Re: Re: Backlight support

On Tue, 30 Nov 2004 16:28:26 -0000
"Richard Purdie" [off-list ref] wrote:

I think the above patch was nearly there. The issues seemed to be with
the method of associating framebuffer devices with their backlights.
I've come up with a solution to that problem (see below) so that code
can be removed from that patch and that should make it acceptable for
mainstream kernel inclusion.

I confirm that the solution you proposed is quite suitable for the job.
I've already modified the lcd/backlight subsystem, and I have a few
comments;

a) First of all, the implementation of your idea looks quite well
(it's simpler and cleaner than the old method), although initially I
didn't like it (mea culpa). I have removed a lot of now unneeded code
from b/l support, and also it removes a lot of lcd/backlight
maintainance code from the framebuffer drivers(pxafb, sa11xxfb,
mq11xxfb). Last but not least, it removed the class_find_device()
function that was the sticking point in the discussion with gkh.

b) No modification is needed to the existing lcd/backlight drivers
(there are about ten of them in hh.org cvs). I've added just one more
function pointer in the lcd_properties and backlight_properties to a
function that gets a fb_info and examinates if it is the
framebuffer to which the lcd/backlight is attached to. If the function
is NULL, the framebuffer is considered to match (since in PDAs there's
only one framebuffer, this perfectly fits already existing drivers).

c) There's a problem though; if someone will REALLY want to inspect
the fb_info, it would be very helpful to be able to deduce somehow the
'struct device' associated with the framebuffer, since the fb_info
itself doesn't contain anything more useful than the current resolution
and pixel format. Knowing the device (and its position on the parent
bus) the backlight/lcd driver will know exactly what to look at. I've
seen some semi-commented code in 2.6.10 which tells me there are plans
to integrate the fb_info into the sysfs (and, therefore, to add a
class_device somewhere in the fb_info); this will allow also the b/l
drivers to find the associated framebuffer device. Am I correct in my
assumptions?

As soon as handhelds.org will be up, I'll be able to test the code and,
once it'll work, I'll send a patch to linux-fbdev-devel@.

-- 
Greetings,
   Andrew


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