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Date: Mon, 10 Aug 2020 08:58:13 +0800 From: Tiezhu Yang <yangtiezhu@...ngson.cn> To: Christian König <christian.koenig@....com>, Jiaxun Yang <jiaxun.yang@...goat.com>, Thomas Bogendoerfer <tsbogend@...ha.franken.de> Cc: Alex Deucher <alexander.deucher@....com>, Huacai Chen <chenhc@...ote.com>, linux-mips@...r.kernel.org, amd-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] gpu/drm: Remove TTM_PL_FLAG_WC of VRAM to fix writecombine issue for Loongson64 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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