linux-kernel - Re: [patch] added brightness feature to lcd class.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 09 Nov 2009 23:35:05 +0000
From:	Richard Purdie <rpurdie@...ux.intel.com>
To:	InKi Dae <daeinki@...il.com>
Cc:	linux-fbdev-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, Kyungmin Park <kmpark@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Machek <pavel@....cz>
Subject: Re: [patch] added brightness feature to lcd class.

On Mon, 2009-11-02 at 17:50 +0900, InKi Dae wrote:
> This patch adds brightness feature to lcd class.
> (kernel/driver/video/backlight/lcd.c)
> 
> In the past, most of the lcd panels for embedded system was TFT-LCD
> Panel needing backlight device.
> But now AMOLED LCD Panel appeared so we should consider brightness
> control for AMOLED Panel.
> 
> For the time being, I used backlight fake driver for brightness
> control of AMOLED LCD Panel.
> But this way is not good, so I propose to add brightness feature to lcd class.
> 
> For this, I attached patch file and if my proposal is approved
> Then I will send s6e63m0 and tl2796 AMOLED lcd panel driver based on
> lcd class modified soon.

Pavel has a good point but let me try and explain it differently.

The point of the backlight class is to expose a backlight brightness
control to userspace in a consistent well defined way. Anyone wishing to
write a piece of software to control the brightness of a backlight then
only needs to support *one* interface.

It is entirely accepted and normal that multiple "class" devices may
appear in userspace for one piece of physical hardware.

Your patch duplicates a userspace API and means any backlight
application would have to look for *two* different interfaces. This is
unacceptable.

Why can't your driver just register a backlight interface and an LCD
interface? I'd imagine your backlight and LCD can be powered on/off
separately too.

Please also cc: the backlight/lcd maintainer (me) on backlight/lcd
patches in future.

Andrew: Can you drop that patch from -mm please as I'm not convinced we
need two backlight brightness interfaces around...

Cheers,

Richard

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/