Re: [PATCH V2] drm/i915: Use I915_MAP_WC for execlists context buffer on the platforms without LLC

["Zhao, Yakui" <yakui.zhao@intel.com>]

>-----Original Message-----
>From: Chris Wilson [mailto:chris@chris-wilson.co.uk]
>Sent: Friday, June 22, 2018 2:36 PM
>To: Zhao, Yakui <yakui.zhao@intel.com>; intel-gfx@lists.freedesktop.org
>Cc: Zhao, Yakui <yakui.zhao@intel.com>
>Subject: Re: [PATCH V2] drm/i915: Use I915_MAP_WC for execlists context
>buffer on the platforms without LLC
>
>Quoting Zhao Yakui (2018-06-22 07:09:10)
>> @@ -2728,6 +2729,7 @@ populate_lr_context(struct i915_gem_context *ctx,
>>                     struct intel_engine_cs *engine,
>>                     struct intel_ring *ring)  {
>> +       enum i915_map_type map = HAS_LLC(ctx->i915) ? I915_MAP_WB :
>> + I915_MAP_WC;
>>         void *vaddr;
>>         u32 *regs;
>>         int ret;
>> @@ -2738,13 +2740,12 @@ populate_lr_context(struct i915_gem_context
>*ctx,
>>                 return ret;
>>         }
>>
>> -       vaddr = i915_gem_object_pin_map(ctx_obj, I915_MAP_WB);
>> +       vaddr = i915_gem_object_pin_map(ctx_obj, map);
>
>As this uses the cpu domain and flushed afterwards, this one is correct in its
>usage of MAP_WB.

In this function the content of context state is flushed.

But the function of execlists_submit_ports will update it again before writing the ELSP port.
And there is no flush. In fact after the ELSP port is written, the HW will start to execute the submitted commands.


>-Chris
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