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=-9.8 required=3.0 tests=BAYES_00,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 autolearn=unavailable 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 9AC88C43461 for ; Thu, 10 Sep 2020 07:48:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 30A5820809 for ; Thu, 10 Sep 2020 07:48:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ffwll.ch header.i=@ffwll.ch header.b="NU3t/lYA" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727791AbgIJHsM (ORCPT ); Thu, 10 Sep 2020 03:48:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49808 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726846AbgIJHsE (ORCPT ); Thu, 10 Sep 2020 03:48:04 -0400 Received: from mail-wr1-x444.google.com (mail-wr1-x444.google.com [IPv6:2a00:1450:4864:20::444]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A5013C061757 for ; Thu, 10 Sep 2020 00:48:02 -0700 (PDT) Received: by mail-wr1-x444.google.com with SMTP id g4so5578822wrs.5 for ; Thu, 10 Sep 2020 00:48:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=date:from:to:cc:subject:message-id:mail-followup-to:references :mime-version:content-disposition:in-reply-to; bh=EzwOJPxFQZYC72dKxH1QwXbLeAK6MXsJW34CXePZsDk=; b=NU3t/lYA4IuNCNtpekqscA2TyplAkzfP+R8MUCR3PvCAb8uJiYk1wOzzb8wwXS4UMr DVA4tRl1Ve9Exjbx9S/0pONj/l6Gmg8wchly5ZcfOeQgRhaHAGu83K0TF5f78u/Lc85y hkhIHeTu8rvomAvVXj5waA1W35Dcxm1hJK7BI= 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 :mail-followup-to:references:mime-version:content-disposition :in-reply-to; bh=EzwOJPxFQZYC72dKxH1QwXbLeAK6MXsJW34CXePZsDk=; b=GwgdykXe/OA1HlCuqQFOD3e2h5h1CCZmNdXP8bKh1SA67Ocidi3eDK7O/JcjSOKjfF R06sY4n9SRsC0xZ3NPFtipEU6/KUgUQPdHZ8rH/ryJ9pWm1Wd13QwSywSZrN3lPW4Y0P 8iMakx+8075jqvnrKAaYeIHp0RE5XESGMFalCpF8SweOdr8Ay6OHHImD6jQmmRajI+Ck 0nwYcUke+dt7OwbJV5UJk2moV/SvjeRTjnlbTChOk6BAf5V2Q7JJ7PVLurW/p1XDIC/t UiS8lMOKml0BvtMjbe3P+zOYz/0wa1EMKImViR+WB1h4TSVKC5bGj4YTxCPMl8wRCPNu xFWw== X-Gm-Message-State: AOAM5314/e5shlJMNYPOIyICpAj+i1w8JxyNbmpfoyOnth5yTucmLaPw ER2jOTAMs7FavisFtqnM5dW9DQ== X-Google-Smtp-Source: ABdhPJyHnNn0zGerD4FHfuyk3jfmyvmU9pJsJ0jZ9yhN7+q1Nh4texQADwMpFBCQe7+lPrgnAcEOvw== X-Received: by 2002:a5d:4247:: with SMTP id s7mr7407060wrr.167.1599724079550; Thu, 10 Sep 2020 00:47:59 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id h204sm2348153wmf.35.2020.09.10.00.47.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Sep 2020 00:47:58 -0700 (PDT) Date: Thu, 10 Sep 2020 09:47:56 +0200 From: Daniel Vetter To: Daniel Thompson Cc: Alexandru Stan , linux-pwm , Linux Fbdev development list , Bartlomiej Zolnierkiewicz , Jingoo Han , Douglas Anderson , Rob Herring , Linux Kernel Mailing List , Thierry Reding , dri-devel , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Enric Balletbo i Serra , Lee Jones , Matthias Kaehlcke Subject: Re: [PATCH 2/3] backlight: pwm_bl: Artificially add 0% during interpolation Message-ID: <20200910074756.GE438822@phenom.ffwll.local> Mail-Followup-To: Daniel Thompson , Alexandru Stan , linux-pwm , Linux Fbdev development list , Bartlomiej Zolnierkiewicz , Jingoo Han , Douglas Anderson , Rob Herring , Linux Kernel Mailing List , Thierry Reding , dri-devel , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Enric Balletbo i Serra , Lee Jones , Matthias Kaehlcke References: <20200721042522.2403410-1-amstan@chromium.org> <20200720212502.2.Iab4d2192e4cf50226e0a58d58df7d90ef92713ce@changeid> <20200904113822.xoyt4w5x7vwvh7cr@holly.lan> <20200907075018.GM2352366@phenom.ffwll.local> <20200909144537.daq2exfihhxm6bai@holly.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Operating-System: Linux phenom 5.7.0-1-amd64 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 09, 2020 at 05:03:37PM +0200, Daniel Vetter wrote: > On Wed, Sep 9, 2020 at 4:45 PM Daniel Thompson > wrote: > > > > On Mon, Sep 07, 2020 at 09:50:18AM +0200, Daniel Vetter wrote: > > > On Fri, Sep 04, 2020 at 12:38:22PM +0100, Daniel Thompson wrote: > > > > On Mon, Jul 20, 2020 at 09:25:21PM -0700, Alexandru Stan wrote: > > > > > Some displays need the low end of the curve cropped in order to make > > > > > them happy. In that case we still want to have the 0% point, even though > > > > > anything between 0% and 5%(example) would be skipped. > > > > > > > > For