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

[Bitan Biswas]

On 6/14/19 6:02 AM, Dmitry Osipenko wrote:
> 14.06.2019 12:50, Bitan Biswas ÐÐÑÐÑ:
> > 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]
> > > > >
> > > > > >  ÂÂÂÂÂÂÂÂÂÂ /*
> > > > > > - * Update state before writing to FIFO. If this casues us
> > > > > > + * Update state before writing to FIFO. If this causes us
> > > > > >  ÂÂÂÂÂÂÂÂÂÂÂ * to finish writing all bytes (AKA buf_remaining goes to
> > > > > > 0) we
> > > > > >  ÂÂÂÂÂÂÂÂÂÂÂ * 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).
> > > > > >  ÂÂÂÂÂÂÂÂÂÂÂ */
> > > > > >  ÂÂÂÂÂÂÂÂÂÂ 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.
>
> I don't think that there is much to test here since obviously it should work.
I shall push a patch for this as basic i2c read write test passed.

> > > 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.
>
> This one is indeed a bit more trickier. Probably another alternative could be to keep GIC
> interrupt disabled while no transfer is performed, then you'll have to request interrupt
> in a disabled state using IRQ_NOAUTOEN flag.
>
> And yes, that all should be a separate changes if you're going to implement them.
OK

-Thanks,
 Bitan