From: Lyude Paul <lyude@redhat.com>
To: Jani Nikula <jani.nikula@intel.com>, intel-gfx@lists.freedesktop.org
Cc: David Airlie <airlied@linux.ie>,
linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
AceLan Kao <acelan.kao@canonical.com>,
Perry Yuan <pyuan@redhat.com>
Subject: Re: [Intel-gfx] [PATCH v3 4/5] drm/i915: Don't use VBT for detecting DPCD backlight controls
Date: Fri, 17 Jan 2020 15:24:13 -0500 [thread overview]
Message-ID: <05569e0b86c62589e67a9355159e9db8e42c0820.camel@redhat.com> (raw)
In-Reply-To: <87zhemgvrn.fsf@intel.com>
On Fri, 2020-01-17 at 13:36 +0200, Jani Nikula wrote:
> On Thu, 16 Jan 2020, Lyude Paul <lyude@redhat.com> 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 <lyude@redhat.com>
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112376
> > Cc: Jani Nikula <jani.nikula@intel.com>
> > Cc: Perry Yuan <pyuan@redhat.com>
> > Cc: AceLan Kao <acelan.kao@canonical.com>
> > ---
> > .../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.
Good point, I'll send a respin of this patch with those changes
>
> BR,
> Jani.
>
>
>
> > + }
> >
> > panel->backlight.setup = intel_dp_aux_setup_backlight;
> > panel->backlight.enable = intel_dp_aux_enable_backlight;
--
Cheers,
Lyude Paul
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next prev parent reply other threads:[~2020-01-17 20:24 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-16 21:16 [Intel-gfx] [PATCH v3 0/5] drm/i915: eDP DPCD aux backlight fixes Lyude Paul
2020-01-16 21:16 ` [Intel-gfx] [PATCH v3 1/5] drm/i915: Fix eDP DPCD aux max backlight calculations Lyude Paul
2020-01-16 21:16 ` [Intel-gfx] [PATCH v3 2/5] drm/i915: Assume 100% brightness when not in DPCD control mode Lyude Paul
2020-01-16 21:16 ` [Intel-gfx] [PATCH v3 3/5] drm/i915: Fix DPCD register order in intel_dp_aux_enable_backlight() Lyude Paul
2020-01-16 21:16 ` [Intel-gfx] [PATCH v3 4/5] drm/i915: Don't use VBT for detecting DPCD backlight controls Lyude Paul
2020-01-17 11:36 ` Jani Nikula
2020-01-17 11:47 ` Jani Nikula
2020-01-17 20:24 ` Lyude Paul [this message]
2020-01-17 23:21 ` [Intel-gfx] [PATCH v4] " Lyude Paul
2020-01-22 9:17 ` Jani Nikula
2020-01-16 21:16 ` [Intel-gfx] [PATCH v3 5/5] drm/i915: Auto detect DPCD backlight support by default Lyude Paul
2020-01-16 23:26 ` [Intel-gfx] ✓ Fi.CI.BAT: success for drm/i915: eDP DPCD aux backlight fixes (rev6) Patchwork
2020-01-16 23:26 ` [Intel-gfx] ✗ Fi.CI.BUILD: warning " Patchwork
2020-01-18 3:23 ` [Intel-gfx] ✓ Fi.CI.BAT: success for drm/i915: eDP DPCD aux backlight fixes (rev7) Patchwork
2020-01-18 3:23 ` [Intel-gfx] ✗ Fi.CI.BUILD: warning " Patchwork
2020-01-20 5:16 ` [Intel-gfx] ✓ Fi.CI.IGT: success for drm/i915: eDP DPCD aux backlight fixes (rev6) Patchwork
2020-01-20 19:55 ` [Intel-gfx] ✓ Fi.CI.IGT: success for drm/i915: eDP DPCD aux backlight fixes (rev7) Patchwork
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