linux-kernel - Re: How to set fops in "struct platform_pwm_backlight

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Message-ID: <20131023080002.GB7404@ulmo.nvidia.com>
Date:	Wed, 23 Oct 2013 10:00:03 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Mark Zhang <nvmarkzhang@...il.com>
Cc:	rpurdie@...ys.net, jg1.han@...sung.com,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	tomi.valkeinen@...com, linux-pwm@...r.kernel.org,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: How to set fops in "struct platform_pwm_backlight_data"?

On Wed, Oct 23, 2013 at 10:16:24AM +0800, Mark Zhang wrote:
> On 10/22/2013 08:49 PM, Thierry Reding wrote:
> > On Tue, Oct 22, 2013 at 04:55:09PM +0800, Mark Zhang wrote:
> >> On 10/22/2013 03:24 PM, Thierry Reding wrote:
> >>> On Fri, Oct 18, 2013 at 12:48:12PM +0800, Mark Zhang wrote:
> >> [...]
> >>>>>
> >>>>
> >>>> Okay, I just want to set the "notify" function pointer in "struct
> >>>> platform_pwm_backlight_data", because I want to tune the brightness
> >>>> value before the pwm-bl sets the brightness to hardware. I don't know
> >>>> how to do that, unless we define the platform data explicitly.
> >>>
> >>> Okay, my question should have been what you need the functions for and
> >>> why you think you need them.
> >>>
> >>
> >> If I understanding you correctly, I suppose I've said that: "because I
> >> want to tune the brightness value before the pwm-bl sets the brightness
> >> to hardware".
> > 
> > Why do you want to tune the brightness value? What are you trying to
> > achieve?
> > 
> 
> Oh, Tegra has a feature named PRISM(aka SmartDimmer). It changes the
> color value to make the display looks bright so that we can reduce the
> backlight brightness to save power. So everytime PRISM is triggered, we
> call "backlight_update_status", then in the "notify" callback, we change
> the brightness value which pwm-bl provides by considering the PRISM
> compensations.

If you automatically call backlight_update_status() everytime PRISM
gives you new data, can't you just pass the correct value in in the
first place so that you don't have to tweak it in the .notify()
callback?

Thierry

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