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Date:	Fri, 04 Dec 2009 09:50:48 +0800
From:	Zhang Rui <>
To:	Henrique de Moraes Holschuh <>
Cc:	Rafa?? Mi??ecki <>,
	Linux ACPI <>,
	Linux Kernel Mailing List <>,
	Richard Purdie <>,
	Matthew Garrett <>
Subject: Re: Backlight device class redesign

On Thu, 2009-12-03 at 18:52 +0800, Henrique de Moraes Holschuh wrote:
> On Thu, 03 Dec 2009, Zhang Rui wrote:
> > For example, device /sys/class/backlight/panel0 is created the first
> > time a backlight_ops for this display is registered.
> > And create the symbol link from the backlight class device to "physical
> > device" (device that invokes backlight_device_register) in the backlight
> > class device driver, if we really need it.
> > Remove and recreate a link pointing to the new physical device when the
> > backlight mode is changed.
> FWIW, I agree the above solution is simple enough and quite good enough.
> I just have absolutely _NO_ idea whatsoever how a platform driver can ask
> the PCI or APCI layer "where is the video device driving the LVDS panel so
> that I can bind to it"...
well. this is the question I want to ask. :)

IMO, if we want to create one device for one display, we must have a
unique ID for each display and the ID must be generic enough so that
both ACPI & platform & graphics driver can understand it.

ACPI&platform drivers have no idea about the display info it's bind to.
But they're always used to control the integrated panel, no?
which stands for the integrated LVDS panel, which can also be understood
by the graphics driver.

ACPI video driver -->ACPI_DISPLAY-->|
platform driver->PLATFORM_DISPLAY-->|--->/sys/class/backlight/panel0
          |-->integrated panel----->|
graphics  |-->TV------------------->|--->/sys/class/backlight/tv0
          |-->external LCD--------->|--->...

I'm not a graphics guy so I don't if there are any other ways to control
the TV/external LCD device, if yes, they can use something else as the
unique ID, say EDID, right?


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