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 2204EC433F5 for ; Fri, 1 Oct 2021 22:54:39 +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 DACB661246 for ; Fri, 1 Oct 2021 22:54:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org DACB661246 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 928656F41F; Fri, 1 Oct 2021 22:54:31 +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 9C17F6F41C for ; Fri, 1 Oct 2021 22:54:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633128868; 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=BsJPANeDgIl93WRVHxlK0bX6Rfs1wxpLbl3miVk2BhhX6CO8UcQJ3WJA6Eus1y1a8MV3ef qLWHjg/P+IGVVjhT1Tmv0HrtpXLBgnPQdll9Xwqi9Ut3HJu+Jz0BV/xuna37VSURAkOF7J Hf8WiTSbFePulEZ1PuB8zCqKV9kBN1E= 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-591-aJNvwhkgOdiqKhSLA8JLJg-1; Fri, 01 Oct 2021 18:54:27 -0400 X-MC-Unique: aJNvwhkgOdiqKhSLA8JLJg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E8F351023F4E; Fri, 1 Oct 2021 22:54:25 +0000 (UTC) Received: from Ruby.redhat.com (unknown [10.22.17.71]) by smtp.corp.redhat.com (Postfix) with ESMTP id 95F3160BF1; Fri, 1 Oct 2021 22:54:24 +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: Fri, 1 Oct 2021 18:53:44 -0400 Message-Id: <20211001225344.1752203-5-lyude@redhat.com> In-Reply-To: <20211001225344.1752203-1-lyude@redhat.com> References: <20211001225344.1752203-1-lyude@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Subject: [Nouveau] [PATCH v2 4/4] 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