Re: [PATCH V5 6/7] i2c: tegra: fix PIO rx/tx residual transfer check

[Bitan Biswas]

On 6/13/19 5:28 AM, Dmitry Osipenko wrote:
> 13.06.2019 14:30, Bitan Biswas ÐÐÑÐÑ:
> > On 6/12/19 7:30 AM, Dmitry Osipenko wrote:
> > > 11.06.2019 13:51, Bitan Biswas ÐÐÑÐÑ:
> > > > Fix expression for residual bytes(less than word) transfer
> > > > in I2C PIO mode RX/TX.
> > > >
> > > > Signed-off-by: Bitan Biswas <bbiswas@xxxxxxxxxx>
> > > > ---
> > >
> > > [snip]
> > >
> > > >  ÂÂÂÂÂÂÂÂÂ /*
> > > > - * Update state before writing to FIFO. If this casues us
> > > > + * Update state before writing to FIFO. If this causes us
> > > >  ÂÂÂÂÂÂÂÂÂÂ * to finish writing all bytes (AKA buf_remaining goes to
> > > > 0) we
> > > >  ÂÂÂÂÂÂÂÂÂÂ * have a potential for an interrupt (PACKET_XFER_COMPLETE is
> > > > - * not maskable). We need to make sure that the isr sees
> > > > -ÂÂÂÂÂÂÂÂ * buf_remaining as 0 and doesn't call us back re-entrantly.
> > > > +ÂÂÂÂÂÂÂÂ * not maskable).
> > > >  ÂÂÂÂÂÂÂÂÂÂ */
> > > >  ÂÂÂÂÂÂÂÂÂ buf_remaining -= words_to_transfer * BYTES_PER_FIFO_WORD;
> > >
> > > Looks like the comment could be removed altogether because it doesn't
> > > make sense since interrupt handler is under xfer_lock which is kept
> > > locked during of tegra_i2c_xfer_msg().
> > I would push a separate patch to remove this comment because of
> > xfer_lock in ISR now.
> >
> > > Moreover the comment says that "PACKET_XFER_COMPLETE is not maskable",
> > > but then what I2C_INT_PACKET_XFER_COMPLETE masking does?
> > I2C_INT_PACKET_XFER_COMPLETE masking support available in Tegra chips
> > newer than Tegra30 allows one to not see interrupt after Packet transfer
> > complete. With the xfer_lock in ISR the scenario discussed in comment
> > can be ignored.
>
> Also note that xfer_lock could be removed and replaced with a just
> irq_enable/disable() calls in tegra_i2c_xfer_msg() because we only care
> about IRQ not firing during of the preparation process.
This should need sufficient testing hence let us do it in a different 
series.

> It also looks like tegra_i2c_[un]nmask_irq isn't really needed and all
> IRQ's could be simply unmasked during the driver's probe, in that case
> it may worth to add a kind of "in-progress" flag to catch erroneous
> interrupts.
TX interrupt needs special handling if this change is done. Hence I 
think it should be taken up after sufficient testing in a separate patch.

-regards,
 Bitan