[Intel-gfx] [PATCH v4 4/6] drm/i915/guc: (re)initialise doorbell h/w when enabling GuC submission

[Yu Dai]

On 04/07/2016 10:21 AM, Dave Gordon wrote:
> During a hibernate/resume cycle, the whole system is reset, including
> the GuC and the doorbell hardware. Then the system is booted up, drivers
> are loaded, etc -- the GuC firmware may be loaded and set running at this
> point. But then, the booted kernel is replaced by the hibernated image,
> and this resumed kernel will also try to reload the GuC firmware (which
> will fail). To recover, we reset the GuC and try again (which should
> work). But this GuC reset doesn't also reset the doorbell hardware, so
> it can be left in a state inconsistent with that assumed by the driver
> and the GuC.
>
> It would be better if the GuC reset also cleared all doorbell state,
> but that's not how the hardware currently works; also, the driver cannot
> directly reprogram the doorbell hardware (only the GuC can do that).
>
> So this patch cycles through all doorbells, assigning and releasing each
> in turn, so that all the doorbell hardware is left in a consistent state,
> no matter how it was programmed by the previously-running kernel and/or
> GuC firmware.
>
> This patch can be removed if/when the GuC firmware is updated so that it
> (re)initialises the doorbell hardware after every firmware (re)load.
>
> Signed-off-by: Dave Gordon <david.s.gordon at intel.com>
> ---
>   drivers/gpu/drm/i915/i915_guc_submission.c | 46 +++++++++++++++++++++++++++++-
>   1 file changed, 45 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
> index 2fc69f1..f466eab 100644
> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
> @@ -707,6 +707,50 @@ static void guc_client_free(struct drm_device *dev,
>   	kfree(client);
>   }
>   
> +/*
> + * Borrow the first client to set up & tear down every doorbell
> + * in turn, to ensure that all doorbell h/w is (re)initialised.
> + */
> +static void guc_init_doorbell_hw(struct intel_guc *guc)
> +{
> +	struct drm_i915_private *dev_priv = guc_to_i915(guc);
> +	struct i915_guc_client *client = guc->execbuf_client;
> +	struct guc_doorbell_info *doorbell;
> +	uint16_t db_id, i;
> +	void *base;
> +	int ret;
> +
> +	base = kmap_atomic(i915_gem_object_get_page(client->client_obj, 0));
> +	doorbell = base + client->doorbell_offset;
> +	db_id = client->doorbell_id;
> +
> +	for (i = 0; i < GUC_MAX_DOORBELLS; ++i) {
> +		i915_reg_t drbreg = GEN8_DRBREGL(i);
> +		u32 value = I915_READ(drbreg);
> +
> +		ret = guc_update_doorbell_id(client, doorbell, i);
> +
> +		if (((value & GUC_DOORBELL_ENABLED) && (i != db_id)) || ret)
> +			DRM_DEBUG_DRIVER("Doorbell reg 0x%x was 0x%x, ret %d\n",
> +				drbreg.reg, value, ret);
> +	}
> +
> +	/* Restore to original value */
> +	guc_update_doorbell_id(client, doorbell, db_id);
> +
> +	for (i = 0; i < GUC_MAX_DOORBELLS; ++i) {
> +		i915_reg_t drbreg = GEN8_DRBREGL(i);
> +		u32 value = I915_READ(drbreg);
> +
> +		if ((value & GUC_DOORBELL_ENABLED) && (i != db_id))
> +			DRM_DEBUG_DRIVER("Doorbell reg 0x%x finally 0x%x\n",
> +						drbreg.reg, value);
> +
> +	}
> +

The for loop above is not needed. It can be merged into previous loop by 
print out new drbreg value (read it again after update_doorbell_id).

At this point, only need to check if db_id is correctly enabled or not 
by print out I915_READ(GEN8_DRBREGL(db_id)).

Alex

> +	kunmap_atomic(base);
> +}
> +
>   /**
>    * guc_client_alloc() - Allocate an i915_guc_client
>    * @dev:	drm device
> @@ -971,8 +1015,8 @@ int i915_guc_submission_enable(struct drm_device *dev)
>   	}
>   
>   	guc->execbuf_client = client;
> -
>   	host2guc_sample_forcewake(guc, client);
> +	guc_init_doorbell_hw(guc);
>   
>   	return 0;
>   }