Re: [PATCH v2 1/3] net: sfp: add workaround for Realtek RTL8672 and RTL9601C chips

Pali Rohár
2021-01-07T19:19:39Z

On Thursday 07 January 2021 17:40:06 Russell King - ARM Linux admin wrote:
> On Thu, Jan 07, 2021 at 06:19:23PM +0100, Andrew Lunn wrote:
> > Did we loose the comment:
> >
> > /* Some modules (Nokia 3FE46541AA) lock up if byte 0x51 is read as a
> > * single read. Switch back to reading 16 byte blocks ...
> >
> > That explains why 16 is used. Given how broken stuff is and the number
> > of workaround we need, we should try to document as much as we cam, so
> > we don't break stuff when adding more workarounds.
>
> It is _not_ why 16 is used at all.
>
> We used to read the whole lot in one go. However, some modules could
> not cope with a full read - also some Linux I2C drivers struggled with
> it.
>
> So, we reduced it down to 16 bytes. See commit 28e74a7cfd64 ("net: sfp:
> read eeprom in maximum 16 byte increments"). That had nothing to do
> with the 3FE46541AA, which came along later. It has been discovered
> that 3FE46541AA reacts badly to a single byte read to address 0x51 -
> it locks the I2C bus. Hence why we can't just go to single byte reads
> for every module.
>
> So, the comment needs to be kept to explain why we are unable to go
> to single byte reads for all modules. The choice of 16 remains
> relatively arbitary.

Do you have an idea where to put a comment?