From mboxrd@z Thu Jan 1 00:00:00 1970 From: okaya@kernel.org (Sinan Kaya) Date: Fri, 3 Aug 2018 13:32:10 -0400 Subject: framebuffer corruption due to overlapping stp instructions on arm64 In-Reply-To: References: <20180803094129.GB17798@arm.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 8/3/2018 1:09 PM, Mikulas Patocka wrote: >>> Most accelerated graphics drivers rely heavily on the ability to map >>> the VRAM normal-non-cacheable (ioremap_wc, basically), and treat it as >>> ordinary memory. >> Yeah, I'd expect framebuffers to be mapped as normal NC. That should be >> fine for prefetchable BARs, no? >> >> Will > So - why does it corrupt data then? I've created this program that > reproduces the data corruption quicky. If I run it on /dev/fb0, I get an > instant failure. Sometimes a few bytes are not written, sometimes a few > bytes are written with a value that should be 16 bytes apart. > > I tried to run it on system RAM mapped with the NC attribute and I didn't > get any corruption - that suggests the the bug may be in the PCIE > subsystem. Note that normal-NC gives you write combining whereas device nGnRE doesn't have any write-combining support. normal-NC is typically mapped to prefetchable BAR space where write-combining is welcome. It could be an issue on the SOC itself too. I suggest you contact your board vendor.