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

From: Dmitry Osipenko
Date: Thu Jun 13 2019 - 11:28:13 EST

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]
>>> - * 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).
>>> 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.

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