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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 04235C33CB1 for ; Fri, 17 Jan 2020 11:50:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D348A2072B for ; Fri, 17 Jan 2020 11:50:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727008AbgAQLuh (ORCPT ); Fri, 17 Jan 2020 06:50:37 -0500 Received: from mga09.intel.com ([134.134.136.24]:35138 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726689AbgAQLug (ORCPT ); Fri, 17 Jan 2020 06:50:36 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 17 Jan 2020 03:48:01 -0800 X-IronPort-AV: E=Sophos;i="5.70,330,1574150400"; d="scan'208";a="218886700" Received: from jnikula-mobl3.fi.intel.com (HELO localhost) ([10.237.66.161]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 17 Jan 2020 03:47:56 -0800 From: Jani Nikula To: Lyude Paul , intel-gfx@lists.freedesktop.org Cc: dri-devel@lists.freedesktop.org, Perry Yuan , AceLan Kao , Joonas Lahtinen , Rodrigo Vivi , David Airlie , Daniel Vetter , Chris Wilson , Ville =?utf-8?B?U3lyasOkbMOk?= , Juha-Pekka Heikkila , Lee Shawn C , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 4/5] drm/i915: Don't use VBT for detecting DPCD backlight controls In-Reply-To: <87zhemgvrn.fsf@intel.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo References: <20200116211623.53799-1-lyude@redhat.com> <20200116211623.53799-5-lyude@redhat.com> <87zhemgvrn.fsf@intel.com> Date: Fri, 17 Jan 2020 13:47:53 +0200 Message-ID: <87wo9qgv86.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 17 Jan 2020, Jani Nikula wrote: > On Thu, 16 Jan 2020, Lyude Paul wrote: >> Despite the fact that the VBT appears to have a field for specifying >> that a system is equipped with a panel that supports standard VESA >> backlight controls over the DP AUX channel, so far every system we've >> spotted DPCD backlight control support on doesn't actually set this >> field correctly and all have it set to INTEL_BACKLIGHT_DISPLAY_DDI. >> >> While we don't know the exact reason for this VBT misuse, talking with >> some vendors indicated that there's a good number of laptop panels out >> there that supposedly support both PWM backlight controls and DPCD >> backlight controls as a workaround until Intel supports DPCD backlight >> controls across platforms universally. This being said, the X1 Extreme >> 2nd Gen that I have here (note that Lenovo is not the hardware vendor >> that informed us of this) PWM backlight controls are advertised, but >> only DPCD controls actually function. I'm going to make an educated >> guess here and say that on systems like this one, it's likely that PWM >> backlight controls might have been intended to work but were never >> really tested by QA. >> >> Since we really need backlights to work without any extra module >> parameters, let's take the risk here and rely on the standard DPCD caps >> to tell us whether AUX backlight controls are supported or not. We still >> check the VBT, but only to make sure that we don't enable DPCD backlight >> controls on a panel that uses something other then the standard VESA >> interfaces over AUX. Since panels using such non-standard interfaces >> should probably have support added to i915, we'll print a warning when >> seeing this in the VBT. We can remove this warning later if we end up >> adding support for any custom backlight interfaces. >> >> Signed-off-by: Lyude Paul >> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112376 >> Cc: Jani Nikula >> Cc: Perry Yuan >> Cc: AceLan Kao >> --- >> .../drm/i915/display/intel_dp_aux_backlight.c | 16 ++++++++++------ >> 1 file changed, 10 insertions(+), 6 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 77a759361c5c..3002b600635f 100644 >> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c >> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c >> @@ -330,13 +330,17 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector) >> struct intel_panel *panel = &intel_connector->panel; >> struct drm_i915_private *dev_priv = to_i915(intel_connector->base.dev); >> >> - if (i915_modparams.enable_dpcd_backlight == 0 || >> - (i915_modparams.enable_dpcd_backlight == -1 && >> - dev_priv->vbt.backlight.type != INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE)) >> - return -ENODEV; >> - >> - if (!intel_dp_aux_display_control_capable(intel_connector)) >> + if (i915_modparams.enable_dpcd_backlight == 0) >> return -ENODEV; >> + if (i915_modparams.enable_dpcd_backlight == -1) { >> + if (dev_priv->vbt.backlight.type >> + == INTEL_BACKLIGHT_PANEL_DRIVER_INTERFACE) { >> + DRM_WARN("VBT says panel uses custom panel driver interface, not using DPCD backlight controls\n"); >> + return -ENODEV; >> + } >> + if (!intel_dp_aux_display_control_capable(intel_connector)) >> + return -ENODEV; > > Functionally, I'm fine with trying this. But perhaps we should check aux > and early return first, and then check what vbt says, to reduce the > dmesg noise. > > I'll probably want to see a debug message if we're enabling aux > backlight even if dev_priv->vbt.backlight.type != > INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE. It's the kind of debug trace > you'll really want to get first. So I've gone ahead and pushed patches 1-3 and 5 in this series, as they were tested as part of the series I posted. BR, Jani. > > BR, > Jani. > > > >> + } >> >> panel->backlight.setup = intel_dp_aux_setup_backlight; >> panel->backlight.enable = intel_dp_aux_enable_backlight; -- Jani Nikula, Intel Open Source Graphics Center