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

[Bitan Biswas]

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]
>
> >   		/*
> > -		 * Update state before writing to FIFO.  If this casues us
> > +		 * Update state before writing to FIFO.  If this causes us
> >   		 * to finish writing all bytes (AKA buf_remaining goes to 0) we
> >   		 * have a potential for an interrupt (PACKET_XFER_COMPLETE is
> > -		 * not maskable).  We need to make sure that the isr sees
> > -		 * buf_remaining as 0 and doesn't call us back re-entrantly.
> > +		 * not maskable).
> >   		 */
> >   		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.

-regards,
 Bitan