linux-kernel - Re: [PATCH] Added backlight driver for Acer Aspire 4736

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Message-ID: <1331640592.3485.50.camel@debian.Gayathri>
Date:	Tue, 13 Mar 2012 08:09:52 -0400
From:	Pradeep Subrahmanion <subrahmanion.pradeep@...il.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	rpurdie@...ys.net, FlorianSchandinat@....de,
	akpm@...ux-foundation.org, linux-fbdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Added backlight driver for Acer Aspire 4736

Before taking this approach , I had a look at the WMI interface.But I found from acer-acpi site that , the 4730 series 
is using new WMI interface which needs to be reverse engineered.
As far as  acpi interface is concerned , by default it is not at all causing any change in brightness.
When 'acpi_osi=Linux' was added to the boot grub config , the brightness control with hot key started to work .
But it was not changing to correct values. Increasing brightness after maximum level gives blank screen.

please find attached the acpidump output

On Mon, 2012-03-12 at 17:51 +0000, Matthew Garrett wrote:
> On Mon, Mar 12, 2012 at 11:12:17PM -0400, Pradeep Subrahmanion wrote:
> > Hi ,
> > 
> >   Brightness control was not  working on Acer Aspire 4736 using default ACPI interface.  acer-acpi also do not support 4730 series since it uses new WMI interface.
> > This driver adds brightness control by accessing the LBB PCI configuration register. This approach may also work on other laptops in 4730 series .But currently ,  it is only tested  for 
> > Aspire 4736. 
> 
> 1) If there's a WMI interface to brightness control, why not use that?
> 2) You're hitting a hardware resource that belongs to the i915 driver, 
> which may well cause problems.
> 3) Why does the ACPI interface not work? Can you attach the acpidump 
> output?
> 


View attachment "acpidump.txt" of type "text/plain" (227974 bytes)