linux-kernel - Re: [ibm-acpi-devel] [PATCH] video: backlight: Remove backlight sysfs uevent

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Date:	Sun, 24 Nov 2013 01:02:57 +0000
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	linux-fbdev@...r.kernel.org,
	'Kyungmin Park' <kmpark@...radead.org>, kay@...y.org,
	Jingoo Han <jg1.han@...sung.com>,
	'Henrique de Moraes Holschuh' <ibm-acpi@....eng.br>,
	linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org,
	ibm-acpi-devel@...ts.sourceforge.net,
	'Richard Purdie' <rpurdie@...ys.net>
Subject: Re: [ibm-acpi-devel] [PATCH] video: backlight: Remove backlight
 sysfs uevent

On Sat, Nov 23, 2013 at 10:40:15PM -0200, Henrique de Moraes Holschuh wrote:
> On Fri, 22 Nov 2013, Matthew Garrett wrote:
> > We have userspace that relies on uevents of type 
> > BACKLIGHT_UPDATE_HOTKEY. I don't know that we have userspace that relies 
> > on uevents of type BACKLIGHT_UPDATE_SYSFS.
> 
> Any OSD application would have to rely on both uevent types, or it is broken
> (and to test that, just write a level to sysfs and watch the OSD app fail to
> tell you about the backlight level change...)

Right, OSDs are supposed to respond to keypresses, not arbitrary changes 
of backlight. If the user's just echoed 8 into brightness, they know 
they set the brightness to 8 - they don't need an OSD to tell them that. 
BACKLIGHT_UPDATE_HOTKEY is when the firmware itself has changed the 
brightness in response to a keypress, and so reporting the keypress 
would result in additional backlight changes.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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