Re: [PATCH] sparc: Remove IO memcpy and memset from sparc code

[Arnd Bergmann]

On Thu, Oct 29, 2026, at 15:53, Julian Vetter wrote:
> Remove the IO memcpy and memset from sparc specific code and fall back
> to the implementations from lib/iomem_copy.c. They use word accesses if
> the buffers are aligned and only fall back to byte accesses for
> potentially unaligned parts of a buffer, while the sparc versions always
> use byte-wise readb()/writeb() accesses. Other architectures, such as
> arm64, csky, loongarch and parisc, have already been converted to the
> generic implementation.
>
> This does not drop any memory barriers. The sparc versions don't use
> mb(), and the rmb()/wmb() implied by readb()/writeb() on sparc32 and
> sparc64 are only compiler barriers.

Hi Julian,

I suspect the sparc64 patch is wrong because the generic
code relies on __raw_readq()/__raw_readl() to produce
native-endian data, while the sparc64 version looks like
they work on little-endian data the same way as readq()/readl().

Do you know if the PCI host bridge on sparc64 does an implicit
byte swap for memory space? If it does, the __raw_ accessors
have to flip swap the data another time for this to work.

      Arnd