Re: [PATCH 05/12] drm/i915/bxt: update WaSetHDCunitClckGatingDisable

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

On Fri, Sep 25, 2015 at 02:33:39PM +0100, Arun Siluvery wrote:
> The implementation for this WA is same as WaSetHdcUnitClockGatingDisableInUcgctl6.
> Both of them are for BXT:A0 except that WaSetHdcUnitClockGatingDisableInUcgctl6
> is applicable only when either SS0 or SS2 is active but if we apply the former WA
> then the latter one also gets applied irrespective of which SS is enabled.
> 
> Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 093a5e4..c73d37d 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -124,12 +124,17 @@ static void bxt_init_clock_gating(struct drm_device *dev)
>  	I915_WRITE(GEN8_UCGCTL6, I915_READ(GEN8_UCGCTL6) |
>  		   GEN8_SDEUNIT_CLOCK_GATE_DISABLE);
>  
> -	/*
> -	 * FIXME:
> -	 * GEN8_HDCUNIT_CLOCK_GATE_DISABLE_HDCREQ applies on 3x6 GT SKUs only.
> +	/* WaSetHDCunitClckGatingDisable:bxt */
> +	/* WaSetHdcUnitClockGatingDisableInUcgctl6:bxt */
> +	/* The implementation is same for both of these WA except that
> +	 * WaSetHdcUnitClockGatingDisableInUcgctl6 is only applicable when
> +	 * either SS0 or SS2 is active but if we apply the first one then the
> +	 * second one also gets applied irrespective of which SS is enabled.
>  	 */
> -	I915_WRITE(GEN8_UCGCTL6, I915_READ(GEN8_UCGCTL6) |
> -		   GEN8_HDCUNIT_CLOCK_GATE_DISABLE_HDCREQ);
> +	if (INTEL_REVID(dev) == BXT_REVID_A0) {
> +		I915_WRITE(GEN8_UCGCTL6, (I915_READ(GEN8_UCGCTL6) |
> +					  GEN8_HDCUNIT_CLOCK_GATE_DISABLE_HDCREQ));
> +	}

Again BSpec seems confused. It says this applies to BXT from A0, and SKL
from C0. The register description only says to do it for 3x6 BXT, and
w/a db says both workarounds are for BXT until A0. Quite a nice mess.

>  
>  	if (INTEL_REVID(dev) == BXT_REVID_A0) {
>  		/*
> -- 
> 1.9.1
> 
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-- 
Ville Syrjälä
Intel OTC
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