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GET /api/patches/809723/?format=api
{ "id": 809723, "url": "http://patchwork.ozlabs.org/api/patches/809723/?format=api", "web_url": "http://patchwork.ozlabs.org/project/devicetree-bindings/patch/20170904153504.27963-2-enric.balletbo@collabora.com/", "project": { "id": 37, "url": "http://patchwork.ozlabs.org/api/projects/37/?format=api", "name": "Devicetree Bindings", "link_name": "devicetree-bindings", "list_id": "devicetree.vger.kernel.org", "list_email": "devicetree@vger.kernel.org", "web_url": "", "scm_url": "", "webscm_url": "", "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<20170904153504.27963-2-enric.balletbo@collabora.com>", "list_archive_url": null, "date": "2017-09-04T15:35:03", "name": "[RFC,1/2] dt-bindings: pwm-backlight: add brightness-levels-scale property", "commit_ref": null, "pull_url": null, "state": "changes-requested", "archived": true, "hash": "d509717682db4cffe8b704e1f2084b6ecd09cd4c", "submitter": { "id": 68184, "url": "http://patchwork.ozlabs.org/api/people/68184/?format=api", "name": "Enric Balletbo i Serra", "email": "enric.balletbo@collabora.com" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/devicetree-bindings/patch/20170904153504.27963-2-enric.balletbo@collabora.com/mbox/", "series": [ { "id": 1408, "url": "http://patchwork.ozlabs.org/api/series/1408/?format=api", "web_url": "http://patchwork.ozlabs.org/project/devicetree-bindings/list/?series=1408", "date": "2017-09-04T15:35:03", "name": "backlight: pwm_bl: support linear brightness to human eye", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/1408/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/809723/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/809723/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<devicetree-owner@vger.kernel.org>", "X-Original-To": "incoming-dt@patchwork.ozlabs.org", "Delivered-To": "patchwork-incoming-dt@bilbo.ozlabs.org", "Authentication-Results": "ozlabs.org;\n\tspf=none (mailfrom) smtp.mailfrom=vger.kernel.org\n\t(client-ip=209.132.180.67; helo=vger.kernel.org;\n\tenvelope-from=devicetree-owner@vger.kernel.org; receiver=<UNKNOWN>)", "Received": [ "from vger.kernel.org (vger.kernel.org [209.132.180.67])\n\tby ozlabs.org (Postfix) with ESMTP id 3xmDSS2gwlz9t2c\n\tfor <incoming-dt@patchwork.ozlabs.org>;\n\tTue, 5 Sep 2017 01:35:20 +1000 (AEST)", "(majordomo@vger.kernel.org) by vger.kernel.org via listexpand\n\tid S1753776AbdIDPfS (ORCPT\n\t<rfc822;incoming-dt@patchwork.ozlabs.org>);\n\tMon, 4 Sep 2017 11:35:18 -0400", "from bhuna.collabora.co.uk ([46.235.227.227]:46158 \"EHLO\n\tbhuna.collabora.co.uk\" rhost-flags-OK-OK-OK-OK) by vger.kernel.org\n\twith ESMTP id S1753880AbdIDPfQ (ORCPT\n\t<rfc822; devicetree@vger.kernel.org>); Mon, 4 Sep 2017 11:35:16 -0400", "from [127.0.0.1] (localhost [127.0.0.1])\n\t(Authenticated sender: eballetbo) with ESMTPSA id F2DFD265861" ], "From": "Enric Balletbo i Serra <enric.balletbo@collabora.com>", "To": "Lee Jones <lee.jones@linaro.org>,\n\tDaniel Thompson <daniel.thompson@linaro.org>,\n\tJingoo Han <jingoohan1@gmail.com>, Richard Purdie <rpurdie@rpsys.net>,\n\tJacek Anaszewski <jacek.anaszewski@gmail.com>,\n\tPavel Machek <pavel@ucw.cz>, Rob Herring <robh+dt@kernel.org>,\n\tMark Rutland <mark.rutland@arm.com>,\n\tDoug Anderson <dianders@google.com>, \n\tBrian Norris <briannorris@google.com>, Guenter Roeck <groeck@google.com>", "Cc": "linux-leds@vger.kernel.org, devicetree@vger.kernel.org,\n\tlinux-kernel@vger.kernel.org", "Subject": "[RFC 1/2] dt-bindings: pwm-backlight: add brightness-levels-scale\n\tproperty", "Date": "Mon, 4 Sep 2017 17:35:03 +0200", "Message-Id": "<20170904153504.27963-2-enric.balletbo@collabora.com>", "X-Mailer": "git-send-email 2.9.3", "In-Reply-To": "<20170904153504.27963-1-enric.balletbo@collabora.com>", "References": "<20170904153504.27963-1-enric.balletbo@collabora.com>", "Sender": "devicetree-owner@vger.kernel.org", "Precedence": "bulk", "List-ID": "<devicetree.vger.kernel.org>", "X-Mailing-List": "devicetree@vger.kernel.org" }, "content": "Brightness is not perceived linearly; rather, it typically follows some\nkind of parabolic curve. We can support this by skipping values in the\nbrightness-levels array in a pseudo-quadratic curve. Typically we used\nless than 256 levels, which yields no more than 1KiB of memory in our\ndevice tree. But, we've noticed that on some devices the backlight\nperforms much smoother at lower ranges if we have more than 256-levels of\ngranularity. On kevin device, for example, if we support all 64K, that\nwill waste us at least 256KiB in our device tree.\n\nLet's avoid to waste memory and have a huge table of numbers in our device\ntree of numbers by adding a brightness-levels-scale property to let the\ndriver compute the brightness levels based on one algorithm and their\nproperty parameters.\n\nSigned-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>\n---\n .../bindings/leds/backlight/pwm-backlight.txt | 21 +++++++++++++++++++++\n 1 file changed, 21 insertions(+)", "diff": "diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt\nindex 764db86..11c5583 100644\n--- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt\n+++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt\n@@ -17,6 +17,16 @@ Optional properties:\n \"pwms\" property (see PWM binding[0])\n - enable-gpios: contains a single GPIO specifier for the GPIO which enables\n and disables the backlight (see GPIO binding[1])\n+ - brightness-levels-scale: this can be used instead of 'brightness-levels',\n+ to represent the perceived luminance. So rather\n+ than specifying 'brightness-levels = <0\n+ 1 2 ... 65535>', one can simply say\n+ 'brightness-levels-scale = <255 65535>', where the\n+ first number is the max number of levels and the\n+ second number is the max PWM value that represent a\n+ 100% duty cycle (brightest). The result is a\n+ correction table for PWM values to create linear\n+ brightness based on the CIE1931 algorithm.\n \n [0]: Documentation/devicetree/bindings/pwm/pwm.txt\n [1]: Documentation/devicetree/bindings/gpio/gpio.txt\n@@ -33,3 +43,14 @@ Example:\n \t\tpower-supply = <&vdd_bl_reg>;\n \t\tenable-gpios = <&gpio 58 0>;\n \t};\n+\n+\tbacklight {\n+\t\tcompatible = \"pwm-backlight\";\n+\t\tpwms = <&pwm 0 5000000>;\n+\n+\t\tbrightness-levels-scale = <255 65535>;\n+\t\tdefault-brightness-level = <128>;\n+\n+\t\tpower-supply = <&vdd_bl_reg>;\n+\t\tenable-gpios = <&gpio 58 0>;\n+\t};\n", "prefixes": [ "RFC", "1/2" ] }