Re: [PATCH] drm/i915/fbc: Disable fbc with VT-d also with kbl and cfl

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Ville Syrjälä <ville.syrjala@linux.intel.com> writes:

> On Tue, Sep 25, 2018 at 04:38:03PM +0300, Mika Kuoppala wrote:
>> Using fbc with VT-d flickers also on kbl and cfl.
>> 
>> Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> Cc: Chris Wilson <chris@chris-wilson.co.uk>
>> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
>> Cc: <stable@vger.kernel.org> # v4.9+
>> Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
>> ---
>>  drivers/gpu/drm/i915/intel_fbc.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
>> index 74d425c700ef..a149f08c1b79 100644
>> --- a/drivers/gpu/drm/i915/intel_fbc.c
>> +++ b/drivers/gpu/drm/i915/intel_fbc.c
>> @@ -1275,9 +1275,10 @@ static int intel_sanitize_fbc_option(struct drm_i915_private *dev_priv)
>>  
>>  static bool need_fbc_vtd_wa(struct drm_i915_private *dev_priv)
>>  {
>> -	/* WaFbcTurnOffFbcWhenHyperVisorIsUsed:skl,bxt */
>> +	/* WaFbcTurnOffFbcWhenHyperVisorIsUsed:skl,bxt,kbl,cfl */
>
> The hsds seem to be saying that this was fixed in kbl/cnl. I guess the
> flicker could be due to a different vt-d vs. fbc issue.
>

I was trusting the wa database on this one.

> Is the chicken bit in CHICKEN_PIPESL in the correct position?

Yes it is zero.

>
> Hmm. Bspec doesn't list chicken bit for glk. That would seem to suggest
> that we need this w/a for glk as well.

Agreed. The questio is that should we follow bspec and logic or
leave it until we get a report if it is a problem?

cfl is close enough|similar in this respect that we mimic
kbl with it?

Thanks,
-Mika

>
>>  	if (intel_vtd_active() &&
>> -	    (IS_SKYLAKE(dev_priv) || IS_BROXTON(dev_priv))) {
>> +	    (IS_SKYLAKE(dev_priv) || IS_BROXTON(dev_priv) ||
>> +	     IS_KABYLAKE(dev_priv) || IS_COFFEELAKE(dev_priv))) {
>>  		DRM_INFO("Disabling framebuffer compression (FBC) to prevent screen flicker with VT-d enabled\n");
>>  		return true;
>>  	}
>> -- 
>> 2.17.1
>
> -- 
> Ville Syrjälä
> Intel