Re: [PATCH v3 4/6] drm/i915/gen8: Add WaFlushCoherentL3CacheLinesAtContextSwitch workaround

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On 05/06/2015 15:48, Ville Syrjälä wrote:
On Fri, Jun 05, 2015 at 02:56:48PM +0100, Arun Siluvery wrote:
In Indirect context w/a batch buffer,
+WaFlushCoherentL3CacheLinesAtContextSwitch

Signed-off-by: Rafael Barbalho <rafael.barbalho@xxxxxxxxx>
Signed-off-by: Arun Siluvery <arun.siluvery@xxxxxxxxxxxxxxx>
---
  drivers/gpu/drm/i915/i915_reg.h  | 1 +
  drivers/gpu/drm/i915/intel_lrc.c | 8 ++++++++
  2 files changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 84af255..5203c79 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -426,6 +426,7 @@
  #define   PIPE_CONTROL_INDIRECT_STATE_DISABLE		(1<<9)
  #define   PIPE_CONTROL_NOTIFY				(1<<8)
  #define   PIPE_CONTROL_FLUSH_ENABLE			(1<<7) /* gen7+ */
+#define   PIPE_CONTROL_DC_FLUSH_ENABLE			(1<<5)
  #define   PIPE_CONTROL_VF_CACHE_INVALIDATE		(1<<4)
  #define   PIPE_CONTROL_CONST_CACHE_INVALIDATE		(1<<3)
  #define   PIPE_CONTROL_STATE_CACHE_INVALIDATE		(1<<2)
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index a71eb81..9d8cf65c 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1101,6 +1101,14 @@ static int gen8_init_indirectctx_bb(struct intel_engine_cs *ring)
  	/* WaDisableCtxRestoreArbitration:bdw,chv */
  	cmd[index++] = MI_ARB_ON_OFF | MI_ARB_DISABLE;

+	/* WaFlushCoherentL3CacheLinesAtContextSwitch:bdw,chv */
+	cmd[index++] = GFX_OP_PIPE_CONTROL(6);
+	cmd[index++] = PIPE_CONTROL_DC_FLUSH_ENABLE;
+	cmd[index++] = 0;
+	cmd[index++] = 0;
+	cmd[index++] = 0;
+	cmd[index++] = 0;
+

This looks incomplete. Seems like you should have LRIs around this
guy to enable/disable the L3SQCREG4 coherent line flush bit.

And chv shouldn't do coherent L3, so this might not be needed there.


I checked with HW team and yes I need to add LRIs to enable/disable L3SQCREG4 coherent line flush bit.
As you mentioned, it is not required for CHV.

Also do we need a CS stall here too?
"DC Flush Enable 5 Requires stall bit ([20] of DW) set for all GPGPU and Media Workloads."

I didn't check the restrictions of this bit, will check again and correc this.

regards
Arun

Supposedly we should add the DC flush to the normal ring flush hooks
too. But that's a separate issue.

  	/* padding */
          while (index < end)
  		cmd[index++] = MI_NOOP;
--
2.3.0

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