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

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Message-ID: <20080122123923.GC15490@khazad-dum.debian.net>
Date:	Tue, 22 Jan 2008 10:39:23 -0200
From:	Henrique de Moraes Holschuh <hmh@....eng.br>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	Zhang Rui <rui.zhang@...el.com>, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org, len.brown@...el.com
Subject: Re: [PATCH] Rationalise ACPI backlight implementation

On Tue, 22 Jan 2008, Matthew Garrett wrote:
> On Tue, Jan 22, 2008 at 04:33:29PM +0800, Zhang Rui wrote:
> > I have no obvious objection on either of these two proposals.
> > But one thing to mention is that
> > both of these two patches is written on the assumption that the
> > brightness levels listed in _BCL method are in ascending order, while
> > this is not stated in the ACPI spec.
> > Is this a problem?
> 
> The driver already makes that assumption, and it's implicit in the spec.

Actually, no, it is not implicit.  The spec clearly states that the
brightness values will be cycled through the ones given by that list.  It is
implicit that brightness up actions will cycle through the list in order,
and brightness down will cycle through the list in reverse order.

If a vendor where to decide to place the most used brightness values in the
beginning of the list, and the rest of it later, he would be allowed to do
so.  Nobody was weird enough to do it yet though, AFAIK.

-- 
  "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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