Messages in this thread | | | From | Ramana Radhakrishnan <> | Date | Mon, 6 Aug 2018 09:04:33 +0100 | Subject | Re: framebuffer corruption due to overlapping stp instructions on arm64 |
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On Sun, Aug 5, 2018 at 10:36 PM, Pavel Machek <pavel@ucw.cz> 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.
Ramana
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