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)); From patchwork Tue Oct 8 12:03:25 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Rasmus Villemoes X-Patchwork-Id: 11179477 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 A367B112B for ; Tue, 8 Oct 2019 12:05:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 84A8E206C2 for ; Tue, 8 Oct 2019 12:05:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=rasmusvillemoes.dk header.i=@rasmusvillemoes.dk header.b="ELuDRuvE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730912AbfJHMFY (ORCPT ); Tue, 8 Oct 2019 08:05:24 -0400 Received: from mail-lj1-f195.google.com ([209.85.208.195]:36200 "EHLO mail-lj1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730750AbfJHMFX (ORCPT ); Tue, 8 Oct 2019 08:05:23 -0400 Received: by mail-lj1-f195.google.com with SMTP id v24so17245442ljj.3 for ; Tue, 08 Oct 2019 05:05:22 -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=t1XvNBeL5bYKnc6NbbptU+vm2vXQBBrTO687+/k8huo=; b=ELuDRuvEPbxHn+tPF2h2RxCruUdG8zM+LbvVMlIluH8Z/3Nz3rM48QruNf6Jjzt6Qx s+T3vGwTXw/HUazqjiUT8y6NaXwohlIowNQCdfwlwMsrwKqKmMOt9HlxSOwPJeCD4YOl uaNX5F5hIsDxJs3FYKG+NK0+p/NucTLWFjocY= 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=t1XvNBeL5bYKnc6NbbptU+vm2vXQBBrTO687+/k8huo=; b=ETdXxgAmrj5xsG+Mr8hzltf12aDjhohhRP35evKoW+5Sg7NdprOdnK+g9suy37LeIS 26ET9HTjzN4ZQAohF5QYYt+7dqqGS6SMjnE3gDQWKN1XyUJ+L8vjO+1s+KOjIReKIf/N +7SJhdHTK/JqToKSQxSvzzNmqOzxFz7pv9Vs8bddKOXek+AmAelugyZDkyiss2qhO9Zq V2sU09MY9nwDiTP7MYZEL9akymSG+MmXvO11EYCHfqCobZz2JzltMWqX9bbCnlj6xTNo Ndwoti93SG7AwJEoVUHu8FEt59pImD2+TnQgWeg2r5yzsayeY9FTLphLy8mo7qEYbLi1 ZBtw== X-Gm-Message-State: APjAAAWPNYEtnHiypwJBCPIzN+Kl6PlC3qyHeaNfpUwYNZuBOi71ptJc RdBGUAUgv9QrXcglrvHa4MjSjQ== X-Google-Smtp-Source: APXvYqwr3eVj5VGcs9c4XwSP3Lzo4ODiUPJZt5VqFcpdr7xw+mtUtMYtWeZVNZS+BWY7vjjUDAVqgQ== X-Received: by 2002:a2e:9d16:: with SMTP id t22mr19624221lji.207.1570536321581; Tue, 08 Oct 2019 05:05:21 -0700 (PDT) Received: from prevas-ravi.prevas.se ([81.216.59.226]) by smtp.gmail.com with ESMTPSA id z18sm3918033ljh.17.2019.10.08.05.05.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Oct 2019 05:05:19 -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 2/4] backlight: pwm_bl: eliminate a 64/32 division Date: Tue, 8 Oct 2019 14:03:25 +0200 Message-Id: <20191008120327.24208-3-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 lightness*1000 is nowhere near overflowing 32 bits, so we can just use an ordinary 32/32 division, which is much cheaper than the 64/32 done via do_div(). Reviewed-by: Daniel Thompson Signed-off-by: Rasmus Villemoes --- drivers/video/backlight/pwm_bl.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index cc44a02e95c7..672c5e7cfcd1 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -177,7 +177,7 @@ static u64 cie1931(unsigned int lightness, unsigned int scale) */ lightness *= 100; if (lightness <= (8 * scale)) { - retval = DIV_ROUND_CLOSEST_ULL(lightness * 10, 9033); + retval = DIV_ROUND_CLOSEST(lightness * 10, 9033); } else { retval = int_pow((lightness + (16 * scale)) / 116, 3); retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale)); From patchwork Tue Oct 8 12:03:26 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Rasmus Villemoes X-Patchwork-Id: 11179479 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 C99ED1747 for ; Tue, 8 Oct 2019 12:05:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AB71B206C2 for ; Tue, 8 Oct 2019 12:05:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=rasmusvillemoes.dk header.i=@rasmusvillemoes.dk header.b="iHfqd7In" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730838AbfJHMF2 (ORCPT ); Tue, 8 Oct 2019 08:05:28 -0400 Received: from mail-lf1-f65.google.com ([209.85.167.65]:46287 "EHLO mail-lf1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730904AbfJHMF1 (ORCPT ); Tue, 8 Oct 2019 08:05:27 -0400 Received: by mail-lf1-f65.google.com with SMTP id t8so11692334lfc.13 for ; Tue, 08 Oct 2019 05:05:25 -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=GHqEF0WPzWee4xQdmsltBE/DbSJ8wdizxOO3R+g9Qfw=; b=iHfqd7InHpWSp9HtncYc/nGuUN2SQLNPz6EP4Z7c0utpCDEfBTHo79qRfdGdqnHjDc mUERS8N/Ezm1xJivvlU2FPSjziBCWfbM0Mp19xZKJ+DciElb5UKCU0Vr/UJTOEN7Raiq 9nMDdC6cEjkuK79xMF6I9qmtVilDUGJ2/wvCs= 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=GHqEF0WPzWee4xQdmsltBE/DbSJ8wdizxOO3R+g9Qfw=; b=IwFNfcf2/CbCfnC7wCj0m4I1Kavps+JO9d/2jVk3Ru0klCBuyCu0aNAmL29x4YgBcz EDKkcc9mlyq4z/ivitwXB1y5KjR0Pw0xj7JyD5CMAtk3AQWKb4xDfzv7RSxPXux1dFAS TBZ7HEKd3DPZCnw5mGAQsrYWVJARcFTdd9aR3oNL5KJaEPVUhAK50ZFbcAYGA8l4sc65 CkzWaLipT4rD6Owom6WXomdIpnHwCu2wOgVBAKuohyxsbwP6sVHttnJWkVnAjy36XoJ4 u666A70veFXdgTVJiyF5T5SEUaROj32Zr+0gAjykYk3SwZXCSj2K2ZLeYOeHWGzYYFgy V4gw== X-Gm-Message-State: APjAAAVfYYa+Y3GpIuKxPDQ6vm/4ujswQUp0IHn3e4qLDEBYydaYSZyj b8vog3khthixDvhzaIt2OyjJ2g== X-Google-Smtp-Source: APXvYqxCIRhO8rpvb/4039KpvxZ2HkirRtcoXz27yozPDPIZ8udJLy4ukMGlXb9inSVE+1v8hleq+g== X-Received: by 2002:a19:90:: with SMTP id 138mr19176383lfa.111.1570536324544; Tue, 08 Oct 2019 05:05:24 -0700 (PDT) Received: from prevas-ravi.prevas.se ([81.216.59.226]) by smtp.gmail.com with ESMTPSA id z18sm3918033ljh.17.2019.10.08.05.05.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Oct 2019 05:05:22 -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 3/4] backlight: pwm_bl: drop use of int_pow() Date: Tue, 8 Oct 2019 14:03:26 +0200 Message-Id: <20191008120327.24208-4-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 For a fixed small exponent of 3, it is more efficient to simply use two explicit multiplications rather than calling the int_pow() library function: Aside from the function call overhead, its implementation using repeated squaring means it ends up doing four 64x64 multiplications. Reviewed-by: Daniel Thompson Signed-off-by: Rasmus Villemoes --- drivers/video/backlight/pwm_bl.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index 672c5e7cfcd1..273d3fb628a0 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -179,7 +179,8 @@ static u64 cie1931(unsigned int lightness, unsigned int scale) if (lightness <= (8 * scale)) { retval = DIV_ROUND_CLOSEST(lightness * 10, 9033); } else { - retval = int_pow((lightness + (16 * scale)) / 116, 3); + retval = (lightness + (16 * scale)) / 116; + retval *= retval * retval; retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale)); } From patchwork Tue Oct 8 12:03:27 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Rasmus Villemoes X-Patchwork-Id: 11179481 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 149BD112B for ; Tue, 8 Oct 2019 12:05:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EA4C9206C2 for ; Tue, 8 Oct 2019 12:05:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=rasmusvillemoes.dk header.i=@rasmusvillemoes.dk header.b="EQxxLJPu" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730946AbfJHMFa (ORCPT ); Tue, 8 Oct 2019 08:05:30 -0400 Received: from mail-lj1-f195.google.com ([209.85.208.195]:41153 "EHLO mail-lj1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730926AbfJHMF3 (ORCPT ); Tue, 8 Oct 2019 08:05:29 -0400 Received: by mail-lj1-f195.google.com with SMTP id f5so17230332ljg.8 for ; Tue, 08 Oct 2019 05:05:28 -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=TptQKMAgu40zPvzhQ1Z31J/pJlahQ9zU95/IQSGlotQ=; b=EQxxLJPuv5kKROn32XBozgwjwLwg89RorArcZU/g8cItI4zFmL7g+GBxM/Ahg/onYr /Qq6eZw1P0LGp4IiWbUpBRj0wt8o58C+ixmMvDPdQyY9ckNxJ8fwVC+8j5r3oWi+ocMe bAPIcSJt4aI9G1QMFztBqZWK5BjdSrlZzfkn0= 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=TptQKMAgu40zPvzhQ1Z31J/pJlahQ9zU95/IQSGlotQ=; b=YypwsKUguC8til46lz9AZDEmaLvpePLNl3PxsGv8KX7q1N4uJ+WZMTT01N5LwUaYxJ hUDZcjQ6sCeY/BSvHn8fvKx9ECKHw1rIA7kb1ZXX+yBce6ZnH2Y2RHpj4ypuLkyiCWhV fJjkn0+5yqTBBlEnKKwiH5sKVfukvcGepxaRBvIO/FB++ZKLWE4PBBwfp3KcWh5ItgJT kei36qjRN8z8Ml3hLWZeKEwlyWpbm3IYETKycpyMPi6SA3hVfFdblTcNYMkujPtiS+cE 8jNozlUzJls/2ujtOBKPIs2X3fi2bL6ltdLpXjLLctfDEzrvVDPYFWW6aKe1/Ulehiki isrQ== X-Gm-Message-State: APjAAAXsBjE983MRhFwa0n+gD0alMUYBtFTB41E9k28ehVWIP74O3ZqW iXUDR0gxCjvigfZ3nOfB0npOvA== X-Google-Smtp-Source: APXvYqz1ZVV6abC07XSZS+ewKWoIdZcZT75MUkfMcioX26MZiIhkt3Y7dE8w+s+hfv7TsUNPdK5xaw== X-Received: by 2002:a2e:b045:: with SMTP id d5mr22159030ljl.105.1570536327398; Tue, 08 Oct 2019 05:05:27 -0700 (PDT) Received: from prevas-ravi.prevas.se ([81.216.59.226]) by smtp.gmail.com with ESMTPSA id z18sm3918033ljh.17.2019.10.08.05.05.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Oct 2019 05:05:25 -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 4/4] backlight: pwm_bl: switch to power-of-2 base for fixed-point math Date: Tue, 8 Oct 2019 14:03:27 +0200 Message-Id: <20191008120327.24208-5-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 Using a power-of-2 instead of power-of-10 base makes the computations much cheaper. 2^16 is safe; retval never becomes more than 2^48 + 2^32/2. On a 32 bit platform, the very expensive 64/32 division at the end of cie1931() instead becomes essentially free (a shift by 32 is just a register rename). Reviewed-by: Daniel Thompson Signed-off-by: Rasmus Villemoes --- drivers/video/backlight/pwm_bl.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-) diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index 273d3fb628a0..a99c2210c935 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -148,7 +148,8 @@ static const struct backlight_ops pwm_backlight_ops = { }; #ifdef CONFIG_OF -#define PWM_LUMINANCE_SCALE 10000 /* luminance scale */ +#define PWM_LUMINANCE_SHIFT 16 +#define PWM_LUMINANCE_SCALE (1 << PWM_LUMINANCE_SHIFT) /* luminance scale */ /* * CIE lightness to PWM conversion. @@ -165,23 +166,25 @@ static const struct backlight_ops pwm_backlight_ops = { * The following function does the fixed point maths needed to implement the * above formula. */ -static u64 cie1931(unsigned int lightness, unsigned int scale) +static u64 cie1931(unsigned int lightness) { 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. + * as a fixed-point number in scale + * PWM_LUMINANCE_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)) { + if (lightness <= (8 * PWM_LUMINANCE_SCALE)) { retval = DIV_ROUND_CLOSEST(lightness * 10, 9033); } else { - retval = (lightness + (16 * scale)) / 116; + retval = (lightness + (16 * PWM_LUMINANCE_SCALE)) / 116; retval *= retval * retval; - retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale)); + retval += 1ULL << (2*PWM_LUMINANCE_SHIFT - 1); + retval >>= 2*PWM_LUMINANCE_SHIFT; } return retval; @@ -215,8 +218,7 @@ int pwm_backlight_brightness_default(struct device *dev, /* Fill the table using the cie1931 algorithm */ for (i = 0; i < data->max_brightness; i++) { retval = cie1931((i * PWM_LUMINANCE_SCALE) / - data->max_brightness, PWM_LUMINANCE_SCALE) * - period; + data->max_brightness) * period; retval = DIV_ROUND_CLOSEST_ULL(retval, PWM_LUMINANCE_SCALE); if (retval > UINT_MAX) return -EINVAL;