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=-5.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 CCF15C3A5A0 for ; Mon, 19 Aug 2019 18:56:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9ADD9214DA for ; Mon, 19 Aug 2019 18:56:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="WbPRIlO5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728283AbfHSS4d (ORCPT ); Mon, 19 Aug 2019 14:56:33 -0400 Received: from mail-pl1-f196.google.com ([209.85.214.196]:37249 "EHLO mail-pl1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727957AbfHSS4c (ORCPT ); Mon, 19 Aug 2019 14:56:32 -0400 Received: by mail-pl1-f196.google.com with SMTP id bj8so1400938plb.4 for ; Mon, 19 Aug 2019 11:56:32 -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=C0e2APdFMcCL115V7DOVVJSnlHloFclNY39dd69/lO0=; b=WbPRIlO58ztUhi7i2oz12gIxghvYFhvGj5detvHL64ciojw1Jbh1rIUinASAN5D8ZH oktM00ScxqNk41KTkk3qw/+BHQPD4Q3wJeTI1oV2U3gwQatbTu8PX10ZFmAfuarYSyE2 ivJrpHi6loe1F9bmEmdOWwWzx2oF50n/ZrQtM= 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=C0e2APdFMcCL115V7DOVVJSnlHloFclNY39dd69/lO0=; b=eDihlBKdB1r2JJ8kdmpT06xUGCZCuNCdsa3hNEDnyMOAeHL8IxVC28lJasJ5/PQXNy iglkFpEpH+pYFC9Eyc2IAOu7XJ3awO1IaWrznX4ZnvwREmuQlDtYCiPBC3trg8zDVEqu eOY2SOaRrcgmTwHboykThFPfrOLA332nw/yikOsaY3ElX8iOP4A6HSEOhZr/xO75HjE6 Hy2sbAzOri/GlZ5tXCCkiy0qLc+/XTPqt+y4ZdnquXfa/2UAXcbH3V6hgO3Nm62oyHxt Jpi5uWz3UKrWs9ULu2OyZFhUiKp1el/JHtlxm7z/LT/aBERuEPSh+ByZPVJIR+JnosGN w0XQ== X-Gm-Message-State: APjAAAWfhiwGqwBpwNA6Jp7ZqyI0LEYZ5U7WubUT6Y4iSQGgOpXAbmJH 2WpAHMQBEhyRI5i4rfKTNS4X0Q== X-Google-Smtp-Source: APXvYqxh+E8TFUryXTjcfNmp7eEgV3tGYzniOp22FCvAHtBGpb7ARiJTtlOQVWkRBrXizfRtmjdGHw== X-Received: by 2002:a17:902:788b:: with SMTP id q11mr24093153pll.308.1566240655357; Mon, 19 Aug 2019 11:50:55 -0700 (PDT) Received: from localhost ([2620:15c:202:1:75a:3f6e:21d:9374]) by smtp.gmail.com with ESMTPSA id x25sm18660949pfa.90.2019.08.19.11.50.54 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 19 Aug 2019 11:50:54 -0700 (PDT) Date: Mon, 19 Aug 2019 11:50:49 -0700 From: Matthias Kaehlcke To: Daniel Thompson Cc: Thierry Reding , Lee Jones , Jingoo Han , Bartlomiej Zolnierkiewicz , 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 v3 2/4] backlight: Expose brightness curve type through sysfs Message-ID: <20190819185049.GZ250418@google.com> References: <20190709190007.91260-1-mka@chromium.org> <20190709190007.91260-3-mka@chromium.org> <20190807201528.GO250418@google.com> <510f6d8a-71a0-fa6e-33ea-c4a4bfa96607@linaro.org> <20190816175317.GU250418@google.com> <20190819100241.5pctjxmsq6crlale@holly.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190819100241.5pctjxmsq6crlale@holly.lan> 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 Hi Daniel, On Mon, Aug 19, 2019 at 11:02:41AM +0100, Daniel Thompson wrote: > On Fri, Aug 16, 2019 at 10:53:17AM -0700, Matthias Kaehlcke wrote: > > On Fri, Aug 16, 2019 at 04:54:18PM +0100, Daniel Thompson wrote: > > > On 07/08/2019 21:15, Matthias Kaehlcke wrote: > > > > On Tue, Jul 09, 2019 at 12:00:05PM -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 uses more or less 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 can be 'linear', 'non-linear' or > > > > > 'unknown'. 