backlights it is not defined that 0 means off and, to be honest, 0 > > > > means off is actually rather weird for anything except transflexive > > > > or front lit reflective displays[1]. There is a problem on several > > > > systems that when the backlight slider is reduced to zero you can't > > > > see the screen properly to turn it back up. This patch looks like it > > > > would make that problem worse by hurting systems with will written > > > > device trees. > > > > > > > > There is some nasty legacy here: some backlight displays that are off > > > > at zero and that sucks because userspace doesn't know whether zero is > > > > off or lowest possible setting. > > > > > > > > Nevertheless perhaps a better way to handle this case is for 0 to map to > > > > 5% power and for the userspace to turn the backlight on/off as final > > > > step in an animated backlight fade out (and one again for a fade in). > > > > > > Afaik chromeos encodes "0 means off" somewhere in there stack. We've > > > gotten similar patches for the i915 backlight driver when we started > > > obeying the panel's lower limit in our pwm backlight driver thing that's > > > sometimes used instead of acpi. > > > > Out of interest... were they accepted? > > > > I did took a quick look at intel_panel.c and didn't see anything > > that appeared to be special casing zero but I thought I might double > > check. > > I don't think so. Just figured I bring this up since it might explain > why this is coming back again from an @chromium.com address. Thanks to Alexandru pointing at the right code it's clear this got fix, over 5 years ago: https://source.chromium.org/chromiumos/_/chromium/chromiumos/platform2/+/6e83a6a8bb772ed8a2f939da1c7a152147c12789 power: Write to bl_power when backlight reaches or leaves 0. Make InternalBacklight write FB_BLANK_UNBLANK to bl_power just before setting the internal backlight brightness to a nonzero value, and FB_BLANK_POWERDOWN to bl_power just before setting the brightness to 0. This is needed for hardware that interprets a brightness level of 0 as meaning "dim" rather than "off". BUG=chromium:396218 TEST=added unit tests Change-Id: I914e333ab41db623564d5a67beac89f1a62bce9d Reviewed-on: https://chromium-review.googlesource.com/311010 Commit-Ready: Dan Erat Tested-by: Dan Erat Reviewed-by: Dan Erat Cheers, Daniel > > > There's also the problem that with fancy panels with protocol (dsi, edp, > > > ...) shutting of the backlight completely out of the proper power sequence > > > hangs the panel (for some panels at least), so providing a backlight off > > > that doesn't go through the drm modeset sequence isn't always possible. > > > > > > It's a bit a mess indeed :-/ > > > -Daniel > > > > > > > > > > > > > > > Daniel. > > > > > > > > > > > > > > Signed-off-by: Alexandru Stan > > > > > --- > > > > > > > > > > drivers/video/backlight/pwm_bl.c | 8 ++++++++ > > > > > 1 file changed, 8 insertions(+) > > > > > > > > > > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c > > > > > index 5193a72305a2..b24711ddf504 100644 > > > > > --- a/drivers/video/backlight/pwm_bl.c > > > > > +++ b/drivers/video/backlight/pwm_bl.c > > > > > @@ -349,6 +349,14 @@ static int pwm_backlight_parse_dt(struct device *dev, > > > > > /* Fill in the last point, since no line starts here. */ > > > > > table[x2] = y2; > > > > > > > > > > + /* > > > > > + * If we don't start at 0 yet we're increasing, assume > > > > > + * the dts wanted to crop the low end of the range, so > > > > > + * insert a 0 to provide a display off mode. > > > > > + */ > > > > > + if (table[0] > 0 && table[0] < table[num_levels - 1]) > > > > > + table[0] = 0; > > > > > + > > > > > /* > > > > > * As we use interpolation lets remove current > > > > > * brightness levels table and replace for the > > > > > -- > > > > > 2.27.0 > > > > _______________________________________________ > > > > dri-devel mailing list > > > > dri-devel@lists.freedesktop.org > > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > > > > -- > > > Daniel Vetter > > > Software Engineer, Intel Corporation > > > http://blog.ffwll.ch > > _______________________________________________ > > dri-devel mailing list > > dri-devel@lists.freedesktop.org > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch