Re: [PATCH 2/2] PCI/sysfs: Fix read byte order in pci_read_legacy_io()

[sashiko-bot@kernel.org]

> pci_read_legacy_io() passes the sysfs buffer directly to pci_legacy_read():
> 
>   return pci_legacy_read(bus, off, (u32 *)buf, count);
> 
> The PowerPC implementation stores the result as a native-endian integer:
> 
>   *((u16 *)val) = in_le16(addr);
> 
> On big-endian PowerPC this stores the bytes in the wrong order, so
> a 2-byte read of a device register returns different bytes than two
> 1-byte reads at the same addresses.  The same applies to 4-byte
> reads.  On little-endian the native byte order already matches PCI
> I/O port byte order, so the conversion is a no-op.
> 
> Thus, let pci_legacy_read() store into a local u32 variable, then
> copy the I/O port value to the sysfs buffer using put_unaligned_le16()
> and put_unaligned_le32() for the 2 and 4 byte cases, converting from
> the native integer to little-endian byte order matching PCI I/O port
> space.
> 
> No changes are needed for the Alpha platform.
> 
> The legacy_io file is root-only and exists only on Alpha and PowerPC,
> the two architectures that define HAVE_PCI_LEGACY.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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