linux-kernel - Re: [PATCH 1/4] pwm_backlight: Fix PWM levels support in non DT case

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Date:	Tue, 29 Jan 2013 09:17:04 +0100
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Thierry Reding <thierry.reding@...onic-design.de>
CC:	Richard Purdie <rpurdie@...ys.net>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Landley <rob@...dley.net>,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<devicetree-discuss@...ts.ozlabs.org>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-fbdev@...r.kernel.org>
Subject: Re: [PATCH 1/4] pwm_backlight: Fix PWM levels support in non DT case

On 01/28/2013 10:01 PM, Thierry Reding wrote:
> On Tue, Jan 22, 2013 at 02:39:53PM +0100, Peter Ujfalusi wrote:
>> It is expected that board files would have:
>> static unsigned int bl_levels[] = { 0, 50, 100, 150, 200, 250, };
>>
>> static struct platform_pwm_backlight_data bl_data = {
>> 	.levels = bl_levels,
>> 	.max_brightness = ARRAY_SIZE(bl_levels),
>> 	.dft_brightness = 4,
>> 	.pwm_period_ns = 7812500,
>> };
>>
>> In this case the max_brightness would be out of range in the levels array.
>> Decrement the received max_brightness in every case (DT or non DT) when the
>> levels has been provided.
> 
> What's wrong with specifying .max_brightness = ARRAY_SIZE(bl_levels) - 1
> instead?

There is nothing wrong with that either but IMHO it is more natural for board
files to use just ARRAY_SIZE(bl_levels). In this way the handling of
data->max_brightness among non DT and DT booted kernel is more uniform in the
driver itself.
Right now all board files are using only the .max_brightness to specify the
maximum value, I could not find any users of .levels in the kernel.

-- 
Péter
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