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

yakui_zhao yakui.zhao at intel.com
Tue Apr 7 05:45:11 CEST 2009

On Sat, 2009-04-04 at 00:29 +0800, Matthew Garrett wrote:
> On Fri, Apr 03, 2009 at 09:24:08AM -0700, Jesse Barnes wrote:
> > I'd rather not have a native kernel backlight property (i.e. a property
> > on the LVDS output) exposed at all.  I chatted with Matthew about this
> > a little, and I think the best thing to do would be to have the i915
> > driver register a backlight interface of its own if one doesn't already
> > exist (e.g. in the case of a platform specific i2c interface and no
> > ACPI backlight support).
> > 
> > We might have to hack the backlight class code a little to prevent
> > multiple registrations for the same device, but that shouldn't be too
> > hard.
> > 
> > Then whichever driver loads first (i915 or acpi video) would create a
> > backlight interface if it could, and the userspace driver could use it;
> > no need for new properties.
> 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?

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.
   Does this make the problem more complex?

Will this new backlight I/F be registered in UMS mode?

cc: Richard Purdie

Best regards.

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