Re: [PATCH net-next v5] net: sfp: extend SMBus support

[Andrew Lunn]

On Fri, Jan 16, 2026 at 02:43:47PM +0100, Jonas Jelonek wrote:
> Hi,
> 
> On 16.01.26 14:23, Maxime Chevallier wrote:
> > I think Russell pointed it out, but I was also wondering the same.
> > How do we deal with controllers that cannot do neither block nor
> > single-byte, i.e. that can only do word access ?
> >
> > We can't do transfers that have an odd length. And there are some,
> > see sfp_cotsworks_fixup_check() for example.
> >
> > Maybe these smbus controller don't even exist, but I think we should
> > anyway have some log saying that this doesn't work, either at SFP
> > access time, or at init time.
> 
> I tried to guard that in the sfp_i2c_configure() right now. The whole path
> to allow SMBus transfers is only allowed if there's at least byte access. For
> exactly the reason that we need byte access in case of odd lengths.

Is there a use case for odd lengths? Apart from 1.

> This of course rules out any controllers which just can do word access.

There are some PHYs embedded within SFPs which kill the bus if you do
anything but 1 byte access. There is a quirk for it. We should refuse
to drive the SFP if we have such an SFP and an I2C bus that can only
do words.

	Andrew