From patchwork Thu Jun 13 19:43:23 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthias Kaehlcke X-Patchwork-Id: 10993603 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id C40E914E5 for ; Thu, 13 Jun 2019 19:43:35 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id B44E322B26 for ; Thu, 13 Jun 2019 19:43:35 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id A786726256; Thu, 13 Jun 2019 19:43:35 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 41C3F22B26 for ; Thu, 13 Jun 2019 19:43:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729103AbfFMTne (ORCPT ); Thu, 13 Jun 2019 15:43:34 -0400 Received: from mail-pf1-f196.google.com ([209.85.210.196]:44899 "EHLO mail-pf1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729086AbfFMTnd (ORCPT ); Thu, 13 Jun 2019 15:43:33 -0400 Received: by mail-pf1-f196.google.com with SMTP id t16so12440390pfe.11 for ; Thu, 13 Jun 2019 12:43:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=CYPkZ1kHlegoet40jMp9lNjbYY87zm41fO5/bnIRtVY=; b=FE4dJnLkWT/wzZIKxQnGm9hn3MWtcyqW/MT2wtn2Lwp9cOyu42ILOuYP/pEZisNPzJ arWgE8Ibze4Nb38GlZev9QW5KIPYAqK71cPwZGLO95/fclJ3exbgai9UrDk+z1owjH5m oEzN4hVjAhOfbGDr0fVqTnrlE/qoPBYiECaho= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=CYPkZ1kHlegoet40jMp9lNjbYY87zm41fO5/bnIRtVY=; b=ETWt5CgeXpHyKMirhdFKa7N7lghyPiys41g7HgeZklQdUxRhSVDvU10n2E5xYd7bU1 9rl1Und5BSxsTfTY16XbTGF+xJtHeXO9z9+fWZPNJw3bqZvGkX4kMchUZ400DOnE7CCF YLwmmN2PODsCY5xLQDNzqOIC9JgqIle5bZxyA2pAOKMClnHRKe4D3A8GDogJkbDQ/IXp qs6TD/XFdQGv76bWEQaEdcZiPS79z1QgSVJR+xf5KHLVUWjDMJOINQvowUOqX7lZYsVA ajRtXQLRT/knn5g8CTZZNeBFCQk6wCazaSgtEsbcm70atfd/+2+vOb0lvYasLHuzbT6x pRKQ== X-Gm-Message-State: APjAAAXxiTQX7r0hTgYxjxM/2NkC4W5kcPVwj6FdKQomAshnaXeDQdI9 tnUmEI+PfOX+l/iFoWSH4g/KGQ== X-Google-Smtp-Source: APXvYqycbVZXlvuqRzFiBln7zYVKC7ylbynb1qlibWK1KEuqMaOj0glQOfDd2xEXmxZcdeBGNd5Pvw== X-Received: by 2002:a63:4c:: with SMTP id 73mr30610167pga.134.1560455012940; Thu, 13 Jun 2019 12:43:32 -0700 (PDT) Received: from localhost ([2620:15c:202:1:75a:3f6e:21d:9374]) by smtp.gmail.com with ESMTPSA id v23sm7853735pju.3.2019.06.13.12.43.32 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 13 Jun 2019 12:43:32 -0700 (PDT) From: Matthias Kaehlcke To: Thierry Reding , Lee Jones , Daniel Thompson , Jingoo Han , Bartlomiej Zolnierkiewicz Cc: linux-pwm@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, Enric Balletbo i Serra , Douglas Anderson , Brian Norris , Pavel Machek , Jacek Anaszewski , Matthias Kaehlcke Subject: [PATCH 1/4] MAINTAINERS: Add entry for stable backlight sysfs ABI documentation Date: Thu, 13 Jun 2019 12:43:23 -0700 Message-Id: <20190613194326.180889-2-mka@chromium.org> X-Mailer: git-send-email 2.22.0.rc2.383.gf4fbbf30c2-goog In-Reply-To: <20190613194326.180889-1-mka@chromium.org> References: <20190613194326.180889-1-mka@chromium.org> MIME-Version: 1.0 Sender: linux-fbdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Add an entry for the stable backlight sysfs ABI to the MAINTAINERS file. Signed-off-by: Matthias Kaehlcke Acked-by: Daniel Thompson --- MAINTAINERS | 1 + 1 file changed, 1 insertion(+) diff --git a/MAINTAINERS b/MAINTAINERS index 57f496cff999..d51e74340870 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -2857,6 +2857,7 @@ F: drivers/video/backlight/ F: include/linux/backlight.h F: include/linux/pwm_backlight.h F: Documentation/devicetree/bindings/leds/backlight +F: Documentation/ABI/stable/sysfs-class-backlight BATMAN ADVANCED M: Marek Lindner From patchwork Thu Jun 13 19:43:24 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthias Kaehlcke X-Patchwork-Id: 10993617 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 9B31113AF for ; Thu, 13 Jun 2019 19:43:55 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 8CDDD26255 for ; Thu, 13 Jun 2019 19:43:55 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 8045822B26; Thu, 13 Jun 2019 19:43:55 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id CA5FB22B26 for ; Thu, 13 Jun 2019 19:43:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729241AbfFMTnf (ORCPT ); Thu, 13 Jun 2019 15:43:35 -0400 Received: from mail-pl1-f195.google.com ([209.85.214.195]:44361 "EHLO mail-pl1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728667AbfFMTnf (ORCPT ); Thu, 13 Jun 2019 15:43:35 -0400 Received: by mail-pl1-f195.google.com with SMTP id t7so5950393plr.11 for ; Thu, 13 Jun 2019 12:43:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=q4BSkCRfdgzlLvM5pohgZYvjZaagG1zLW3drtbk+Qhg=; b=lxwM+SO51jAiE9bLtP0XDCOQurdUo1Ri46k55Kurq5cO1fqtibTc0rZ5lJxZrw0whL uN5SdWgRC9YgPm/s8qCWDN7PdykdOfYykIHep0dcXHsDLA8UQ4OlNEgzXwgerNsxt63Q 1MW+G2SuhzxMbbhPnZCvjJuSmC5VZ2vOByU0w= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=q4BSkCRfdgzlLvM5pohgZYvjZaagG1zLW3drtbk+Qhg=; b=dKRl4Y0UzIl/umEPC0g0C2eM5BILVYB3YbfAm2aU+GKmbQI6admu8EdP0RkbMJoB4h OMaR+hvEx7fvIf1xeWdB8p4PQIAcPBkSngiQLB4GCFrMuEKaMRS9FvpqA8BXAYNXg7/Q VSHFKtd2SGb22syhKhJfbUTpdVpCuSCHVIUDFOQD9geiicvUsyNUyQgQrmTxHcixoamE 6om4UiDuoIS1bdjH9ajeKDaW275M/S0z55GeJpwz3cManZR6CrUChW3erwcVEfaWzwGp BGv56FeD+RfYs/gP2PlSHUEAX64wlpp4KV3KcJlA6uQJvYpKK48ovkBUq51R0cPhn9/1 gKOA== X-Gm-Message-State: APjAAAXuXC18jIkbC9t/JQv94pvfQI35db5pTKCfHlmvuxfu0G0DoeOI JmlzuGJyvAyWv7EMm66HjdWl/w== X-Google-Smtp-Source: APXvYqyIBpmRRwaicUy+QVhi2lcPIOQ1QOIJ9zgUwQn1Or6pv+d/OfmPcu5gUoHzrU3n85d4/66jqQ== X-Received: by 2002:a17:902:8bc3:: with SMTP id r3mr4000015plo.161.1560455014572; Thu, 13 Jun 2019 12:43:34 -0700 (PDT) Received: from localhost ([2620:15c:202:1:75a:3f6e:21d:9374]) by smtp.gmail.com with ESMTPSA id x5sm636809pjp.21.2019.06.13.12.43.33 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 13 Jun 2019 12:43:34 -0700 (PDT) From: Matthias Kaehlcke To: Thierry Reding , Lee Jones , Daniel Thompson , Jingoo Han , Bartlomiej Zolnierkiewicz Cc: linux-pwm@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, Enric Balletbo i Serra , Douglas Anderson , Brian Norris , Pavel Machek , Jacek Anaszewski , Matthias Kaehlcke Subject: [PATCH 2/4] backlight: Expose brightness curve type through sysfs Date: Thu, 13 Jun 2019 12:43:24 -0700 Message-Id: <20190613194326.180889-3-mka@chromium.org> X-Mailer: git-send-email 2.22.0.rc2.383.gf4fbbf30c2-goog In-Reply-To: <20190613194326.180889-1-mka@chromium.org> References: <20190613194326.180889-1-mka@chromium.org> MIME-Version: 1.0 Sender: linux-fbdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Backlight brightness curves can have different shapes. The two main types are linear and non-linear curves. The human eye doesn't perceive linearly increasing/decreasing brightness as linear (see also 88ba95bedb79 "backlight: pwm_bl: Compute brightness of LED linearly to human eye"), hence many backlights use non-linear (often logarithmic) brightness curves. The type of curve currently is