From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755833Ab2I0VdN (ORCPT ); Thu, 27 Sep 2012 17:33:13 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:36000 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755540Ab2I0VdK (ORCPT ); Thu, 27 Sep 2012 17:33:10 -0400 Date: Thu, 27 Sep 2012 14:33:09 -0700 From: Andrew Morton To: "Philip, Avinash" Cc: , , , , , , , , , , , Subject: Re: [PATCH v3] pwm_backlight: Add device tree support for Low Threshold Brightness Message-Id: <20120927143309.02614908.akpm@linux-foundation.org> In-Reply-To: <1348670827-5720-1-git-send-email-avinashphilip@ti.com> References: <1348670827-5720-1-git-send-email-avinashphilip@ti.com> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 26 Sep 2012 20:17:07 +0530 "Philip, Avinash" wrote: > Some back lights perform poorly when driven by a PWM with a short > duty-cycle. For such devices, the low threshold can be used to specify a > lower bound for the duty-cycle and should be chosen to exclude the > problematic range. > > Add device tree probing support for lth_brightness putting > low-threshold-brightness as optional property. > > ... > > --- a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt > +++ b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt > @@ -14,6 +14,15 @@ Required properties: > Optional properties: > - pwm-names: a list of names for the PWM devices specified in the > "pwms" property (see PWM binding[0]) > + - low-threshold-brightness: brightness threshold low level. Low threshold > + brightness set to value so that backlight present on low end of > + brightness. > + Some panels, backlight would absent if duty percentage of PWM wave is less > + than certain level (say 20%). By setting low-threshold-brightness to a > + value above (percentage of brightness-levels max) 50 (20% of 255, if 255 > + is max). On setting low-threshold-brightness, range of brightness-levels > + is calculated in a region of low-threshold-brightness to brightness-levels > + max. hoo boy, that's hard to follow. How does this look? --- a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt~pwm_backlight-add-device-tree-support-for-low-threshold-brightness-fix +++ a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt @@ -14,15 +14,15 @@ Required properties: Optional properties: - pwm-names: a list of names for the PWM devices specified in the "pwms" property (see PWM binding[0]) - - low-threshold-brightness: brightness threshold low level. Low threshold - brightness set to value so that backlight present on low end of - brightness. - Some panels, backlight would absent if duty percentage of PWM wave is less - than certain level (say 20%). By setting low-threshold-brightness to a - value above (percentage of brightness-levels max) 50 (20% of 255, if 255 - is max). On setting low-threshold-brightness, range of brightness-levels - is calculated in a region of low-threshold-brightness to brightness-levels - max. + - low-threshold-brightness: brightness threshold low level. Sets the lowest + brightness value. + On some panels the backlight misbehaves if the duty cycle percentage of the + PWM wave is less than a certain level (say 20%). In this example the user + can set low-threshold-brightness to a value above 50 (ie, 20% of 255), thus + preventing the PWM duty cycle from going too low. + On setting low-threshold-brightness the range of brightness levels is + calculated in the range low-threshold-brightness to the maximum value in + brightness-levels, described above. [0]: Documentation/devicetree/bindings/pwm/pwm.txt Also, I'm wondering if we really needed a new property - couldn't one do this simply by setting brightness-levels to 50..255?