[Intel-gfx] [PATCH v2 04/11] drm/i915/preempt: Default to disabled mid-command preemption levels

[Joonas Lahtinen]

On Wed, 2017-09-27 at 17:44 +0100, Chris Wilson wrote:
> From: Michał Winiarski <michal.winiarski at intel.com>
> 
> Supporting fine-granularity preemption levels may require changes in
> userspace batch buffer programming. Therefore, we need to fallback to
> safe default values, rather that use hardware defaults. Userspace is
> still able to enable fine-granularity, since we're whitelisting the
> register controlling it in WaEnablePreemptionGranularityControlByUMD.
> 
> Signed-off-by: Michał Winiarski <michal.winiarski at intel.com>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

<SNIP>

> +	/* Supporting preemption with fine-granularity requires changes in the
> +	 * batch buffer programming. Since we can't break old userspace, we
> +	 * need to set our default preemption level to safe value. Userspace is
> +	 * still able to use more fine-grained preemption levels, since in
> +	 * WaEnablePreemptionGranularityControlByUMD we're whitelisting the
> +	 * per-ctx register. As such, WaDisableMidCmdPreemption is not a real
> +	 * HW workaround, but merely a way to start using preemption while
> +	 * maintaining old contract with userspace.
> +	 */
> +
> +	/* WaDisable3DMidCmdPreemption:skl,bxt,glk,cfl */
> +	WA_CLR_BIT_MASKED(GEN8_CS_CHICKEN1, GEN9_PREEMPT_3D_OBJECT_LEVEL);
> +
> +	/* WaDisableGPGPUMidCmdPreemption:skl,bxt,blk,cfl */
> +	WA_SET_FIELD_MASKED(GEN8_CS_CHICKEN1, GEN9_PREEMPT_GPGPU_LEVEL_MASK,
> +			    GEN9_PREEMPT_GPGPU_COMMAND_LEVEL);

Lets avoid confusion by not inventing Wa names (It's not in the
database at least). This also applies to pretty much any new HW,
including CNL like the previous actual W/A.

Other than that, this is the correct thing to do so drop the false
name, and just leave this as a remark which references the other W/A.

Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation