From: "Lothar Waßmann" <LW@KARO-electronics.de>
To: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>,
Jingoo Han <jingoohan1@gmail.com>,
Lee Jones <lee.jones@linaro.org>,
Thierry Reding <thierry.reding@gmail.com>,
<linux-fbdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<linux-pwm@vger.kernel.org>
Subject: Re: [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero
Date: Tue, 7 Jun 2016 08:49:07 +0200 [thread overview]
Message-ID: <20160607084907.14ffdc03@ipc1.ka-ro> (raw)
In-Reply-To: <5755664D.5070109@ti.com>
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
next prev parent reply other threads:[~2016-06-07 6:49 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-06 10:44 [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero Lothar Waßmann
2016-06-06 12:02 ` Tomi Valkeinen
2016-06-07 6:49 ` Lothar Waßmann [this message]
2016-06-07 8:02 ` Tomi Valkeinen
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