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

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Date:	Wed, 23 Oct 2013 18:46:17 +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 06:36 PM, Mark Zhang wrote:
> 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().
>>
> 
> Okay, anyway, I got the idea. Actually it's simpler. :)
> I'm just curious that if we can do that in this way, why we need
> "notify" anymore?

Oh, by the way, how about "check_fb" fops? Is there some kind of
substitution as well? I mean, if I wanna set "check_fb" and also want to
define the backlight device via DT, is there a way to do that?

Mark
> 
> Mark
>> Thierry
>>
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