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

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Message-ID: <20140309202107.GA2835@katana>
Date:	Sun, 9 Mar 2014 21:21:07 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Mike Looijmans <mike.looijmans@...ic.nl>
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 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.


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