From patchwork Thu Sep 19 14:06:16 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Rasmus Villemoes X-Patchwork-Id: 11152537 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 868C976 for ; Thu, 19 Sep 2019 14:06:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 645D32067B for ; Thu, 19 Sep 2019 14:06:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=rasmusvillemoes.dk header.i=@rasmusvillemoes.dk header.b="OCn3gIYj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388712AbfISOGb (ORCPT ); Thu, 19 Sep 2019 10:06:31 -0400 Received: from mail-lf1-f68.google.com ([209.85.167.68]:45592 "EHLO mail-lf1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388639AbfISOGa (ORCPT ); Thu, 19 Sep 2019 10:06:30 -0400 Received: by mail-lf1-f68.google.com with SMTP id r134so2438134lff.12 for ; Thu, 19 Sep 2019 07:06:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rasmusvillemoes.dk; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=9jGZhci6ir2QQxaMaZ4RPKwsW6VmlML93zQ3UVVvLVc=; b=OCn3gIYj+wUYxAtXas8eOyf4fSEWhP2JZywuNcvWhoXd2re/NpOYXHVgx+ktYyP5cV f+T9+6Yleq+jPzmdljsDSTYYkv0hRJ4OXI6VngwNHBQhZ+MPKG8XvWun3Tnm4NO4agx6 jyhuQWbNOO26WlFgyizU4iA2+osQUAPnhKYiE= 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:mime-version :content-transfer-encoding; bh=9jGZhci6ir2QQxaMaZ4RPKwsW6VmlML93zQ3UVVvLVc=; b=ui4BOAHc2L+ZkjW/L2XULpu9pAt05HFML9EBbH3Qix/akYEKS7B17Sex7UGNjVGm88 OO74OOnAjzv+4VqQzMOf2YezpnoBMs0a15fNABYF+WdDgUfZSMdDR7l/PAC1RLV9xsEO NCj07WwlZs+nsj2yGRWX+yCQM5OiyrPi3zF5rt9MszQncSEhHsFyl20j6G2MJbwwCmFE yF+U70xwLGXNyct11HAvrSJPgV4sUhkwPMTGMqWxkXq+2aYVGn3WOMWT9Xi2sxDhVo/+ OQ3n747TrzNkzXUPQaO8VAFVrQ1+uggZYnRD0My9ZoWKbOMHClO9CMdIyrOD+/qpjlG1 uYow== X-Gm-Message-State: APjAAAUD+lqutWwQE2eQS/9YNmeBPDF6zTmj5j1vidFH3RxqTJIFqVeO KL94EO7yx6cubexWkZ/kbrdu9w== X-Google-Smtp-Source: APXvYqx94tejJIy0k7sD7BxbdRz2nLUSrH5aFo9cmoMdLo9lK0ILNVQtax9BnK0daUvVanbqCyRpiw== X-Received: by 2002:ac2:51a7:: with SMTP id f7mr5064133lfk.119.1568901989001; Thu, 19 Sep 2019 07:06:29 -0700 (PDT) Received: from prevas-ravi.prevas.se ([81.216.59.226]) by smtp.gmail.com with ESMTPSA id h3sm1687886ljf.12.2019.09.19.07.06.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Sep 2019 07:06:28 -0700 (PDT) From: Rasmus Villemoes To: Thierry Reding , Lee Jones , Daniel Thompson , Jingoo Han , Bartlomiej Zolnierkiewicz Cc: Rasmus Villemoes , linux-pwm@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/5] backlight: pwm_bl: fix cie1913 comments and constant Date: Thu, 19 Sep 2019 16:06:16 +0200 Message-Id: <20190919140620.32407-1-linux@rasmusvillemoes.dk> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Sender: linux-fbdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org The "break-even" point for the two formulas is L==8, which is also what the code actually implements. [Incidentally, at that point one has Y=0.008856, not 0.08856]. Moreover, all the sources I can find say the linear factor is 903.3 rather than 902.3, which makes sense since then the formulas agree at L==8, both yielding the 0.008856 figure to four significant digits. Signed-off-by: Rasmus Villemoes Reviewed-by: Daniel Thompson --- drivers/video/backlight/pwm_bl.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index 2201b8c78641..be36be1cacb7 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -155,8 +155,8 @@ static const struct backlight_ops pwm_backlight_ops = { * * The CIE 1931 lightness formula is what actually describes how we perceive * light: - * Y = (L* / 902.3) if L* ≤ 0.08856 - * Y = ((L* + 16) / 116)^3 if L* > 0.08856 + * Y = (L* / 903.3) if L* ≤ 8 + * Y = ((L* + 16) / 116)^3 if L* > 8 * * Where Y is the luminance, the amount of light coming out of the screen, and * is a number between 0.0 and 1.0; and L* is the lightness, how bright a human @@ -169,9 +169,15 @@ static u64 cie1931(unsigned int lightness, unsigned int scale) { u64 retval; + /* + * @lightness is given as a number between 0 and 1, expressed + * as a fixed-point number in scale @scale. Convert to a + * percentage, still expressed as a fixed-point number, so the + * above formulas can be applied. + */ lightness *= 100; if (lightness <= (8 * scale)) { - retval = DIV_ROUND_CLOSEST_ULL(lightness * 10, 9023); + retval = DIV_ROUND_CLOSEST_ULL(lightness * 10, 9033); } else { retval = int_pow((lightness + (16 * scale)) / 116, 3); retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale));