Re: [PATCH] [RESEND] Add Dell laptop backlight brightness display

[Pavel Machek <pavel@ucw.cz>]

Hi!
On Út 07-02-06 13:55:02, Matthew Garrett wrote:
> On Tue, Feb 07, 2006 at 01:37:06PM +0000, Richard Purdie wrote:
> > On Tue, 2006-02-07 at 13:23 +0000, Matthew Garrett wrote:
> > > Would you be open to adding generic support for displaying separate AC 
> > > and DC brightnesses? Making it driver specific leaves the potential for
> > > inconsistencies.
> > 
> > The problem is that AC or DC is not a generic property of backlights but
> > specific to your problematic hardware case. You're going to have a to
> > find a way to tell if its running on AC or not to report the right value
> > in the manner the class requires.
> 
> Cases rather than case, sadly. Determining whether the hardware is on AC 
> or not tends to be much more awkward than you'd think. On HPs, it seems 
> to be done by making a specific call to the embedded controller. This is 
> very model specific, whereas the brightness values aren't. It's also 
> likely to go horribly wrong if the hardware is trying to access the 
> embedded controller at the same time. Realistically, it's impossible 
> without making the driver depend on ACPI and exporting acpi_ac_get_state 
> from the ACPI layer, which would be a shame since the rest of the 
> functionality isn't ACPI dependent at all.

Depending on acpi does not seem that bad. And exporting
acpi_ac_get_state is probably good idea for other reasons, too. (Look
how powernow-k8 does it; it needs pretty reliable AC/DC info.)
								Pavel
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