From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 84D14C31E45 for ; Thu, 13 Jun 2019 21:56:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2E5F621473 for ; Thu, 13 Jun 2019 21:56:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="bmGw/SSM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728396AbfFMV4v (ORCPT ); Thu, 13 Jun 2019 17:56:51 -0400 Received: from mail-pg1-f193.google.com ([209.85.215.193]:41886 "EHLO mail-pg1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726900AbfFMV4u (ORCPT ); Thu, 13 Jun 2019 17:56:50 -0400 Received: by mail-pg1-f193.google.com with SMTP id 83so260273pgg.8 for ; Thu, 13 Jun 2019 14:56:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=CqSKUfplOln9iJ64al9vHogCwxzrRaa83C6tRk2QQv4=; b=bmGw/SSMPtz8TE4EKqoCf4eLamt3dGCnE78OhZFLR1j3AZMAPdFK6N1D2wU0jpgmTc TQMHeLtGxZalAqLGnm4EwKQ86Br67IcUCO4J2VujjS2raHFk08WiqngAoT1IhPARrEaQ 02N2tSwU3jtn+gGyNBs3XOqsFEvuYN/QORCeI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=CqSKUfplOln9iJ64al9vHogCwxzrRaa83C6tRk2QQv4=; b=XP8MoXFn1Nc7LO3GZCOTlkV6czQIdp0gL97w8f7809RJx4NdSOOScUemIykIvnTi/u 35H5tngB4G8FSWnxXpJm98UjMHtMPr0N1k0d4Cs/2LGP8P0cvfza6r006k3KICGOYdA1 QsI1v40rCzmhTMluV3piLDmQ0c6e8dheM5iA7qXh06U9vGlz09H+7jpllvFkcQtBuNP+ xi0K8hsJ5qSTLq5zFMszAj+164V2oD5Tq5vpD0KnQKnqPVEoB/fy6ESJZrl9UIZGz3rb ujJeX2lJR1/f1vy2ZagAqkqqqO9EnjLTFk7wzSjyzbAADc5Qi3G9gPUsed6a438Na/0J dSJQ== X-Gm-Message-State: APjAAAWqVIzTL4XnUlE6mfhxjOCW49R79u9eG8XXOVpnveTT6ff402xG btUSJVmMV/nCreO/DSu6F3Yh8A== X-Google-Smtp-Source: APXvYqxa8NPQpW/ncEZ+9wWZVsY/YQvADDPz4jjl5yyTTQ0yaFx82hxstv7CK/gJQmit6jtF7CSy+w== X-Received: by 2002:a17:90a:b294:: with SMTP id c20mr7807965pjr.16.1560463009452; Thu, 13 Jun 2019 14:56:49 -0700 (PDT) Received: from localhost ([2620:15c:202:1:75a:3f6e:21d:9374]) by smtp.gmail.com with ESMTPSA id v28sm687528pga.65.2019.06.13.14.56.48 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 13 Jun 2019 14:56:48 -0700 (PDT) Date: Thu, 13 Jun 2019 14:56:46 -0700 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 Subject: Re: [PATCH 2/4] backlight: Expose brightness curve type through sysfs Message-ID: <20190613215646.GO137143@google.com> References: <20190613194326.180889-1-mka@chromium.org> <20190613194326.180889-3-mka@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190613194326.180889-3-mka@chromium.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I noticed a few minor things when glancing over the patch on patchwork On Thu, Jun 13, 2019 at 12:43:24PM -0700, Matthias Kaehlcke wrote: > Backlight brightness curves can have different shapes. The two main > types are linear and non-linear curves. The human eye doesn't > perceive linearly increasing/decreasing brightness as linear (see > also 88ba95bedb79 "backlight: pwm_bl: Compute brightness of LED > linearly to human eye"), hence many backlights use non-linear (often > logarithmic) brightness curves. The type of curve currently is opaque > to userspace, so userspace often relies on more or less reliable nit: avoid relies ... reliable :) > heuristics (like the number of brightness levels) to decide whether > to treat a backlight device as linear or non-linear. > > Export the type of the brightness curve via the new sysfs attribute > 'scale'. The value of the attribute may be a simple string like > 'linear' or 'non-linear', or a composite string similar to > 'compatible' strings of the device tree. A composite string consists > of different elements separated by commas, starting with the > most-detailed description and ending with the least-detailed one. An > example for a composite string is "cie-1931,perceptual,non-linear" > This brightness curve was generated with the CIE 1931 algorithm, it > is perceptually linear, but not actually linear in terms of the > emitted light. If userspace doesn't know about 'cie-1931' or > 'perceptual' it should at least be able to interpret the 'non-linear' > part. > > For devices that don't provide information about the scale of their > brightness curve the value of the 'scale' attribute is 'unknown'. > > Signed-off-by: Matthias Kaehlcke > --- > .../ABI/testing/sysfs-class-backlight | 32 +++++++++++++++++++ > MAINTAINERS | 1 + > drivers/video/backlight/backlight.c | 22 +++++++++++++ > include/linux/backlight.h | 10 ++++++ > 4 files changed, 65 insertions(+) > create mode 100644 Documentation/ABI/testing/sysfs-class-backlight > > diff --git a/Documentation/ABI/testing/sysfs-class-backlight b/Documentation/ABI/testing/sysfs-class-backlight > new file mode 100644 > index 000000000000..924fb68940e6 > --- /dev/null > +++ b/Documentation/ABI/testing/sysfs-class-backlight > @@ -0,0 +1,32 @@ > +What: /sys/class/backlight//scale > +Date: June 2019 > +KernelVersion: 5.4 > +Contact: Daniel Thompson > +Description: > + Description of the scale of the brightness curve. The > + description consists of one or more elements separated by > + commas, from the most detailed to the least detailed > + description. > + > + Possible values are: > + > + unknown > + The scale of the brightness curve is unknown. > + > + linear > + The brightness changes linearly in terms of the emitted > + light, changes are perceived as non-linear by the human eye. > + > + non-linear > + The brightness changes non-linearly in terms of the emitted > + light, changes might be perceived as linear by the human eye. > + > + perceptual,non-linear > + The brightness changes non-linearly in terms of the emitted > + light, changes should be perceived as linear by the human eye. > + > + cie-1931,perceptual,non-linear > + The brightness curves was calculated with the CIE 1931 s/curves/curve/ > +static const char *const backlight_scale_types[] = { > + [BACKLIGHT_SCALE_UNKNOWN] = "unknown", > + [BACKLIGHT_SCALE_CIE1931] = "cie-1931,perceptual,non-linear", > + [BACKLIGHT_SCALE_PERCEPTUAL] = "perceptual,non-linear", > + [BACKLIGHT_SCALE_LINEAR] = "linear", > + [BACKLIGHT_SCALE_NON_LINEAR] = "non-linear", > +}; > + > + Delete one blank line > +enum backlight_scale { > + BACKLIGHT_SCALE_UNKNOWN, > + BACKLIGHT_SCALE_CIE1931 = 1, > + BACKLIGHT_SCALE_PERCEPTUAL, > + BACKLIGHT_SCALE_LINEAR, > + BACKLIGHT_SCALE_NON_LINEAR, /* needed for backwards compatibility */ maybe better list the more generic options first, same for the string table.