linux-kernel - Re: [PATCH] backlight: pwm_bl: disable PWM when 'duty

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160607084907.14ffdc03@ipc1.ka-ro>
Date:	Tue, 7 Jun 2016 08:49:07 +0200
From:	Lothar Waßmann <LW@...O-electronics.de>
To:	Tomi Valkeinen <tomi.valkeinen@...com>
Cc:	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	Thierry Reding <thierry.reding@...il.com>,
	<linux-fbdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-pwm@...r.kernel.org>
Subject: Re: [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is
 zero

Hi,

On Mon, 6 Jun 2016 15:02:21 +0300 Tomi Valkeinen wrote:
> Hi,
> 
> On 06/06/16 13:44, Lothar Waßmann wrote:
> > 'brightness' is usually an index into a table of duty_cycle values,
> > where the value at index 0 may well be non-zero
> > (tegra30-apalis-eval.dts and tegra30-colibri-eval-v3.dts are real-life
> > examples).
> > Thus brightness == 0 does not necessarily mean that the PWM output
> > will be inactive.
> > Check for 'duty_cycle == 0' rather than 'brightness == 0' to decide
> > whether to disable the PWM.
> 
> The binding doc does say:
> 
>   - brightness-levels: Array of distinct brightness levels. Typically these
>       are in the range from 0 to 255, but any range starting at 0 will do.
>       The actual brightness level (PWM duty cycle) will be interpolated
>       from these values. 0 means a 0% duty cycle (darkest/off), while the
>       last value in the array represents a 100% duty cycle (brightest).
> 
So, what should I do, when I need a range of levels that doesn't start
at 0? E.g. if the brightness is inverse proportional to the PWM duty
cycle.



Lothar Waßmann