Re: [PATCH 3/4] drm/i915/guc: refactor doorbell management code

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 08/06/16 11:55, Dave Gordon wrote:
> During a hibernate/resume cycle, the driver, the GuC, and the doorbell
> hardware can end up in inconsistent states. This patch refactors the
> driver's handling and tracking of doorbells, in preparation for a later
> one which will resolve the issue.

Perhaps a few word on the goal, method and result of refactoring. Would 
be good for documentation and easier review.

> Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_guc_submission.c | 87 ++++++++++++++++++------------
>   1 file changed, 53 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
> index 7510841..eef67c8 100644
> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
> @@ -174,36 +174,63 @@ static int host2guc_sample_forcewake(struct intel_guc *guc,
>    * client object which contains the page being used for the doorbell
>    */
>
> -static void guc_init_doorbell(struct intel_guc *guc,
> -			      struct i915_guc_client *client)
> +static int guc_update_doorbell_id(struct i915_guc_client *client,
> +				  struct guc_doorbell_info *doorbell,
> +				  u16 new_id)
>   {
> -	struct guc_doorbell_info *doorbell;
> +	struct sg_table *sg = client->guc->ctx_pool_obj->pages;
> +	void *doorbell_bitmap = client->guc->doorbell_bitmap;
> +	struct guc_context_desc desc;
> +	size_t len;
> +
> +	if (client->doorbell_id != GUC_INVALID_DOORBELL_ID &&
> +	    test_bit(client->doorbell_id, doorbell_bitmap)) {
> +		/* Deactivate the old doorbell */
> +		doorbell->db_status = GUC_DOORBELL_DISABLED;
> +		(void)host2guc_release_doorbell(client->guc, client);
> +		clear_bit(client->doorbell_id, doorbell_bitmap);
> +	}
>
> -	doorbell = client->client_base + client->doorbell_offset;
> +	/* Update the GuC's idea of the doorbell ID */
> +	len = sg_pcopy_to_buffer(sg->sgl, sg->nents, &desc, sizeof(desc),
> +			     sizeof(desc) * client->ctx_index);
> +	if (len != sizeof(desc))
> +		return -EFAULT;
> +	desc.db_id = new_id;
> +	len = sg_pcopy_from_buffer(sg->sgl, sg->nents, &desc, sizeof(desc),
> +			     sizeof(desc) * client->ctx_index);
> +	if (len != sizeof(desc))
> +		return -EFAULT;
> +
> +	client->doorbell_id = new_id;
> +	if (new_id == GUC_INVALID_DOORBELL_ID)
> +		return 0;
>
> +	/* Activate the new doorbell */
> +	set_bit(client->doorbell_id, doorbell_bitmap);
>   	doorbell->db_status = GUC_DOORBELL_ENABLED;
>   	doorbell->cookie = 0;
> +	return host2guc_allocate_doorbell(client->guc, client);

A bunch of new code here which wasn't done on doorbell init before. 
Populating the ctx_pool_obj and hust2guc call. I think the commit needs 
to explain what is happening here.

Maybe it is mostly a matter of copying over some text from the cover 
letter, but ideally it should explain what it is doing more precisely.

>   }
>
> -static void guc_disable_doorbell(struct intel_guc *guc,
> -				 struct i915_guc_client *client)
> +static void guc_init_doorbell(struct intel_guc *guc,
> +			      struct i915_guc_client *client,
> +			      uint16_t db_id)
>   {
> -	struct drm_i915_private *dev_priv = guc_to_i915(guc);
>   	struct guc_doorbell_info *doorbell;
> -	i915_reg_t drbreg = GEN8_DRBREGL(client->doorbell_id);
> -	int value;
>
>   	doorbell = client->client_base + client->doorbell_offset;
>
> -	doorbell->db_status = GUC_DOORBELL_DISABLED;
> -
> -	I915_WRITE(drbreg, I915_READ(drbreg) & ~GEN8_DRB_VALID);
> +	guc_update_doorbell_id(client, doorbell, db_id);
> +}

This function does not end up doing anything now, just a pass-through to 
guc_update_doorbell_id.

What happens to the write to drbreg ? It is completely gone and also 
from the init doorbell path together with the write to another register.

