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

[Jani Nikula <jani.nikula@linux.intel.com>]

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
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> Intel-gfx@lists.freedesktop.org
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-- 
Jani Nikula, Intel Open Source Technology Center
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