linux-kernel - Re: [PATCH] thinkpad-acpi: fix return value of volume callbacks

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Date:	Thu, 25 Feb 2010 21:30:56 -0300
From:	Henrique de Moraes Holschuh <hmh@....eng.br>
To:	Clemens Ladisch <clemens@...isch.de>
Cc:	ibm-acpi-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] thinkpad-acpi: fix return value of volume callbacks

On Tue, 23 Feb 2010, Clemens Ladisch wrote:
> Henrique de Moraes Holschuh wrote:
> > On Mon, 22 Feb 2010, Clemens Ladisch wrote:
> > > Fix up the volume status setting functions to return a non-zero value if
> > > the control value has changed, so that the ALSA framework can correctly
> > > generate control change notifications.
> > 
> > Please explain...
> 
> ALSA sends notifications to all mixer application when the value of
> any mixer control has changed.  To be able to avoid sending them for
> controls that did not actually change, it uses the return value of the
> .put callback: 0 means the control value did not change; 1 means it has
> changed (or might have changed), and a notification is to be sent.
> <http://www.alsa-project.org/~tiwai/writing-an-alsa-driver/ch06s05.html#control-interface-callbacks-put>

I am looking at it.  I think I had it like that on purpose, to trigger an
OSD when a volume-related hotkey is pressed even if it doesn't change the
state (mute when already mute, vol down when already at minimum, etc).

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh
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