linux-kernel - Re: [PATCH 03/14 v3] Input: atmel_mxt_ts - refactor mxt_read/write

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Date:	Wed, 9 May 2012 00:25:18 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	Daniel Kurtz <djkurtz@...omium.org>,
	Henrik Rydberg <rydberg@...omail.se>,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	Nick Dyer <nick.dyer@...ev.co.uk>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, Benson Leung <bleung@...omium.org>,
	Yufeng Shen <miletus@...omium.org>
Subject: Re: [PATCH 03/14 v3] Input: atmel_mxt_ts - refactor
 mxt_read/write_reg to take a length

On Wed, May 09, 2012 at 09:05:00AM +0200, Jean Delvare wrote:
> Hi Dmirty,
> 
> On Tue, 8 May 2012 22:54:11 -0700, Dmitry Torokhov wrote:
> > Hi Daniel,
> > 
> > On Wed, Apr 18, 2012 at 09:21:48PM +0800, Daniel Kurtz wrote:
> > > +	ret = i2c_transfer(client->adapter, xfer, 2);
> > > +	if (ret != 2) {
> > > +		dev_err(&client->dev, "i2c read reg failed (%d)\n", ret);
> > > +		if (ret >= 0)
> > > +			ret = -EIO;
> > >  	}
> > >  
> > > -	return 0;
> > > +	return (ret == 2) ? 0 : ret;
> > >  }
> > 
> > Would prefer:
> > 
> > 	ret = i2c_transfer(client->adapter, xfer, ARRAY_SIZE(xfer));
> > 	if (ret != ARRAY_SIZE(xfer)) {
> > 		if (ret >= 0)
> > 			ret = -EIO;
> > 		dev_err(&client->dev, "i2c read reg failed (%d)\n", ret);
> > 		return ret;
> > 	}
> > 
> > 	return 0;
> > 
> > 
> > Or maybe we need i2c_transfer_exact() wrapper? Jean?
> 
> What would this function do? Return 0 on success instead of the number
> of transferred messages? And -EIO on partial transfers?

Yes, exactly.

> 
> That would make sense. Partial success is a rare case anyway, and
> recovery possibilities are even rarer. I think most drivers don't
> bother and either retry the whole transaction or fail right away. In
> fact the number of messages successfully transferred is more useful to
> diagnose problems during driver development or debugging.
> 
> Feel free to write and send a patch introducing i2c_transfer_exact().
> It would make sense to have it log a debug message on partial success,
> as it is a rare case. Bonus points if you also sent one or more patches
> converting (some of) the existing callers to make use of the new
> function.

OK, thanks.

-- 
Dmitry
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