linux-kernel - Re: [PATCH] i2c-davinci: Handle signals gracefully

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Message-ID: <531D92F7.7080509@topic.nl>
Date:	Mon, 10 Mar 2014 11:24:55 +0100
From:	Mike Looijmans <mike.looijmans@...ic.nl>
To:	Wolfram Sang <wsa@...-dreams.de>
CC:	<linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<nsekhar@...com>, <khilman@...prootsystems.com>,
	<davinci-linux-open-source@...ux.davincidsp.com>
Subject: Re: [PATCH] i2c-davinci: Handle signals gracefully

On 03/09/2014 09:21 PM, Wolfram Sang wrote:
> On Thu, Jan 09, 2014 at 12:11:25PM +0100, Mike Looijmans wrote:
>> When a signal is caught while the i2c-davinci bus driver is transferring,
>> the drive just "abandons" the transfer and leaves the controller to fend
>> for itself. The next I2C transaction will find the controller in an
>> undefined state and often results in a stream of "initiating i2c bus recovery"
>> messages until the controller arrives in a defined state. This behaviour
>> also sends out "half" or possibly even mixed messages to I2C client
>> devices which may put them in an undesired state as well.
>>
>> This patch fixes this issue by always attempting to finish the current
>> transaction, and then check on a pending signal. It either reports
>> success if all data has been transferred, or it returns failure when
>> the transaction was aborted. This keeps the controller in a defined
>> state, and is also much friendlier towards client devices, because
>> it will only send complete messages.
>
> Even more, you should complete the whole transfer. There are devices
> where things can really go wrong if you send a half-complete command and
> then start with the next one. So, not checking signals at all is the way
> to go for I2C drivers. There is some cruft left, so I am happy about
> patches fixing that, with testing on real HW. Like yours here.

I agree.

I know the Zynq (using a cadence controller) also lets signals interrupt I2C 
transfers, so I'll propose a patch to Xilinx and CC to you and linux-i2c to 
completely remove signal handling from that driver as well.

Mike


Met vriendelijke groet / kind regards,

Mike Looijmans

TOPIC Embedded Systems
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