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) > + len = i2c_dw_recv_len(dev, tmp); > + else > + i2c_dw_abort(dev); -- With Best Regards, Andy Shevchenko
