[Intel-gfx] [RFC] [intel-gfx] :The backlight issue when KMS is used

yakui_zhao yakui.zhao at intel.com
Tue Apr 7 09:25:23 CEST 2009

On Tue, 2009-04-07 at 13:57 +0800, Matthew Garrett wrote:
> On Tue, Apr 07, 2009 at 11:45:11AM +0800, yakui_zhao wrote:
> > On Sat, 2009-04-04 at 00:29 +0800, Matthew Garrett wrote:
> > > Right. I'd imagine it as i915 loading and calling is_acpi_backlight(). 
> > > If that returns false, it should register a backlight device and also a 
> > > notifier. If a machine-specific platform device (like thinkpad_acpi or 
> > > dell_laptop or whatever) then loads, i915 should unregister its driver 
> > > and leave it up to the machine-specific one. The DDX would then use the 
> > > backlight device under all circumstances.
> > A good idea. When there is no generic ACPI backlight I/F(_BQC/_BCL/_BCM)
> > or platform backlight I/F, a new baclight I/F(using platform I2C
> > command) will be registered in i915 driver.    
> > Will this new backlight I/F be registered in both UMS/KMS mode?
> No, since in UMS mode the X server handles the backlight registers.
If so, there is no change about the backlight flowchart in UMS mode.

And only when the KMS mode is used, a new backlight I/F is registered.
> > But if we do so, it seems that we have to solve the dependency issue
> > among acpi_video, i915 and platform driver. 
> >    For example: I915 driver is loaded firstly and the interface will be
> > registered. But after the acpi video driver/platform driver is loaded,
> > how to send the notification event that i915 should unregister its
> > interface? If the interface is unregistered, we will have to consider
> > the arbiter order.
> The acpi case is uninteresting - acpi_video_backlight_support() doesn't 
> require the acpi video driver. The platform driver case is more 
> interesting, but the easiest solution is probably to add a notifier 
> chain for backlight device add and have i915 unregister when a platform 
> device registers.
Yes. We will have to create the communication channel between backlight
device and i915 driver. And when a backlight I/F is registered, we will
have to check whether the backlight I/F in 915 should be unregistered. 
Does this make the problem complex? 
> I'm not sure what you mean by arbiter order?
What I said is which backlight I/F should be selected if there exist
multiple backlight I/F?

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