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 > > > > > > > > Daniel (et al): do you have any more comments on this patch/series or > > > > is it ready to land? > > > > > > I decided to leave it for a long while for others to review since I'm still > > > a tiny bit uneasy about the linear/non-linear terminology. > > > > > > However that's my only concern, its fairly minor and I've dragged by feet > > > for more then long enough, so: > > > Reviewed-by: Daniel Thompson > > > > Thanks! > > > > If you or someone else has another suggestion for the terminology that > > we can all agree on I'm happy to change it. > > As you will see in my reply to Uwe. The term I tend to adopt when I want > to be precise about userspace behaviour is "perceptual" (e.g. that a > backlight can be mapped directly to a slider and it will feel right). > > However that raises its own concerns: mostly about what is perceptual > enough. > > Clear the automatic brightness curve support in the PWM driver is > perceptual. > > To be honest I suspect that in most cases a true logarithmic curve (given a > sane exponent) would be perceptual enough. In other words it will feel > comfortable with a direct mapped slider and using it for animation > won't be too bad. > > However when we get right down to it *that* is the information that is > actually most useful to userspace: explicit confirmation that the scale > can be mapped directly to a slider. I think it also aligned better with > Uwe's feedback (e.g. to start working towards having a preferred scale). IIUC the conclusion is that there is no need for a string attribute because we only need to distinguish between 'perceptual' and 'non-perceptual'. If that is correct, do you have any preference for the attribute name ('perceptual_scale', 'perceptual', ...)? From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthias Kaehlcke Subject: Re: [PATCH v3 2/4] backlight: Expose brightness curve type through sysfs Date: Mon, 19 Aug 2019 11:50:49 -0700 Message-ID: <20190819185049.GZ250418@google.com> References: <20190709190007.91260-1-mka@chromium.org> <20190709190007.91260-3-mka@chromium.org> <20190807201528.GO250418@google.com> <510f6d8a-71a0-fa6e-33ea-c4a4bfa96607@linaro.org> <20190816175317.GU250418@google.com> <20190819100241.5pctjxmsq6crlale@holly.lan> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Content-Disposition: inline In-Reply-To: <20190819100241.5pctjxmsq6crlale@holly.lan> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Daniel Thompson Cc: linux-pwm@vger.kernel.org, linux-fbdev@vger.kernel.org, Bartlomiej Zolnierkiewicz , Jingoo Han , Brian Norris , linux-kernel@vger.kernel.org, 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dCB0aGUgc2NhbGUKPiBjYW4gYmUgbWFwcGVkIGRpcmVjdGx5IHRvIGEgc2xpZGVyLiBJIHRoaW5r IGl0IGFsc28gYWxpZ25lZCBiZXR0ZXIgd2l0aAo+IFV3ZSdzIGZlZWRiYWNrIChlLmcuIHRvIHN0 YXJ0IHdvcmtpbmcgdG93YXJkcyBoYXZpbmcgYSBwcmVmZXJyZWQgc2NhbGUpLgoKSUlVQyB0aGUg Y29uY2x1c2lvbiBpcyB0aGF0IHRoZXJlIGlzIG5vIG5lZWQgZm9yIGEgc3RyaW5nIGF0dHJpYnV0 ZQpiZWNhdXNlIHdlIG9ubHkgbmVlZCB0byBkaXN0aW5ndWlzaCBiZXR3ZWVuICdwZXJjZXB0dWFs JyBhbmQKJ25vbi1wZXJjZXB0dWFsJy4gSWYgdGhhdCBpcyBjb3JyZWN0LCBkbyB5b3UgaGF2ZSBh bnkgcHJlZmVyZW5jZSBmb3IKdGhlIGF0dHJpYnV0ZSBuYW1lICgncGVyY2VwdHVhbF9zY2FsZScs ICdwZXJjZXB0dWFsJywgLi4uKT8KX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fX19fX18KZHJpLWRldmVsIG1haWxpbmcgbGlzdApkcmktZGV2ZWxAbGlzdHMuZnJlZWRl