>
> -	value = I915_READ(drbreg);
> -	WARN_ON((value & GEN8_DRB_VALID) != 0);
> +static void guc_disable_doorbell(struct intel_guc *guc,
> +				 struct i915_guc_client *client)
> +{
> +	struct guc_doorbell_info *doorbell;
>
> -	I915_WRITE(GEN8_DRBREGU(client->doorbell_id), 0);
> -	I915_WRITE(drbreg, 0);
> +	doorbell = client->client_base + client->doorbell_offset;
> +	guc_update_doorbell_id(client, doorbell, GUC_INVALID_DOORBELL_ID);
>
>   	/* XXX: wait for any interrupts */
>   	/* XXX: wait for workqueue to drain */
> @@ -251,7 +278,7 @@ static uint16_t assign_doorbell(struct intel_guc *guc, uint32_t priority)
>   	if (id == end)
>   		id = GUC_INVALID_DOORBELL_ID;
>   	else
> -		bitmap_set(guc->doorbell_bitmap, id, 1);
> +		set_bit(id, guc->doorbell_bitmap);

set_bit is atomic - is there a reason it is required here?

Actually the same question for the clear_bit above, where it was 
bitmap_clear before.

>
>   	DRM_DEBUG_DRIVER("assigned %s priority doorbell id 0x%x\n",
>   			hi_pri ? "high" : "normal", id);
> @@ -259,11 +286,6 @@ static uint16_t assign_doorbell(struct intel_guc *guc, uint32_t priority)
>   	return id;
>   }
>
> -static void release_doorbell(struct intel_guc *guc, uint16_t id)
> -{
> -	bitmap_clear(guc->doorbell_bitmap, id, 1);
> -}
> -
>   /*
>    * Initialise the process descriptor shared with the GuC firmware.
>    */
> @@ -657,8 +679,6 @@ static void guc_client_free(struct drm_device *dev,
>   	 */
>
>   	if (client->client_base) {
> -		uint16_t db_id = client->doorbell_id;
> -
>   		/*
>   		 * If we got as far as setting up a doorbell, make sure
>   		 * we shut it down before unmapping & deallocating the
> @@ -666,12 +686,8 @@ static void guc_client_free(struct drm_device *dev,
>   		 * GuC that we've finished with it, finally deallocate
>   		 * it in our bitmap
>   		 */
> -		if (db_id != GUC_INVALID_DOORBELL_ID) {
> +		if (client->doorbell_id != GUC_INVALID_DOORBELL_ID)
>   			guc_disable_doorbell(guc, client);
> -			if (test_bit(db_id, guc->doorbell_bitmap))
> -				host2guc_release_doorbell(guc, client);
> -			release_doorbell(guc, db_id);
> -		}
>
>   		kunmap(kmap_to_page(client->client_base));
>   	}
> @@ -706,6 +722,7 @@ static struct i915_guc_client *guc_client_alloc(struct drm_device *dev,
>   	struct drm_i915_private *dev_priv = dev->dev_private;
>   	struct intel_guc *guc = &dev_priv->guc;
>   	struct drm_i915_gem_object *obj;
> +	uint16_t db_id;
>
>   	client = kzalloc(sizeof(*client), GFP_KERNEL);
>   	if (!client)
> @@ -746,22 +763,24 @@ static struct i915_guc_client *guc_client_alloc(struct drm_device *dev,
>   	else
>   		client->proc_desc_offset = (GUC_DB_SIZE / 2);
>
> -	client->doorbell_id = assign_doorbell(guc, client->priority);
> -	if (client->doorbell_id == GUC_INVALID_DOORBELL_ID)
> +	db_id = assign_doorbell(guc, client->priority);
> +	if (db_id == GUC_INVALID_DOORBELL_ID)
>   		/* XXX: evict a doorbell instead */
>   		goto err;
>
>   	guc_init_proc_desc(guc, client);
>   	guc_init_ctx_desc(guc, client);
> -	guc_init_doorbell(guc, client);
> +	guc_init_doorbell(guc, client, db_id);
>
>   	/* XXX: Any cache flushes needed? General domain mgmt calls? */
>
>   	if (host2guc_allocate_doorbell(guc, client))
>   		goto err;
>
> -	DRM_DEBUG_DRIVER("new priority %u client %p: ctx_index %u db_id %u\n",
> -		priority, client, client->ctx_index, client->doorbell_id);
> +	DRM_DEBUG_DRIVER("new priority %u client %p: ctx_index %u\n",
> +		priority, client, client->ctx_index);
> +	DRM_DEBUG_DRIVER("doorbell id %u, cacheline offset 0x%x\n",
> +		client->doorbell_id, client->doorbell_offset);
>
>   	return client;
>
>

Regards,

Tvrtko
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