From patchwork Tue Oct 8 12:03:24 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Rasmus Villemoes X-Patchwork-Id: 11179483 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 EA9C0112B for ; Tue, 8 Oct 2019 12:05:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CCA5C21835 for ; Tue, 8 Oct 2019 12:05:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=rasmusvillemoes.dk header.i=@rasmusvillemoes.dk header.b="W0ddgUpZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730893AbfJHMFV (ORCPT ); Tue, 8 Oct 2019 08:05:21 -0400 Received: from mail-lj1-f196.google.com ([209.85.208.196]:32894 "EHLO mail-lj1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730890AbfJHMFV (ORCPT ); Tue, 8 Oct 2019 08:05:21 -0400 Received: by mail-lj1-f196.google.com with SMTP id a22so17248809ljd.0 for ; Tue, 08 Oct 2019 05:05:19 -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:in-reply-to:references :mime-version:content-transfer-encoding; bh=kZ+v3Ie5jsyMpg1/r8HbbsX7sXk3b8d5gKwzOHbV1b8=; b=W0ddgUpZ8caX090N18rJXEGsy5RctbdFr4Uj8eEHV+WXpAquDOJGemg+ouB0b7rO2k wQfnFphLbbQKFY/9KqpuIJl8qs1h1g3Lae36ILXsc4WNO/eomzP41sRPtH5RcLggU2XK ai8CJyNSJdiOh5PVAUkZIqTEPEq2lsZk8iZhY= 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=kZ+v3Ie5jsyMpg1/r8HbbsX7sXk3b8d5gKwzOHbV1b8=; b=BqUnjz9my4Q1OoN/DI2igIGxajT5BvpypndW984Irudyy2dLBX5vyDrYdHsJxPXXBJ H3uJz0R9RyRPcZTZNEOGvRemspyrU0GAIdkBz7t5jhxtfTslvbFM6nLk7WdFMCsdCavl dDMHb27we85GRX047FeiJBy5xshEToUD9k9F89kTCTSu4l6DFsWjMLKrH15iCU04WgfZ 74zCsSj8dYByPMPIHOVXpYHVDxo3YiCiNco9pd8loYn+qHG+0zE9H1jOGKOpgp/FrInO Tc6TV+MkMHopxLpY8RGxqqqOoi72bGygS3N/IUK4QaTcZ+JvVB7TEec/phPOLq6fAqKU Ag3A== X-Gm-Message-State: APjAAAWipruHB6t//9dAc33DniokmbG0nNfsyvU7YUTAh6U/VLgiXf3i Nh3CiyF0N0dYOUtoqWZM1VnaMg== X-Google-Smtp-Source: APXvYqxr3LSKZs/gnEdARVmL8Fu4FXziognliaJ/7eGB45xQLrMsXf20NWCHuBIyf534zW7ay+klcg== X-Received: by 2002:a2e:810e:: with SMTP id d14mr22480784ljg.160.1570536318667; Tue, 08 Oct 2019 05:05:18 -0700 (PDT) Received: from prevas-ravi.prevas.se ([81.216.59.226]) by smtp.gmail.com with ESMTPSA id z18sm3918033ljh.17.2019.10.08.05.05.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Oct 2019 05:05:17 -0700 (PDT) From: Rasmus Villemoes To: Thierry Reding , =?utf-8?q?Uwe_Kleine-K=C3=B6n?= =?utf-8?q?ig?= , 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 v2 1/4] backlight: pwm_bl: fix cie1913 comments and constant Date: Tue, 8 Oct 2019 14:03:24 +0200 Message-Id: <20191008120327.24208-2-linux@rasmusvillemoes.dk> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20191008120327.24208-1-linux@rasmusvillemoes.dk> References: <20191008120327.24208-1-linux@rasmusvillemoes.dk> 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. Reviewed-by: Daniel Thompson Signed-off-by: Rasmus Villemoes --- 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 746eebc411df..cc44a02e95c7 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));