On Mon 2018-08-06 09:04:33, Ramana Radhakrishnan wrote: > On Sun, Aug 5, 2018 at 10:36 PM, Pavel Machek wrote: > > Hi! > > > >> > I tried to use a PCIe graphics card on the MacchiatoBIN board and I hit a > >> > strange problem. > >> > > >> > When I use the links browser in graphics mode on the framebuffer, I get > >> > occasional pixel corruption. Links does memcpy, memset and 4-byte writes > >> > on the framebuffer - nothing else. > >> > > >> > I found out that the pixel corruption is caused by overlapping unaligned > >> > stp instructions inside memcpy. In order to avoid branching, the arm64 > >> > memcpy implementation may write the same destination twice with different > >> > alignment. If I put "dmb sy" between the overlapping stp instructions, the > >> > pixel corruption goes away. > >> > > >> > This seems like a hardware bug. Is it a known errata? Do you have any > >> > workarounds for it? > >> > >> Yes fix Links not to use memcpy on the framebuffer. > >> It is undefined behavior to use device memory with memcpy. > > > > No, I don't think so. Why do you think so? > > It is undefined behaviour in the architecture. Why do you think so? Pointer to documentation would be helpful. Normal access is used for mmapped areas, and I don't think we want to change that. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html