linux-kernel - Re: Backlight device class redesign

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Message-ID: <1259827274.27069.50.camel@rzhang1-desktop>
Date:	Thu, 03 Dec 2009 16:01:14 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	Rafał Miłecki <zajec5@...il.com>
Cc:	Linux ACPI <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Richard Purdie <rpurdie@...ys.net>
Subject: Re: Backlight device class redesign

On Mon, 2009-11-30 at 04:09 +0800, Rafał Miłecki wrote:
> W dniu 28 listopada 2009 01:30 użytkownik Rafał Miłecki
> <zajec5@...il.com> napisał:
> > As discussed in http://marc.info/?t=124947671300008&r=1&w=2 we need to
> > redesign our backlight device class.
> 
> I was trying to make it work this way:
> 1. Everytime register request comes, look for backlight_display with given name.
> 1. A. If needed, create new backlight_display
> 2. Add new device to devices list of backlight_display
> 3. Find best device on devices list of backlight_display
> 4. Register if under /sys/class/backlight/name_of_display
> 
> This didn't work because of registering only the best device. Look at
> this code in drivers/acpi/video.c:
> 

> device->backlight = backlight_device_register(name,
>     NULL, device, &acpi_backlight_ops);
> (...)
> result = sysfs_create_link(&device->backlight->dev.kobj,
>     &device->dev->dev.kobj, "device");
> 
IMO, we should create one device for one display.
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.

thanks,
rui

> It expects device to be registered (have dev.kobj) after calling
> backlight_device_register.
> 
> So in summary we just can not do lazy registration. Every device
> passed to backlight_device_register has to be registered in that
> function or never.
> 
> So I think we have to register every device and just keep symlink
> /sys/class/backlight/display_name pointing best device. We could
> register devices in
> 1) /sys/class/backlight/.devicename (hidden)
> 2) some /sys/class/internal-usage/devicename
> 
> Do you agree on this?
> 


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