i3c: fix big-endian FIFO transfers

Short MMIO transfers that are not a multiple of four bytes in size need
a special case for the final bytes, however the existing implementation
is not endian-safe and introduces an incorrect byteswap on big-endian
kernels.

This usually does not cause problems because most systems are
little-endian and most transfers are multiple of four bytes long, but
still needs to be fixed to avoid the extra byteswap.

Change the special case for both i3c_writel_fifo() and i3c_readl_fifo()
to use non-byteswapping writesl() and readsl() with a single element
instead of the byteswapping writel()/readl() that are meant for individual
MMIO registers. As data is copied between a FIFO and a memory buffer,
the writesl()/readsl() loops are typically based on __raw_readl()/
__raw_writel(), resulting in the order of bytes in the FIFO to match
the order in the buffer, regardless of the CPU endianess.

The earlier versions in the dw-i3c and i3c-master-cdns had a correct
implementation, but the generic version that was recently added broke it.

Fixes: 733b4393 ("i3c: master: Add inline i3c_readl_fifo() and i3c_writel_fifo()")
Cc: Manikanta Guntupalli <manikanta.guntupalli@amd.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Jorge Marques <jorge.marques@analog.com>
Link: https://lore.kernel.org/r/20250924201837.3691486-1-arnd@kernel.org


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>