linux-kernel - Re: [PATCH v3 2/7] i2c: bcm2835: Protect against unexpected TXW/RXR interrupts

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Message-ID: <87oa37fzx6.fsf@eliezer.anholt.net>
Date:   Wed, 28 Sep 2016 15:00:05 -0700
From:   Eric Anholt <eric@...olt.net>
To:     Noralf Trønnes <noralf@...nnes.org>,
        wsa@...-dreams.de, swarren@...dotorg.org
Cc:     linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rpi-kernel@...ts.infradead.org,
        Noralf Trønnes <noralf@...nnes.org>
Subject: Re: [PATCH v3 2/7] i2c: bcm2835: Protect against unexpected TXW/RXR interrupts

Noralf Trønnes <noralf@...nnes.org> writes:

> If an unexpected TXW or RXR interrupt occurs (msg_buf_remaining == 0),
> the driver has no way to fill/drain the FIFO to stop the interrupts.
> In this case the controller has to be disabled and the transfer
> completed to avoid hang.
>
> (CLKT | ERR) and DONE interrupts are completed in their own paths, and
> the controller is disabled in the transfer function after completion.
> Unite the code paths and do disabling inside the interrupt routine.
>
> Clear interrupt status bits in the united completion path instead of
> trying to do it on every interrupt which isn't necessary.
> Only CLKT, ERR and DONE can be cleared that way.
>
> Add the status value to the error value in case of TXW/RXR errors to
> distinguish them from the other S_LEN error.

I was surprised that not writing the TXW/RXR bits on handling their
interrupts was OK, given that we were doing so before, but it's a level
interrupt and those bits are basically ignored on write.

This patch and 3, 4, and 6 are:

Reviewed-by: Eric Anholt <eric@...olt.net>

Patch 5 is:

Acked-by: Eric Anholt <eric@...olt.net>

Note for future debug: The I2C_C_CLEAR on errors will take some time to
resolve -- if you were in non-idle state and I2C_C_READ, it sets an
abort_rx flag and runs through the state machine to send a NACK and a
STOP, I think.  Since we're setting CLEAR without I2CEN, that NACK will
be hanging around queued up for next time we start the engine.

Patch 7 I had questions about but probably will send an ack when you
reply.

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