From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lothar =?UTF-8?B?V2HDn21hbm4=?= Date: Tue, 07 Jun 2016 06:49:07 +0000 Subject: Re: [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero Message-Id: <20160607084907.14ffdc03@ipc1.ka-ro> List-Id: References: <1465209896-10319-1-git-send-email-LW@KARO-electronics.de> <5755664D.5070109@ti.com> In-Reply-To: <5755664D.5070109@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: Tomi Valkeinen Cc: Jean-Christophe Plagniol-Villard , Jingoo Han , Lee Jones , Thierry Reding , linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org 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