Re: [PATCH] drm/i915: fix for WaDisableDopClockGating:bdw

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Feb 08, 2017 at 06:10:31PM +0000, Robert Bragg wrote:
> This workaround for BDW was incomplete as it also requires EUTC clock
> gating to be disabled via UCGCTL1.

IIRC that matches what I told Ben years ago when the w/a was first
being added, and matches what I put in the CHV code when it still
had this w/a. Presumably it still holds for BDW.

> 
> Signed-off-by: Robert Bragg <robert@sixbynine.org>
> ---
>  drivers/gpu/drm/i915/intel_ringbuffer.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 49fa8006c6a2..fa1b400a79d0 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -776,6 +776,7 @@ static int bdw_init_workarounds(struct intel_engine_cs *engine)
>  	/* WaDisableDopClockGating:bdw */
>  	WA_SET_BIT_MASKED(GEN7_ROW_CHICKEN2,
>  			  DOP_CLOCK_GATING_DISABLE);
> +	WA_SET_BIT(GEN6_UCGCTL1, GEN6_EU_TCUNIT_CLOCK_GATE_DISABLE);

The UCGCTL registers aren't clobbered by GPU resets and whatnot, so
we've historically kept them in the init_clock_gating() side.

Also it's not a masked register, and I'm not sure not all the bits
default to 0, so you shouldn't perhaps just clobber them. Sadly the
spec seems to have gone mad and no longer shows the default values
for registers so I can't double check right now.

>  
>  	WA_SET_BIT_MASKED(HALF_SLICE_CHICKEN3,
>  			  GEN8_SAMPLER_POWER_BYPASS_DIS);
> -- 
> 2.11.0
> 
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-- 
Ville Syrjälä
Intel OTC
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