linux-kernel - Re: [PATCH] leds-pca955x: Fix race condition while setting brightness on several LEDs

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Message-Id: <20120510144016.3a1b006c.akpm@linux-foundation.org>
Date:	Thu, 10 May 2012 14:40:16 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alexander Stein <alexander.stein@...tec-electronic.com>
Cc:	Richard Purdie <rpurdie@...ys.net>, linux-kernel@...r.kernel.org,
	Bryan Wu <bryan.wu@...onical.com>
Subject: Re: [PATCH] leds-pca955x: Fix race condition while setting
 brightness on several LEDs

On Wed,  8 Feb 2012 13:44:08 +0100
Alexander Stein <alexander.stein@...tec-electronic.com> wrote:

> When issuing the following command:
> for I in 0 1 2 3 4 5 6 7; do
>   echo 0 > /sys/class/leds/pca955x\:${I}/brightness;
> done
> It is possible that all the pca955x_read_ls calls are done sequentially
> before any pca955x_write_ls call is done. This updates the LS only to the
> last LED update in its set.
> Fix this by using a global lock for the pca995x device during
> pca955x_led_work.

There's the bugfix.

> Also used a struct for shared data bewteen all LEDs.

And there's an apparently unrelated change whcih created a *lot* of
noise in the patch.  It would be good to separate these things, with
the bugfix being the first change.

> ...
>
> -static inline u8 pca955x_ledsel(u8 oldval, int led_num, int state)
> +static inline u8 pca955x_ledel(u8 oldval, int led_num, int state)

Why was this function renamed, and what does "ledel" mean?

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