linux-kernel - Re: [PATCH] Rationalise ACPI backlight implementation

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Message-Id: <20080127211013.1ddaa6a1.akpm@linux-foundation.org>
Date:	Sun, 27 Jan 2008 21:10:13 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	Len Brown <lenb@...nel.org>, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH] Rationalise ACPI backlight implementation

On Mon, 28 Jan 2008 01:25:50 +0000 Matthew Garrett <mjg59@...f.ucam.org> wrote:

> On Sat, Jan 26, 2008 at 10:00:45PM -0800, Andrew Morton wrote:
> > - Create a new /sys node with a new name which has the new semantics.
> 
> The semantics are the same as they always have been - values between 0 
> and max_brightness are valid values. If you've made assumptions about 
> what max_brightness is, then that's a bug in the userspace application 
> rather than a change in the semantics of the interface.
> 

WTH?  My (utterly comedic chase-crap-around-the-tree) brightness script
was:

(
0 sh -c "echo $1 > /proc/acpi/sony/brightness"
0 sh -c "echo $1 > /proc/acpi/sony/brightness_default"
0 sh -c "echo $1 > /sys/class/backlight/sony/brightness"
0 sh -c "echo $1 > /sys/class/backlight/thinkpad_screen/brightness"
) 2>/dev/null

And yes, I had an rc.local command which assumed that 7 (later 8) is max
brightness.

You cannot seriously tell me that if we are to change this range from 0-8
up to 0-100 then this is not a backwards-incompatible change in
semantics.

My /sys/class/backlight/ directory is presently empty.  Rather than trying
to find out why, I think I'll just collapse in laughter.

Guys, sort it out, please.

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