Re: [PATCH] toshiba_acpi: fingers off backlight if video.ko is serving this functionality

Andrey Borzenkov
2008-11-13T04:58:19Z

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On Thursday 13 November 2008, Matthew Garrett wrote:
> On Wed, Nov 12, 2008 at 05:41:35PM -0600, Thomas Renninger wrote:
> > On Tuesday 11 November 2008 02:04:15 pm Len Brown wrote:
> > > so when i apply this patch, i get fewer brightness levels.
> > > I prefer to have all 8 brightness levels.
> >
> > The patch from Andrey is correct.
> > Looks like all, the ordinary user needs, and probably the way it works on a
> > plain Vista OS is there: off, battery, full level.
> > You can still use the boot param for your specific needs:
> > acpi_display_output=vendor
>
> The Toshiba BIOSes I've looked at all implement the ACPI code on top of
> the legacy interface. Do you have examples where that's not the case? If
> not, I don't see the harm in exposing both.
>

See http://marc.info/?l=linux-acpi&m=122068736714509&w=2 and related thread.

Basically situation is as follows:

- since some time both video and toshiba_acpi attempt to drive brightness

- on some (many? most?) Toshiba laptops standard-conform ACPI implementation
is inferior in that it is less fine grained than HCI one

- exposing two knobs for the *same* thing confuses user level tools; you never
know which one is used and they compete behind your back

- so effectively on Toshiba you *must* use acpi_brightness=vendor or use
similar default in video_detect.c

- in which case we may just as well play it consistent and add support for
video/vendor switch to toshiba_acpi in case someone does want to use ACPI knob
(be it even only for testing).

So the actual question is - how we detect Toshiba and default to vendor
brightness control?

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