Re: [RFC PATCH 1/5] ACPI video: check the return value of acpi_video_device_lcd_get_level_current

[Thomas Renninger <trenn@suse.de>]

On Wednesday 11 March 2009 14:04:32 Matthew Garrett wrote:
> On Wed, Mar 11, 2009 at 01:56:00PM +0100, Thomas Renninger wrote:
> 
> > (BTW, I recently saw a BIOS with _BCQ function. They said they are going to 
> > fix it, but it may be more widespread, e.g. this also is often the case 
> > (missing _BQC) on Samsung). I found it by luck disassembling and 
> > recompiling the DSDT, a runtime warning would be nice (if it does not 
> > already exist).
> 
> It's not that uncommon - there's a few machines with _BCQ. I actually 
> thought we handled it already, but it seems not. Just adding a cap._BCQ 
> and using it if there's no _BQC sounds like a safe idea.
As said, the current brightness must be initialized if there is
no _BQC and Rui seem to have been removed that.

Also a:
printk (KERN_WARN FW_BUG PREFIX "ACPI brightness control misses _BQC function\n");
should be added.
Rui, if you are there already, do you mind to add such test.
I found by pure luck that a vendor mixed up
_BQC and _BCQ by getting one single warning recompiling the DSDT:
"_BCQ not a predefined function" (or similar). They are now adding it,
but a warning is appropriate IMO in _BQC missing case.
Not adding _BQC and doing brightness switching through ACPI brightness
functions is a really bad idea in general.

    Thomas