix writecombine issue for Loongson64 | From | Christian König <> | Date | Sun, 9 Aug 2020 14:13:15 +0200 |
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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.
Regards, Christian.
> > Thanks. > > - Jiaxun
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