From patchwork Fri Nov 5 18:33:42 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Lyude Paul X-Patchwork-Id: 12605217 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 A2680C4332F for ; Fri, 5 Nov 2021 18:34:38 +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 7125161131 for ; Fri, 5 Nov 2021 18:34:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 7125161131 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 F1DB76ECA2; Fri, 5 Nov 2021 18:34:36 +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 543436ECA2 for ; Fri, 5 Nov 2021 18:34:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1636137274; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+zTpBMvFXVwp0cVfmRszlrLDuyQaiT/zVOksqphYoeg=; b=GflOLOBKhWJHy0FpjEYCQJKEgOvq0xzGu6dYNlkbL1SF0eEoidSibKwUDmx6Zi83BUnZIH zsrX0ngY2eY7o/tHO6g0OgiTH1Wh7QF91LQPFJDg+ef1gQYWgqTkwNkGbf2xPgoigl9U/+ 9j/lFppR+Ogy61ituwtzmvlxUEL/dVw= 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-120-UfKaqCuwOPWibbIvzcbeAQ-1; Fri, 05 Nov 2021 14:34:29 -0400 X-MC-Unique: UfKaqCuwOPWibbIvzcbeAQ-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 E053E1006AA2; Fri, 5 Nov 2021 18:34:27 +0000 (UTC) Received: from emerald.lyude.net (unknown [10.22.16.200]) by smtp.corp.redhat.com (Postfix) with ESMTP id E5B735FC13; Fri, 5 Nov 2021 18:34:24 +0000 (UTC) From: Lyude Paul To: dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org, intel-gfx@lists.freedesktop.org Subject: [PATCH v5 5/5] drm/i915: Clarify probing order in intel_dp_aux_init_backlight_funcs() Date: Fri, 5 Nov 2021 14:33:42 -0400 Message-Id: <20211105183342.130810-6-lyude@redhat.com> In-Reply-To: <20211105183342.130810-1-lyude@redhat.com> References: <20211105183342.130810-1-lyude@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 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: , Cc: Tvrtko Ursulin , David Airlie , open list , Rodrigo Vivi 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 Acked-by: Ville Syrjälä --- .../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 96fe3eaba44a..8b9c925c4c16 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");