Re: [PATCH 4/6] arm64/io: Provide a WC friendly __iowriteXX_copy()

Catalin Marinas
2024-02-27T10:37:28Z

On Tue, Feb 20, 2024 at 09:17:08PM -0400, Jason Gunthorpe wrote:
> +/*
> + * This generates a memcpy that works on a from/to address which is aligned to
> + * bits. Count is in terms of the number of bits sized quantities to copy. It
> + * optimizes to use the STR groupings when possible so that it is WC friendly.
> + */
> +#define memcpy_toio_aligned(to, from, count, bits) \
> + ({ \
> + volatile u##bits __iomem *_to = to; \
> + const u##bits *_from = from; \
> + size_t _count = count; \
> + const u##bits *_end_from = _from + ALIGN_DOWN(_count, 8); \
> + \
> + for (; _from < _end_from; _from += 8, _to += 8) \
> + __const_memcpy_toio_aligned##bits(_to, _from, 8); \
> + if ((_count % 8) >= 4) { \
> + __const_memcpy_toio_aligned##bits(_to, _from, 4); \
> + _from += 4; \
> + _to += 4; \
> + } \
> + if ((_count % 4) >= 2) { \
> + __const_memcpy_toio_aligned##bits(_to, _from, 2); \
> + _from += 2; \
> + _to += 2; \
> + } \
> + if (_count % 2) \
> + __const_memcpy_toio_aligned##bits(_to, _from, 1); \
> + })

Do we actually need all this if count is not constant? If it's not
performance critical anywhere, I'd rather copy the generic
implementation, it's easier to read.

Otherwise, apart from the __raw_writeq() typo that Will mentioned, the
patch looks fine to me.

--
Catalin