opaque to userspace, so userspace often relies on more or less reliable heuristics (like the number of brightness levels) to decide whether to treat a backlight device as linear or non-linear. Export the type of the brightness curve via the new sysfs attribute 'scale'. The value of the attribute may be a simple string like 'linear' or 'non-linear', or a composite string similar to 'compatible' strings of the device tree. A composite string consists of different elements separated by commas, starting with the most-detailed description and ending with the least-detailed one. An example for a composite string is "cie-1931,perceptual,non-linear" This brightness curve was generated with the CIE 1931 algorithm, it is perceptually linear, but not actually linear in terms of the emitted light. If userspace doesn't know about 'cie-1931' or 'perceptual' it should at least be able to interpret the 'non-linear' part. For devices that don't provide information about the scale of their brightness curve the value of the 'scale' attribute is 'unknown'. Signed-off-by: Matthias Kaehlcke --- .../ABI/testing/sysfs-class-backlight | 32 +++++++++++++++++++ MAINTAINERS | 1 + drivers/video/backlight/backlight.c | 22 +++++++++++++ include/linux/backlight.h | 10 ++++++ 4 files changed, 65 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-class-backlight diff --git a/Documentation/ABI/testing/sysfs-class-backlight b/Documentation/ABI/testing/sysfs-class-backlight new file mode 100644 index 000000000000..924fb68940e6 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-class-backlight @@ -0,0 +1,32 @@ +What: /sys/class/backlight//scale +Date: June 2019 +KernelVersion: 5.4 +Contact: Daniel Thompson +Description: + Description of the scale of the brightness curve. The + description consists of one or more elements separated by + commas, from the most detailed to the least detailed + description. + + Possible values are: + + unknown + The scale of the brightness curve is unknown. + + linear + The brightness changes linearly in terms of the emitted + light, changes are perceived as non-linear by the human eye. + + non-linear + The brightness changes non-linearly in terms of the emitted + light, changes might be perceived as linear by the human eye. + + perceptual,non-linear + The brightness changes non-linearly in terms of the emitted + light, changes should be perceived as linear by the human eye. + + cie-1931,perceptual,non-linear + The brightness curves was calculated with the CIE 1931 + algorithm. Brightness changes non-linearly in terms of the + emitted light, changes should be perceived as linear by the + human eye. diff --git a/MAINTAINERS b/MAINTAINERS index d51e74340870..c46812510ba5 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -2858,6 +2858,7 @@ F: include/linux/backlight.h F: include/linux/pwm_backlight.h F: Documentation/devicetree/bindings/leds/backlight F: Documentation/ABI/stable/sysfs-class-backlight +F: Documentation/ABI/testing/sysfs-class-backlight BATMAN ADVANCED M: Marek Lindner diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c index 1ef8b6fd62ac..c6e6ea6f2688 100644 --- a/drivers/video/backlight/backlight.c +++ b/drivers/video/backlight/backlight.c @@ -32,6 +32,15 @@ static const char *const backlight_types[] = { [BACKLIGHT_FIRMWARE] = "firmware", }; +static const char *const