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

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Message-ID: <5267A582.9070504@gmail.com>
Date:	Wed, 23 Oct 2013 18:31:30 +0800
From:	Mark Zhang <nvmarkzhang@...il.com>
To:	Thierry Reding <thierry.reding@...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 10/23/2013 05:09 PM, Thierry Reding wrote:
> On Wed, Oct 23, 2013 at 04:49:29PM +0800, Mark Zhang wrote:
>> On 10/23/2013 04:00 PM, Thierry Reding wrote:
>>> 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?
>>
>> OK, how to do that? -- "pass the correct value in in the first place"?
> 
> Well, if you call backlight_update_status(), then you can pass in a
> brightness value, right? You usually do that by setting the backlight's
> props.brightness field.
> 
> So when PRISM gives you new data, you could just read out the current
> brightness, compute the new one based on the current one and the PRISM
> data, set the props.brightness field to that value and then call
> backlight_update_status().
> 

The param of "backlight_update_status" is "struct backlight_device *".
So you mean after I get a pointer of correct backlight device, just set
the brightness value I want to it's "props.brightness" directly?

I think the "struct backlight_device" should be opaque(although it's
definition is in include/linux/backlight.h, I know that), so it's better
not to touch it's member directly, that's why I wanna use that "notify"
callback.

Mark
> Thierry
> 
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