c2t0b3Aub3JnCmh0dHBzOi8vbGlzdHMuZnJlZWRlc2t0b3Aub3JnL21haWxtYW4vbGlzdGluZm8v ZHJpLWRldmVs From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthias Kaehlcke Date: Mon, 19 Aug 2019 18:50:49 +0000 Subject: Re: [PATCH v3 2/4] backlight: Expose brightness curve type through sysfs Message-Id: <20190819185049.GZ250418@google.com> List-Id: References: <20190709190007.91260-1-mka@chromium.org> <20190709190007.91260-3-mka@chromium.org> <20190807201528.GO250418@google.com> <510f6d8a-71a0-fa6e-33ea-c4a4bfa96607@linaro.org> <20190816175317.GU250418@google.com> <20190819100241.5pctjxmsq6crlale@holly.lan> In-Reply-To: <20190819100241.5pctjxmsq6crlale@holly.lan> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Daniel Thompson Cc: linux-pwm@vger.kernel.org, linux-fbdev@vger.kernel.org, Bartlomiej Zolnierkiewicz , Jingoo Han , Brian Norris , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Douglas Anderson , Thierry Reding , Jacek Anaszewski , Pavel Machek , Enric Balletbo i Serra , Lee Jones Hi Daniel, On Mon, Aug 19, 2019 at 11:02:41AM +0100, Daniel Thompson wrote: > On Fri, Aug 16, 2019 at 10:53:17AM -0700, Matthias Kaehlcke wrote: > > On Fri, Aug 16, 2019 at 04:54:18PM +0100, Daniel Thompson wrote: > > > On 07/08/2019 21:15, Matthias Kaehlcke wrote: > > > > On Tue, Jul 09, 2019 at 12:00:05PM -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 uses more or less 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 can be 'linear', 'non-linear' or > > > > > 'unknown'. 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 > > > > > > > > Daniel (et al): do you have any more comments on this patch/series or > > > > is it ready to land? > > > > > > I decided to leave it for a long while for others to review since I'm still > > > a tiny bit uneasy about the linear/non-linear terminology. > > > > > > However that's my only concern, its fairly minor and I've dragged by feet > > > for more then long enough, so: > > > Reviewed-by: Daniel Thompson > > > > Thanks! > > > > If you or someone else has another suggestion for the terminology that > > we can all agree on I'm happy to change it. > > As you will see in my reply to Uwe. The term I tend to adopt when I want > to be precise about userspace behaviour is "perceptual" (e.g. that a > backlight can be mapped directly to a slider and it will feel right). > > However that raises its own concerns: mostly about what is perceptual > enough. > > Clear the automatic brightness curve support in the PWM driver is > perceptual. > > To be honest I suspect that in most cases a true logarithmic curve (given a > sane exponent) would be perceptual enough. In other words it will feel > comfortable with a direct mapped slider and using it for animation > won't be too bad. > > However when we get right down to it *that* is the information that is > actually most useful to userspace: explicit confirmation that the scale > can be mapped directly to a slider. I think it also aligned better with > Uwe's feedback (e.g. to start working towards having a preferred scale). IIUC the conclusion is that there is no need for a string attribute because we only need to distinguish between 'perceptual' and 'non-perceptual'. If that is correct, do you have any preference for the attribute name ('perceptual_scale', 'perceptual', ...)?