backlight_scale_types[] = { + [BACKLIGHT_SCALE_UNKNOWN] = "unknown", + [BACKLIGHT_SCALE_CIE1931] = "cie-1931,perceptual,non-linear", + [BACKLIGHT_SCALE_PERCEPTUAL] = "perceptual,non-linear", + [BACKLIGHT_SCALE_LINEAR] = "linear", + [BACKLIGHT_SCALE_NON_LINEAR] = "non-linear", +}; + + #if defined(CONFIG_FB) || (defined(CONFIG_FB_MODULE) && \ defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE)) /* This callback gets called when something important happens inside a @@ -246,6 +255,18 @@ static ssize_t actual_brightness_show(struct device *dev, } static DEVICE_ATTR_RO(actual_brightness); +static ssize_t scale_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + struct backlight_device *bd = to_backlight_device(dev); + + if (WARN_ON(bd->props.scale > BACKLIGHT_SCALE_NON_LINEAR)) + return sprintf(buf, "unknown\n"); + + return sprintf(buf, "%s\n", backlight_scale_types[bd->props.scale]); +} +static DEVICE_ATTR_RO(scale); + static struct class *backlight_class; #ifdef CONFIG_PM_SLEEP @@ -292,6 +313,7 @@ static struct attribute *bl_device_attrs[] = { &dev_attr_brightness.attr, &dev_attr_actual_brightness.attr, &dev_attr_max_brightness.attr, + &dev_attr_scale.attr, &dev_attr_type.attr, NULL, }; diff --git a/include/linux/backlight.h b/include/linux/backlight.h index 0b5897446dca..62e4ab162f34 100644 --- a/include/linux/backlight.h +++ b/include/linux/backlight.h @@ -46,6 +46,14 @@ enum backlight_notification { BACKLIGHT_UNREGISTERED, }; +enum backlight_scale { + BACKLIGHT_SCALE_UNKNOWN, + BACKLIGHT_SCALE_CIE1931 = 1, + BACKLIGHT_SCALE_PERCEPTUAL, + BACKLIGHT_SCALE_LINEAR, + BACKLIGHT_SCALE_NON_LINEAR, /* needed for backwards compatibility */ +}; + struct backlight_device; struct fb_info; @@ -80,6 +88,8 @@ struct backlight_properties { enum backlight_type type; /* Flags used to signal drivers of state changes */ unsigned int state; + /* Type of the brightness scale (linear, non-linear, ...) */ + enum backlight_scale scale; #define BL_CORE_SUSPENDED (1 << 0) /* backlight is suspended */ #define BL_CORE_FBBLANK (1 << 1) /* backlight is under an fb blank event */ From patchwork Thu Jun 13 19:43:25 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthias Kaehlcke X-Patchwork-Id: 10993615 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id C2B0D14E5 for ; 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Thu, 13 Jun 2019 12:43:36 -0700 (PDT) Received: from localhost ([2620:15c:202:1:75a:3f6e:21d:9374]) by smtp.gmail.com with ESMTPSA id b17sm525029pfb.18.2019.06.13.12.43.35 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 13 Jun 2019 12:43:35 -0700 (PDT) From: Matthias Kaehlcke To: Thierry Reding , Lee Jones , Daniel Thompson , Jingoo Han , Bartlomiej Zolnierkiewicz Cc: linux-pwm@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, Enric Balletbo i Serra , Douglas Anderson , Brian Norris , Pavel Machek , Jacek Anaszewski , Matthias Kaehlcke Subject: [PATCH 3/4] backlight: pwm_bl: Set scale type for CIE 1931 curves Date: Thu, 13 Jun 2019 12:43:25 -0700 Message-Id: <20190613194326.180889-4-mka@chromium.org> X-Mailer: git-send-email 2.22.0.rc2.383.gf4fbbf30c2-goog In-Reply-To: <20190613194326.180889-1-mka@chromium.org> References: <20190613194326.180889-1-mka@chromium.org> MIME-Version: 1.0 Sender: linux-fbdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP For backlight curves calculated with the CIE 1931 algorithm set the brightness scale type property accordingly. This makes the scale type available to userspace via the 'scale' sysfs attribute. Signed-off-by: Matthias Kaehlcke Tested-by: Enric Balletbo i Serra Acked-by: Daniel Thompson --- drivers/video/backlight/pwm_bl.