Re: [PATCH] radeon: Expose backlight class device for legacy LVDSencoder

[Matthew Garrett]

On Wed, Sep 08, 2010 at 12:58:32PM -0400, Alex Deucher wrote:

> The only problem with this is that not all oems use the internal
> backlight controller; systems that don't need to use the acpi methods.

That's why we expose the backlight type. Userspace should use the acpi 
or platform mechanism when available, with this being a last-ditch 
fallback.

>  On atombios systems there is a bit in the
> ATOM_FIRMWARE_CAPABILITY_ACCESS struct in the FirmwareInfo data table
> to determine whether the backlight is controlled by the GPU or some
> external mechanism.  Combios may have something similar.  If the
> backlight is controlled via the GPU, it can be adjusting using the
> atom OutputControl and TransmitterControl control tables depending on
> the GPU family.  However, if the driver chooses to control the
> backlight itself, it needs to set the appropriate bit in the bios
> scratch regs to tell the firmware not to attempt to change the
> backlight itself.

If there's support for probing this more reliably then I'm all for that, 
but I'm not keen on taking over control if the BIOS has previous 
asserted it.

-- 
Matthew Garrett | mjg59@xxxxxxxxxxxxx
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/