From patchwork Tue Jul 9 19:00:07 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthias Kaehlcke X-Patchwork-Id: 11037413 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 05AAF912 for ; Tue, 9 Jul 2019 19:00:26 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id EB6412870D for ; Tue, 9 Jul 2019 19:00:25 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id DFD9C2872F; Tue, 9 Jul 2019 19:00:25 +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 808A12870D for ; Tue, 9 Jul 2019 19:00:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727763AbfGITAY (ORCPT ); Tue, 9 Jul 2019 15:00:24 -0400 Received: from mail-pl1-f195.google.com ([209.85.214.195]:43108 "EHLO mail-pl1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729004AbfGITAT (ORCPT ); Tue, 9 Jul 2019 15:00:19 -0400 Received: by mail-pl1-f195.google.com with SMTP id cl9so10533381plb.10 for ; Tue, 09 Jul 2019 12:00:19 -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=7VTnoQhILwKHLps+gGfkisxkuSKBxEyo68mEBQUHAaY=; b=kfV/7/kvbkaJ7UsIzdsFDRlAMdzpK6L6mf+hCSJgo/ppqnLdG493pA1TwsgBo8gqI+ 4m8IhLpUYafypQV62VutcuQ/xBvf5+Qfw9xSrUk4r15c6IIY+l2X2T26Z72GsIoqOOBe J11qlTxGksNKv6aSrfL+fr+Nca1CmutGbOxRA= 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=7VTnoQhILwKHLps+gGfkisxkuSKBxEyo68mEBQUHAaY=; b=gcuuXprw5w1u5IvCRscZStmmKrdsYlfVfAYyYlPn3h5StBG5RxhSAzBDLMeJoJS6zX Jiu0HLgKJ7kyL1gx+OwY/O5pEzqtmHWqiCmaoWmC4voXK6b/S9adFmg8AzpctBv1APaP 7WSJEUXxr6k+p64aQcuFquKq97FzjxAfwwVXG6b/gfPTQ7DBgIX6b+VWT5bJTQ+cjQ97 KnAUljttJTYC0tnaM4KHHWT3ww1sp+o9hefTMhzZ/rPvFfWyvZXpxKnilHKPnhRX6ry+ 3VLPxUJScYmousxgPJ8qxUuDRwJV2qa64EkDyWZ8V6ExLCeuI5Z62IYGA8k2duTdcBqu +9Xg== X-Gm-Message-State: APjAAAW2oMVnGQtXA1ObbRU8jUyOUG01Ik1FBDsrOCcVBAoZ3ugbVtms osXNY68OXhFTC4BJtsT/RyXqNQ== X-Google-Smtp-Source: APXvYqyFxcn+t9rWGoWrMrwk7IGCCiVhSunnF0u4fJQLec9Z7/8us2QIzzEsGo2V3Ixk/lZr9QooRQ== X-Received: by 2002:a17:902:29e6:: with SMTP id h93mr32447140plb.297.1562698818959; Tue, 09 Jul 2019 12:00:18 -0700 (PDT) Received: from localhost ([2620:15c:202:1:75a:3f6e:21d:9374]) by smtp.gmail.com with ESMTPSA id v63sm8391683pfv.174.2019.07.09.12.00.18 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 09 Jul 2019 12:00:18 -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 v3 4/4] backlight: pwm_bl: Set scale type for brightness curves specified in the DT Date: Tue, 9 Jul 2019 12:00:07 -0700 Message-Id: <20190709190007.91260-5-mka@chromium.org> X-Mailer: git-send-email 2.22.0.410.gd8fdbe21b5-goog In-Reply-To: <20190709190007.91260-1-mka@chromium.org> References: <20190709190007.91260-1-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 Check if a brightness curve specified in the device tree is linear or not and set the corresponding property accordingly. 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 --- Changes in v3: - none Changes in v2: - use 128 (power of two) instead of 100 as factor for the slope - add comment about max quantization error - added Daniel's 'Acked-by' tag --- drivers/video/backlight/pwm_bl.c | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index 7c6dfc4a601d..fef98beb8b7e 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -404,6 +404,31 @@ 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]; + /* + * Multiplying by 128 means that even in pathological cases such + * as (max_val - min_val) == nlevels the error at max_val is less + * than 1%. + */ + unsigned int slope = (128 * (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) / 128); + 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 +592,11 @@ 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