Re: [PATCH v2 12/22] drm/i915: Preserve SSC earlier

Jani Nikula
2015-09-01T06:46:37Z

On Mon, 31 Aug 2015, Jesse Barnes <jbarnes@virtuousgeek.org> wrote:
> On 07/15/2015 04:57 AM, Lukas Wunner wrote:
>> Commit 92122789b2d6 ("drm/i915: preserve SSC if previously set v3")
>> added code to intel_modeset_gem_init to override the SSC status read
>> from VBT with the SSC status set by BIOS.
>>
>> However, intel_modeset_gem_init is invoked *after* intel_modeset_init,
>> which calls intel_setup_outputs, which *modifies* SSC status by way of
>> intel_init_pch_refclk. So unlike advertised, intel_modeset_gem_init
>> doesn't preserve the SSC status set by BIOS but whatever
>> intel_init_pch_refclk decided on.
>>
>> This is a problem on dual gpu laptops such as the MacBook Pro which
>> require either a handler to switch DDC lines, or the discrete gpu
>> to proxy DDC/AUX communication: Both the handler and the discrete
>> gpu may initialize after the i915 driver, and consequently, an LVDS
>> connector may initially seem disconnected and the SSC therefore
>> is disabled by intel_init_pch_refclk, but on reprobe the connector
>> may turn out to be connected and the SSC must then be enabled.
>>
>> Due to 92122789b2d6 however, the SSC is not enabled on reprobe since
>> it is assumed BIOS disabled it while in fact it was disabled by
>> intel_init_pch_refclk.
>>
>> Also, because the SSC status is preserved so late, the preserved value
>> only ever gets used on resume but not on panel initialization:
>> intel_modeset_init calls intel_init_display which indirectly calls
>> intel_panel_use_ssc via multiple subroutines, *before* the BIOS value
>> overrides the VBT value in intel_modeset_gem_init (intel_panel_use_ssc
>> is the sole user of dev_priv->vbt.lvds_use_ssc).
>>
>> Fix this by moving the code introduced by 92122789b2d6 from
>> intel_modeset_gem_init to intel_modeset_init before the invocation
>> of intel_setup_outputs and intel_init_display.
>>
>> Add a DRM_DEBUG_KMS as suggested way back by Jani:
>> http://lists.freedesktop.org/archives/intel-gfx/2014-June/046666.html
>>
>> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=88861
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115
>> Tested-by: Paul Hordiienko <pvt.gord@gmail.com>
>> [MBP 6,2 2010 intel ILK + nvidia GT216 pre-retina]
>> Tested-by: William Brown <william@blackhats.net.au>
>> [MBP 8,2 2011 intel SNB + amd turks pre-retina]
>> Tested-by: Lukas Wunner <lukas@wunner.de>
>> [MBP 9,1 2012 intel IVB + nvidia GK107 pre-retina]
>> Tested-by: Bruno Bierbaumer <bruno@bierbaumer.net>
>> [MBP 11,3 2013 intel HSW + nvidia GK107 retina -- work in progress]
>>
>> Fixes: 92122789b2d6 ("drm/i915: preserve SSC if previously set v3")
>> Signed-off-by: Lukas Wunner <lukas@wunner.de>
>> ---
>> drivers/gpu/drm/i915/intel_display.c | 29 ++++++++++++++++++-----------
>> 1 file changed, 18 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
>> index af0bcfe..6335883 100644
>> --- a/drivers/gpu/drm/i915/intel_display.c
>> +++ b/drivers/gpu/drm/i915/intel_display.c
>> @@ -14893,6 +14893,24 @@ void intel_modeset_init(struct drm_device *dev)
>> if (INTEL_INFO(dev)->num_pipes == 0)
>> return;
>>
>> + /*
>> + * There may be no VBT; and if the BIOS enabled SSC we can
>> + * just keep using it to avoid unnecessary flicker. Whereas if the
>> + * BIOS isn't using it, don't assume it will work even if the VBT
>> + * indicates as much.
>> + */
>> + if (HAS_PCH_IBX(dev) || HAS_PCH_CPT(dev)) {
>> + bool bios_lvds_use_ssc = !!(I915_READ(PCH_DREF_CONTROL) &
>> + DREF_SSC1_ENABLE);
>> +
>> + if (dev_priv->vbt.lvds_use_ssc != bios_lvds_use_ssc) {
>> + DRM_DEBUG_KMS("SSC %sabled by BIOS, overriding VBT which says %sabled\n",
>> + bios_lvds_use_ssc ? "en" : "dis",
>> + dev_priv->vbt.lvds_use_ssc ? "en" : "dis");
>> + dev_priv->vbt.lvds_use_ssc = bios_lvds_use_ssc;
>> + }
>> + }
>> +
>> intel_init_display(dev);
>> intel_init_audio(dev);
>>
>> @@ -15446,7 +15464,6 @@ err:
>>
>> void intel_modeset_gem_init(struct drm_device *dev)
>> {
>> - struct drm_i915_private *dev_priv = dev->dev_private;
>> struct drm_crtc *c;
>> struct drm_i915_gem_object *obj;
>> int ret;
>> @@ -15455,16 +15472,6 @@ void intel_modeset_gem_init(struct drm_device *dev)
>> intel_init_gt_powersave(dev);
>> mutex_unlock(&dev->struct_mutex);
>>
>> - /*
>> - * There may be no VBT; and if the BIOS enabled SSC we can
>> - * just keep using it to avoid unnecessary flicker. Whereas if the
>> - * BIOS isn't using it, don't assume it will work even if the VBT
>> - * indicates as much.
>> - */
>> - if (HAS_PCH_IBX(dev) || HAS_PCH_CPT(dev))
>> - dev_priv->vbt.lvds_use_ssc = !!(I915_READ(PCH_DREF_CONTROL) &
>> - DREF_SSC1_ENABLE);
>> -
>> intel_modeset_init_hw(dev);
>>
>> intel_setup_overlay(dev);
>>
>
> Yeah looks good (and I'm having deja vu here; I thought I ran into the same ordering issue at one point in a report from krh, but I guess I never fixed it; didn't have test hw at the time).
>
> Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>

Pushed this one patch to drm-intel-next-fixes, thanks for the patch and
review.

BR,
Jani.

>
> Thanks,
> Jesse
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

--
Jani Nikula, Intel Open Source Technology Center