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index fb45f866b923..f067fe7aa35d 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -553,6 +553,8 @@ static int pwm_backlight_probe(struct platform_device *pdev) goto err_alloc; } + memset(&props, 0, sizeof(struct backlight_properties)); + if (data->levels) { /* * For the DT case, only when brightness levels is defined @@ -591,6 +593,8 @@ static int pwm_backlight_probe(struct platform_device *pdev) pb->levels = data->levels; } + + props.scale = BACKLIGHT_SCALE_CIE1931; } else { /* * That only happens for the non-DT case, where platform data @@ -601,7 +605,6 @@ static int pwm_backlight_probe(struct platform_device *pdev) pb->lth_brightness = data->lth_brightness * (state.period / pb->scale); - memset(&props, 0, sizeof(struct backlight_properties)); props.type = BACKLIGHT_RAW; props.max_brightness = data->max_brightness; bl = backlight_device_register(dev_name(&pdev->dev), &pdev->dev, pb, From patchwork Thu Jun 13 19:43:26 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthias Kaehlcke X-Patchwork-Id: 10993611 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 0D52F14E5 for ; Thu, 13 Jun 2019 19:43:44 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id F372822B26 for ; Thu, 13 Jun 2019 19:43:43 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id E6F1326256; Thu, 13 Jun 2019 19:43:43 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 9015222B26 for ; 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This makes the scale type available to userspace via the 'scale' sysfs attribute. To determine if a curve is linear it is compared to a interpolated linear curve between min and max brightness. The curve is considered linear if no value deviates more than +/-5% of ${brightness_range} from their interpolated value. Signed-off-by: Matthias Kaehlcke Acked-by: Daniel Thompson --- drivers/video/backlight/pwm_bl.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index f067fe7aa35d..912407b6d67f 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -404,6 +404,26 @@ int pwm_backlight_brightness_default(struct device *dev, } #endif +static bool pwm_backlight_is_linear(struct platform_pwm_backlight_data *data) +{ + unsigned int nlevels = data->max_brightness + 1; + unsigned int min_val = data->levels[0]; + unsigned int max_val = data->levels[nlevels - 1]; + unsigned int slope = (100 * (max_val - min_val)) / nlevels; + unsigned int margin = (max_val - min_val) / 20; /* 5% */ + int i; + + for (i = 1; i < nlevels; i++) { + unsigned int linear_value = min_val + ((i * slope) / 100); + unsigned int delta = abs(linear_value - data->levels[i]); + + if (delta > margin) + return false; + } + + return true; +} + static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb) { struct device_node *node = pb->dev->of_node; @@ -567,6 +587,11 @@ static int pwm_backlight_probe(struct platform_device *pdev) pb->levels = data->levels; } + + if (pwm_backlight_is_linear(data)) + props.scale = BACKLIGHT_SCALE_LINEAR; + else + props.scale = BACKLIGHT_SCALE_NON_LINEAR; } else if (!data->max_brightness) { /* * If no brightness levels are provided and max_brightness is