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From: David Brownell <david-b@pacbell.net>
To: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [patch 2.6.26-rc-mm] gpio: max732x driver
Date: Tue, 22 Jul 2008 03:24:38 -0700
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Cc: lkml <linux-kernel@vger.kernel.org>, Eric Miao <eric.y.miao@gmail.com>,
       Jean Delvare <khali@linux-fr.org>, Jack Ren <jack.ren@marvell.com>
References: <200807131918.06377.david-b@pacbell.net> <20080722020542.d180162d.akpm@linux-foundation.org>
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On Tuesday 22 July 2008, Andrew Morton wrote:
> > +?????if ((mask & chip->dir_input) == 0) {
> > +?????????????dev_dbg(&chip->client->dev, "%s port %d is output only\n",
> > +?????????????????????chip->client->name, off);
> > +?????????????return -EACCES;
> 
> I don't think that EACCES is a suitable error code here. ?That's a
> security/permissions sort of thing. ?If userspace is requesting this
> driver to do something which the hardware cannot do then probably
> EINVAL is the appropriate return code.

EINVAL is one of the most ambiguous return codes available.  It's
worth avoiding whenever there's *ANY* more meaningful code!  In this
case, the gpio_direction_input() call is good about returning that
fault code only for bogus GPIO numbers.

EACCES is what you should get trying to open a write-only file for
reading, which seems like a very direct analogy.  That argument is
just fine... it's the particular access request which must be denied,
in this case because hardware itself disallows it rather than a bit
in an inode.

- Dave
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