From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lee Jones Subject: Re: [PATCHv2] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero Date: Thu, 9 Jun 2016 14:51:25 +0100 Message-ID: <20160609135125.GA2385@dell> References: <1465294429-8570-1-git-send-email-LW@KARO-electronics.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <1465294429-8570-1-git-send-email-LW@KARO-electronics.de> Sender: linux-pwm-owner@vger.kernel.org To: Lothar =?iso-8859-1?Q?Wa=DFmann?= Cc: Jean-Christophe Plagniol-Villard , Jingoo Han , Thierry Reding , Tomi Valkeinen , linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org, Marcel Ziswiler , Ian Campbell , Kumar Gala , Mark Rutland , Pawel Moll , Rob Herring , devicetree@vger.kernel.org List-Id: devicetree@vger.kernel.org On Tue, 07 Jun 2016, Lothar Wa=C3=9Fmann 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-lif= e > examples). > Thus brightness =3D=3D 0 does not necessarily mean that the PWM outpu= t > will be inactive. > Check for 'duty_cycle =3D=3D 0' rather than 'brightness =3D=3D 0' to = decide > whether to disable the PWM. >=20 > Signed-off-by: Lothar Wa=C3=9Fmann > --- > Changes wrt. v1: > - update binding docs to reflect the change >=20 > .../devicetree/bindings/leds/backlight/pwm-backlight.txt | 9= ++++++--- > drivers/video/backlight/pwm_bl.c | 4= ++-- > 2 files changed, 8 insertions(+), 5 deletions(-) >=20 > diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-bac= klight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backl= ight.txt > index 764db86..95fa8a9 100644 > --- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.= txt > +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.= txt > @@ -4,10 +4,13 @@ Required properties: > - compatible: "pwm-backlight" > - pwms: OF device-tree PWM specification (see PWM binding[0]) > - brightness-levels: Array of distinct brightness levels. Typicall= y these > - are in the range from 0 to 255, but any range starting at 0 wi= ll do. > + are in the range from 0 to 255, but any range will do. > The actual brightness level (PWM duty cycle) will be interpola= ted > - from these values. 0 means a 0% duty cycle (darkest/off), whil= e the > - last value in the array represents a 100% duty cycle (brightes= t). > + from these values. 0 means a 0% duty cycle, while the highest = value in > + the array represents a 100% duty cycle. > + The range may be in reverse order (starting with the maximum d= uty cycle > + value) to create a PWM signal with the 100% duty cycle represe= nting > + minimum and 0% duty cycle maximum brigthness. > - default-brightness-level: the default brightness level (index in= to the > array defined by the "brightness-levels" property) > - power-supply: regulator for supply voltage > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlig= ht/pwm_bl.c > index b2b366b..80b2b52 100644 > --- a/drivers/video/backlight/pwm_bl.c > +++ b/drivers/video/backlight/pwm_bl.c > @@ -103,8 +103,8 @@ static int pwm_backlight_update_status(struct bac= klight_device *bl) > if (pb->notify) > brightness =3D pb->notify(pb->dev, brightness); > =20 > - if (brightness > 0) { > - duty_cycle =3D compute_duty_cycle(pb, brightness); > + duty_cycle =3D compute_duty_cycle(pb, brightness); > + if (duty_cycle > 0) { How does this work in the aforementioned: "The range may be in reverse order" =2E.. case? Surely when duty_cycle is when the screen should be at it'= s brightest? Wouldn't it confuse the user if they turn their brightness *up* and the screen goes *off*? > pwm_config(pb->pwm, duty_cycle, pb->period); > pwm_backlight_power_on(pb, brightness); > } else --=20 Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org =E2=94=82 Open source software for ARM SoCs =46ollow Linaro: Facebook | Twitter | Blog