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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <0c943ee9-d152-79c4-2ad7-8a88c2d9c960@tronnes.org>
Date:   Sun, 2 Oct 2016 16:19:57 +0200
From:   Noralf Trønnes <noralf@...nnes.org>
To:     Stefan Wahren <stefan.wahren@...e.com>,
        Eric Anholt <eric@...olt.net>, wsa@...-dreams.de,
        swarren@...dotorg.org
Cc:     linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 2/7] i2c: bcm2835: Protect against unexpected TXW/RXR
 interrupts


Den 29.09.2016 07:37, skrev Stefan Wahren:
>> Noralf Trønnes <noralf@...nnes.org> hat am 29. September 2016 um 00:22
>> geschrieben:
>>
>>
>>
>> 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.
> I prefer to have this kind of information as a code comment.

Eric, does this look good to you as a code comment:

/*
  * Note about I2C_C_CLEAR on error:
  * 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. Since we're setting CLEAR
  * without I2CEN, that NACK will be hanging around queued up for next time
  * we start the engine.
  */


If it is, I'll resend the series with this change and add all the ack's 
and r-b's.

Noralf.