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

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Date:   Thu, 29 Sep 2016 00:22:25 +0200
From:   Noralf Trønnes <noralf@...nnes.org>
To:     Eric Anholt <eric@...olt.net>, 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
Subject: Re: [PATCH v3 2/7] i2c: bcm2835: Protect against unexpected TXW/RXR
 interrupts


Den 29.09.2016 00:00, skrev Eric Anholt:
> 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.

Maybe you're able to explain the issues I had with reset:
https://github.com/raspberrypi/linux/issues/1653

Should we put your note into the commit message?
It will most likely be lost if it just stays in this email.

Noralf.