Re: [PATCH] ACPI: disable the ACPI backlight control on laptops with buggy _BCL methods

[Matthew Garrett <mjg59@srcf.ucam.org>]

On Thu, Jan 08, 2009 at 02:32:01PM +0800, Zhang Rui wrote:
> > Why? These all seem to behave consistently, so I can't see any problem 
> > with us simply adding support for this varient.
> the problem is that the ACPI backlight I/F and the platform I/F coexists
> before commit c3d6de698c84efdbdd3781b7058bcc339ab43da8 applied, and the
> platform I/F is preferred.

For the machines you've looked at - we don't know if that's true for all 
hardware that behaves this way.

> in bug 12249 and 12037,
> 1. the first two elements in _BCL are NOT the backlight levels when the
> platform is on AC or battery.

We can detect that easily and adjust behaviour accordingly.

> 2. _BQC returns the index of the current brightness in _BCL package
> rather than the value, which surely breaks the ACPI video driver.

And again, we can handle that.

> 2. every elements in the _BCL package is not a percentage of the maximum
> brightness, which is also a violation of ACPI spec.

This seems pretty irrelevant - nothing in the code depends on these 
being percentages.

> yes, we can make the ACPI backlight control work by using customized
> DSDT. But that's not the fix neither. I don't have any better ideas than
> disable them.

Just fix up video.c to handle these cases.

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