From patchwork Mon Jun 24 20:31:13 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthias Kaehlcke X-Patchwork-Id: 11014079 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 2964814E5 for ; Mon, 24 Jun 2019 20:31:31 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1A48520499 for ; Mon, 24 Jun 2019 20:31:31 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 0EB4F28BBE; Mon, 24 Jun 2019 20:31:31 +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 75BD228B90 for ; Mon, 24 Jun 2019 20:31:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731863AbfFXUba (ORCPT ); Mon, 24 Jun 2019 16:31:30 -0400 Received: from mail-pl1-f193.google.com ([209.85.214.193]:40876 "EHLO mail-pl1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731830AbfFXUb0 (ORCPT ); Mon, 24 Jun 2019 16:31:26 -0400 Received: by mail-pl1-f193.google.com with SMTP id a93so7553489pla.7 for ; Mon, 24 Jun 2019 13:31:26 -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=uZKHvCx8L/nRTrUb/ohywx0d3IXX3vcHyiOoGdIF2Vg=; b=G/bUhQslRBb9yDeN/Ju1v2H78Jn3pcV6lvi6ZsyGVCuBbzJ+oIhAcvU04QfS10U/4R pdE3J6hWbwxyP4QcHwwtH00UNcd1LgYEz2XOvY5wmOr4tiTSrA/9uD0OATvj9bqrmoPn id+vaY8rgFoQ9n7vUdhFL4XPoNNii/WHKNs9A= 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=uZKHvCx8L/nRTrUb/ohywx0d3IXX3vcHyiOoGdIF2Vg=; b=kui2FxEmyDLf3NYb2C9Lc5q7rYfVn4f5JfCxJ/5RpJQksL2hyP1soamyyM+reql33I zWxOzt0l1waRG0xf8BoFEbmIYo2hxYaDDnxWxz25WCbd46ZBHCSz/MdufvaAQCZ2aFSG amIplvU4FgfX8/v+62h541EXu0mitbhJeb2gbvtjPPz22LlYPYmU8FiGTcgWoZHAM3NS qWcVMzEjaNevNTSBjllGJ8QUzRscwiubQoLg/lxFEA3jamCwdKkXdtxM2GHLfzp5OgMm MRZ6/qAvZU9PDgba0ff/eE+rOLERVVR7MrRbq2HOrvJxcEw0hMxkwGZPc4dMzcvmifjJ e5cg== X-Gm-Message-State: APjAAAV5mkYcFshliTfXDHrrgf0dJ2OLIeG6wZzE1fGVYsCLqwBTs1oH ghZEyY12GLPvtobBtsGC5nrnhw== X-Google-Smtp-Source: APXvYqzY0+srP89wCVDbPca+cx8EHxAJHQuHwUe5lX3IaE2YnttbyJ+9Ii8mxU7OnlFea1FBJZ1y0Q== X-Received: by 2002:a17:902:2006:: with SMTP id n6mr94261265pla.232.1561408286127; Mon, 24 Jun 2019 13:31:26 -0700 (PDT) Received: from localhost ([2620:15c:202:1:75a:3f6e:21d:9374]) by smtp.gmail.com with ESMTPSA id r2sm21887470pfl.67.2019.06.24.13.31.25 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 24 Jun 2019 13:31:25 -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 v2 4/4] backlight: pwm_bl: Set scale type for brightness curves specified in the DT Date: Mon, 24 Jun 2019 13:31:13 -0700 Message-Id: <20190624203114.93277-5-mka@chromium.org> X-Mailer: git-send-email 2.22.0.410.gd8fdbe21b5-goog In-Reply-To: <20190624203114.93277-1-mka@chromium.org> References: <20190624203114.93277-1-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 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 f067fe7aa35d..2297fb4af49d 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