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

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Message-ID: <5267B442.5090203@gmail.com>
Date:	Wed, 23 Oct 2013 19:34:26 +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 06:58 PM, Thierry Reding wrote:
> On Wed, Oct 23, 2013 at 06:46:17PM +0800, Mark Zhang wrote:
>> 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?
> 
> No, there's no substitution for that. .check_fb() is used to verify that
> a backlight device is associated with a framebuffer device. There are
> better ways to check for that with DT, although nothing has been merged
> into mainline yet.
> 

Okay, thanks for the explanation.

Mark
> Thierry
> 
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