linux-kernel - Re: Backlight device class redesign

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Message-ID: <1259891448.27069.83.camel@rzhang1-desktop>
Date:	Fri, 04 Dec 2009 09:50:48 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	Rafa?? Mi??ecki <zajec5@...il.com>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Richard Purdie <rpurdie@...ys.net>,
	Matthew Garrett <mjg59@...f.ucam.org>
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?
we can use something like DEFAULT_ACPI_DISPLAY/DEFAULT_PLATFORM_DISPLAY
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?

thanks,
rui

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