Re: Questions about i2c_transfer() usage in timer context...

[Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>]

Bonjour Stéphane,

On Mon, 20 Feb 2012 14:01:52 +0100, Stephane Grosjean wrote:
> I'm facing a deadlock regarding a timer callback which is only calling 
> i2c_transfer(), and I wonder if this comes from that call: I first 
> googled and found that i2c_transfer() may sleep (which is forbidden in 
> my timer callback) but when I have a look the beginning of the function, 
> it starts to check if it is in any atomic context, before trying to 
> acquire  a lock...
> 
> So I'm afraid I'm lost and I hope someone will be able to understand to 
> that question: might i2c_transfer() be used in a timer callback or 
> should I handle my periodic call to i2c_tranfer() by means of a delayed 
> work?

Depends on the underlying I2C adapter driver. One of the sleep causes
is indeed the acquisition of the mutex in i2c_transfer(). However the
function then calls a driver specific callback function
(adap->algo->master_xfer) which may or may not sleep too depending on
the implementation. So if you want your code to be portable, you have to
assume that it may sleep, which means you indeed have to use a delayed
work.

HTH,
-- 
Jean Delvare