From patchwork Mon Sep 27 20:12:06 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lyude Paul X-Patchwork-Id: 12520713 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 2349DC433F5 for ; Mon, 27 Sep 2021 20:13:00 +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 E809860FF2 for ; Mon, 27 Sep 2021 20:12:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org E809860FF2 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 8D6B66E85E; Mon, 27 Sep 2021 20:12:51 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by gabe.freedesktop.org (Postfix) with ESMTPS id 27D756E03E for ; Mon, 27 Sep 2021 20:12:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1632773566; 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=skkbLXdqWZa0OlDaidm6eR+nQIQyI/93FeXhSOp26Z8=; b=gAoaS/5OR76Nsm3PBXFzxLyUsR8HbH5xo9ky5BtLkIMBQvDA2cCDH1UyVe+3aPSIYkAXZl mC7DC334oKJXYR6E0qN0ZvfJ66Ge7HN3J1RZt4D7kFuRgGjONBmB/TUh8AxA+vqGHrWTh7 dey10bsuO0VbKpeiVfzzPecIpv3dxz4= 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-599-vMAX0IiuMhKBo2akEbWmDg-1; Mon, 27 Sep 2021 16:12:45 -0400 X-MC-Unique: vMAX0IiuMhKBo2akEbWmDg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E3AFD802921; Mon, 27 Sep 2021 20:12:43 +0000 (UTC) Received: from Ruby.lyude.net (unknown [10.22.17.167]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8BE7510074EF; Mon, 27 Sep 2021 20:12:42 +0000 (UTC) From: Lyude Paul To: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org Cc: Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , David Airlie , Daniel Vetter , =?utf-8?b?VmlsbGUgU3lyasOkbMOk?= , Sean Paul , linux-kernel@vger.kernel.org (open list) Subject: [PATCH 3/3] drm/i915: Clarify probing order in intel_dp_aux_init_backlight_funcs() Date: Mon, 27 Sep 2021 16:12:06 -0400 Message-Id: <20210927201206.682788-4-lyude@redhat.com> In-Reply-To: <20210927201206.682788-1-lyude@redhat.com> References: <20210927201206.682788-1-lyude@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" 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 9b1ac02b0263..1e20c607408c 100644 --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c @@ -456,11 +456,17 @@ 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");