Re: [PATCH 2/2] i2c: designware: abort the transfer if receiving byte count of 0

[Yann Sionneau]

Hi,

Le 11/08/2023 à 16:01, Andy Shevchenko a écrit :
> On Fri, Aug 11, 2023 at 02:46:24PM +0200, Yann Sionneau wrote:
> > From: Yann Sionneau <ysionneau@xxxxxxxxx>
> >
> > Context:
> > It's not clear whether Linux SMBus stack supports receiving 0
> > as byte count for SMBus read data block.
> >
> > Linux supports SMBus v2.0 spec, which says "The byte count may not be 0."
> > Which does not seem very clear to me, as a non-native speaker.
> > (Note that v3.0 of the spec says "The byte count may be 0.")
> >
> > Some drivers explicitly return -EPROTO in case of byte count 0.
> >
> > The issue:
> > Regardless of whether Linux supports byte count of 0, if this happens
> > the i2c-designware driver goes into an unrecoverable state holding
> > SCL low if the IP is synthesized with the IC_EMPTYFIFO_HOLD_MASTER_EN
> > parameter.
> >
> > The fix proposed by this patch:
> > Abort the transfer by sending a STOP condition on the bus.
> >
> > Another approach would be to ignore the issue and let the driver
> > timeout and disable the IP. The IP disabling is fixed by the previous
> > patch in this patch series.
> > The current patch just makes the recovery faster since Abort is sent
> > directly without waiting for the timeout to happen. With this patch,
> > disabling the IP is not necessary anymore.
> ...
>
> > +				if ((tmp <= I2C_SMBUS_BLOCK_MAX) && (tmp != 0))
> 				if (tmp && tmp <= I2C_SMBUS_BLOCK_MAX)

I find the tmp != 0 "more obvious", I am more used to "just tmp" when 
it's a pointer or a boolean, but maybe it's just me!

I'll fix that in the V2 :)

> > +					len = i2c_dw_recv_len(dev, tmp);
> > +				else
> > +					i2c_dw_abort(dev);
Thanks!