linux-kernel - Re: [PATCH v4 1/4] backlight: introduce backlight_device

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Date:	Thu, 10 Oct 2013 12:53:02 +0800
From:	Aaron Lu <aaron.lu@...el.com>
To:	Jani Nikula <jani.nikula@...ux.intel.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	linux-acpi@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Daniel Vetter <daniel@...ll.ch>,
	Matthew Garrett <matthew.garrett@...ula.com>,
	Seth Forshee <seth.forshee@...onical.com>,
	Lee Chun-Yi <joeyli.kernel@...il.com>,
	Richard Purdie <rpurdie@...ys.net>,
	Igor Gnatenko <i.gnatenko.brain@...il.com>,
	Yves-Alexis Perez <corsac@...ian.org>,
	Felipe Contreras <felipe.contreras@...il.com>,
	Ben Jencks <ben@...ncks.net>,
	Steven Newbury <steve@...wbury.org.uk>,
	James Hogan <james@...anarts.com>,
	Kamal Mostafa <kamal@...onical.com>,
	Joerg Platte <jplatte@...sa.net>,
	Kalle Valo <kvalo@...rom.com>,
	Martin Steigerwald <Martin@...htvoll.de>,
	Jörg Otte <jrg.otte@...il.com>,
	Mike Galbraith <bitbucket@...ine.de>,
	platform-driver-x86@...r.kernel.org,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Henrique de Moraes Holschuh <hmh@....eng.br>
Subject: Re: [PATCH v4 1/4] backlight: introduce backlight_device_registered

On 10/10/2013 12:29 PM, Jani Nikula wrote:
> On Thu, 10 Oct 2013, Aaron Lu <aaron.lu@...el.com> wrote:
>> On 10/10/2013 08:25 AM, Rafael J. Wysocki wrote:
>>> On Tuesday, October 08, 2013 02:39:58 PM Aaron Lu wrote:
>>>> +bool backlight_device_registered(enum backlight_type type)
>>>> +{
>>>> +	bool found = false;
>>>> +	struct backlight_device *bd;
>>>> +
>>>> +	mutex_lock(&bd_list_mutex);
>>>> +	list_for_each_entry(bd, &bd_list_head, entry) {
>>>> +		if (bd->props.type == type) {
>>>> +			found = true;
>>>> +			break;
>>>> +		}
>>>> +	}
>>>
>>> Isn't it useful to be able to register more than one backlight device of the
>>> same type sometimes?
>>
>> I think so for some kind of computers. OTOH, the above function should
>> be enough for the problem we are solving here, if someday we need to
>> differentiate, we can enhance the code then.
> 
> Since both Baytrail and Haswell already have two backlight PWMs, this
> may be needed sooner than you think. But we shouldn't let that block

Do we need to differentiate which backlight PWM is registered to decide
if ACPI video backlight interface should be skipped? My understanding is
no.

Thanks,
Aaron

> fixing the more urgent issue we have now. So I'm fine with this. It
> doesn't prevent one from registering more than one device of the same
> type anyway.
> 
> BR,
> Jani.
> 
> 
> 

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