linux-kernel - Re: gpios search behaviour for gpio from

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Message-ID: <20150924084324.GK1536@lahna.fi.intel.com>
Date:	Thu, 24 Sep 2015 11:43:24 +0300
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Olliver Schinagl <oliver+list@...inagl.nl>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Grant Likely <grant.likely@...aro.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Alexandre Courbot <gnurou@...il.com>,
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: gpios search behaviour for gpio from _DSD

On Thu, Sep 24, 2015 at 09:25:06AM +0200, Olliver Schinagl wrote:
> Hey list, Mika,
> 
> With commit 0d9a693cc86 the following snippet of code was added:
> 
> +       /* Try first from _DSD */
> +       for (i = 0; i < ARRAY_SIZE(suffixes); i++) {
> +               if (con_id && strcmp(con_id, "gpios")) {
> +                       snprintf(propname, sizeof(propname), "%s-%s",
> +                                con_id, suffixes[i]);
> 
> and I was wondering why the gpios suffix is singled out. Are we not allowed
> to check for all the strings in the suffixes array? Is gpios special or is
> gpio simply not allowed. If that strcmp check would be removed, would bad
> things happen?

We default to "gpios". So if you pass "reset" we actually look for
proprerty "reset-gpios". This is the recommend syntax AFAIK.

> Also, just to educate myself, isn't relying on left to right parsing
> complier specifc? E.g. if con_id is null, we end up passing NULL to strcmp
> and atleast for libc can cause segfaults iirc.

'&&' is so called short circuit operator so if we already know that
con_id is NULL we never evaluate the remaining conditions.
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