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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 98912C433FE for ; Wed, 6 Oct 2021 02:41:56 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6C2E76115A for ; Wed, 6 Oct 2021 02:41:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 6C2E76115A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 7824F6ECCC; Wed, 6 Oct 2021 02:41:45 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by gabe.freedesktop.org (Postfix) with ESMTPS id E30A56ECD9 for ; Wed, 6 Oct 2021 02:41:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633488103; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VRuibAzD4usxTf8vGq2IshPiQf0ZGBrLjbZl7aosdOQ=; b=a5ZxUFySISOOQmywBwlWOB55y21jcfkTjdRjDXiIbD7ClbZVfM7u/gZ9ls+PlyHcoN6Tn4 5cSfRwGZaRx+FRV09ghAH5j6g6+B1AVYAb8bGmBE8DmikT4mi6lzV0NQXF/ZOeyK35Kbsw RP8KVOssUBTedfO2J0eqNhDYqMQBxxQ= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-212-TsyCj4yHPCe0F15gYLyScg-1; Tue, 05 Oct 2021 22:41:39 -0400 X-MC-Unique: TsyCj4yHPCe0F15gYLyScg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4AF88802C88; Wed, 6 Oct 2021 02:41:38 +0000 (UTC) Received: from Ruby.lyude.net (unknown [10.22.16.47]) by smtp.corp.redhat.com (Postfix) with ESMTP id 511799AA2E; Wed, 6 Oct 2021 02:41:36 +0000 (UTC) From: Lyude Paul To: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org Cc: Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , David Airlie , Daniel Vetter , =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= , Sean Paul , linux-kernel@vger.kernel.org (open list) Date: Tue, 5 Oct 2021 22:40:18 -0400 Message-Id: <20211006024018.320394-6-lyude@redhat.com> In-Reply-To: <20211006024018.320394-1-lyude@redhat.com> References: <20211006024018.320394-1-lyude@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Subject: [Nouveau] [PATCH v3 5/5] drm/i915: Clarify probing order in intel_dp_aux_init_backlight_funcs() X-BeenThere: nouveau@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Nouveau development list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: nouveau-bounces@lists.freedesktop.org Sender: "Nouveau" Hooray! We've managed to hit enough bugs upstream that I've been able to come up with a pretty solid explanation for how backlight controls are actually supposed to be detected and used these days. As well, having the rest of the PWM bits in VESA's backlight interface implemented seems to have fixed all of the problematic brightness controls laptop panels that we've hit so far. So, let's actually document this instead of just calling the laptop panels liars. As well, I would like to formally apologize to all of the laptop panels I called liars. I'm sorry laptop panels, hopefully you can all forgive me and we can move past this~ Signed-off-by: Lyude Paul --- .../drm/i915/display/intel_dp_aux_backlight.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c index 91daf9ab50e8..04a52d6a74ed 100644 --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c @@ -455,11 +455,17 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector) } /* - * A lot of eDP panels in the wild will report supporting both the - * Intel proprietary backlight control interface, and the VESA - * backlight control interface. Many of these panels are liars though, - * and will only work with the Intel interface. So, always probe for - * that first. + * Since Intel has their own backlight control interface, the majority of machines out there + * using DPCD backlight controls with Intel GPUs will be using this interface as opposed to + * the VESA interface. However, other GPUs (such as Nvidia's) will always use the VESA + * interface. This means that there's quite a number of panels out there that will advertise + * support for both interfaces, primarily systems with Intel/Nvidia hybrid GPU setups. + * + * There's a catch to this though: on many panels that advertise support for both + * interfaces, the VESA backlight interface will stop working once we've programmed the + * panel with Intel's OUI - which is also required for us to be able to detect Intel's + * backlight interface at all. This means that the only sensible way for us to detect both + * interfaces is to probe for Intel's first, and VESA's second. */ if (try_intel_interface && intel_dp_aux_supports_hdr_backlight(connector)) { drm_dbg_kms(dev, "Using Intel proprietary eDP backlight controls\n"); -- 2.31.1