Re: [08/11] drm/i915/guc: Wait for doorbell to be inactive before deallocating

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On pe, 2017-03-10 at 08:28 -0800, Oscar Mateo wrote:
> Doorbell release flow requires that we wait for GEN8_DRB_VALID bit to go
> to zero after updating db_status before we call the GuC to release the
> doorbell.
> 
> Kudos to Daniele for finding this out.
> 
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
> Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>

<SNIP>
 
>  static int __destroy_doorbell(struct i915_guc_client *client)
>  {
> +	struct drm_i915_private *dev_priv = guc_to_i915(client->guc);
>  	struct guc_doorbell_info *doorbell;
> +	u16 db_id = client->doorbell_id;
> +
> +	GEM_BUG_ON(db_id >= GUC_DOORBELL_INVALID);
>  
>  	doorbell = __get_doorbell(client);
>  	doorbell->db_status = GUC_DOORBELL_DISABLED;
>  	doorbell->cookie = 0;
>  
> +	/* Doorbell release flow requires that we wait for GEN8_DRB_VALID bit
> +	 * to go to zero after updating db_status before we call the GuC to
> +	 * release the doorbell */
> +	if (wait_for_us(!(I915_READ(GEN8_DRBREGL(db_id)) & GEN8_DRB_VALID), 10))
> +		DRM_ERROR("Doorbell never became invalid after disable\n");

Would the appropriate action be to return -ETIMEOUT and not proceed
with deallocation? I would at least WARN here. If GuC submission gets
enabled, we should yell if it's not working. So only the enable stage
should bail out with DRM_ERRORs and without WARN.

> +
>  	return __guc_deallocate_doorbell(client->guc, client->ctx_index);
>  }

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