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Commit 59db36cf authored by Michał Winiarski's avatar Michał Winiarski Committed by Chris Wilson
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drm/i915/guc: Simplify GuC doorbell logic 



All we're really doing is incrementing a simple counter in a
doorbell_info struct. We can do without extra variables and a separate
counter kept in guc_client. Since it's gone, we're also removing its
debugfs.
The only functional change here, is that we're no longer treating 0 as a
special value. GuC doesn't seem to care, why should we?

v2: Restore desc->tail update.
v3: Drop the retry loop, assert that doorbell cookie doesn't change
behind our back.
v4: WARN rather than BUG, use xchg. (Chris)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Suggested-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: default avatarMichał Winiarski <michal.winiarski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170914105125.3031-1-michal.winiarski@intel.com


Reviewed-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
parent 85e2fe67

drivers/gpu/drm/i915/i915_debugfs.c

+2 −2
Original line number Diff line number Diff line
@@ -2445,8 +2445,8 @@ static void i915_guc_client_info(struct seq_file *m, 


	seq_printf(m, "\tPriority %d, GuC stage index: %u, PD offset 0x%x\n",

		client->priority, client->stage_id, client->proc_desc_offset);

	seq_printf(m, "\tDoorbell id %d, offset: 0x%lx, cookie 0x%x\n",

		client->doorbell_id, client->doorbell_offset, client->doorbell_cookie);

	seq_printf(m, "\tDoorbell id %d, offset: 0x%lx\n",

		client->doorbell_id, client->doorbell_offset);

	seq_printf(m, "\tWQ size %d, offset: 0x%x, tail %d\n",

		client->wq_size, client->wq_offset, client->wq_tail);

drivers/gpu/drm/i915/i915_guc_submission.c

+13 −47
Original line number Diff line number Diff line
@@ -192,13 +192,12 @@ static int __create_doorbell(struct i915_guc_client *client) 


	doorbell = __get_doorbell(client);

	doorbell->db_status = GUC_DOORBELL_ENABLED;

	doorbell->cookie = client->doorbell_cookie;

	doorbell->cookie = 0;



	err = __guc_allocate_doorbell(client->guc, client->stage_id);

	if (err) {

	if (err)

		doorbell->db_status = GUC_DOORBELL_DISABLED;

		doorbell->cookie = 0;

	}



	return err;

}
@@ -466,57 +465,24 @@ static void guc_reset_wq(struct i915_guc_client *client) 
	client->wq_tail = 0;

}



static int guc_ring_doorbell(struct i915_guc_client *client)

static void guc_ring_doorbell(struct i915_guc_client *client)

{

	struct guc_process_desc *desc = __get_process_desc(client);

	union guc_doorbell_qw db_cmp, db_exc, db_ret;

	union guc_doorbell_qw *db;

	int attempt = 2, ret = -EAGAIN;

	struct guc_doorbell_info *db;

	u32 cookie;



	/* Update the tail so it is visible to GuC */

	desc->tail = client->wq_tail;



	/* current cookie */

	db_cmp.db_status = GUC_DOORBELL_ENABLED;

	db_cmp.cookie = client->doorbell_cookie;



	/* cookie to be updated */

	db_exc.db_status = GUC_DOORBELL_ENABLED;

	db_exc.cookie = client->doorbell_cookie + 1;

	if (db_exc.cookie == 0)

		db_exc.cookie = 1;



	/* pointer of current doorbell cacheline */

	db = (union guc_doorbell_qw *)__get_doorbell(client);

	db = __get_doorbell(client);



	while (attempt--) {

		/* lets ring the doorbell */

		db_ret.value_qw = atomic64_cmpxchg((atomic64_t *)db,

			db_cmp.value_qw, db_exc.value_qw);



		/* if the exchange was successfully executed */

		if (db_ret.value_qw == db_cmp.value_qw) {

			/* db was successfully rung */

			client->doorbell_cookie = db_exc.cookie;

			ret = 0;

			break;

		}

	/* we're not expecting the doorbell cookie to change behind our back */

	cookie = READ_ONCE(db->cookie);

	WARN_ON_ONCE(xchg(&db->cookie, cookie + 1) != cookie);



	/* XXX: doorbell was lost and need to acquire it again */

		if (db_ret.db_status == GUC_DOORBELL_DISABLED)

			break;



		DRM_WARN("Cookie mismatch. Expected %d, found %d\n",

			 db_cmp.cookie, db_ret.cookie);



		/* update the cookie to newly read cookie from GuC */

		db_cmp.cookie = db_ret.cookie;

		db_exc.cookie = db_ret.cookie + 1;

		if (db_exc.cookie == 0)

			db_exc.cookie = 1;

	}



	return ret;

	GEM_BUG_ON(db->db_status != GUC_DOORBELL_ENABLED);

}



/**
@@ -549,7 +515,7 @@ static void i915_guc_submit(struct intel_engine_cs *engine) 
			spin_lock(&client->wq_lock);



			guc_wq_item_append(client, rq);

			WARN_ON(guc_ring_doorbell(client));

			guc_ring_doorbell(client);



			client->submissions[engine_id] += 1;

drivers/gpu/drm/i915/intel_uc.h

+0 −1
Original line number Diff line number Diff line
@@ -66,7 +66,6 @@ struct i915_guc_client { 


	u16 doorbell_id;

	unsigned long doorbell_offset;

	u32 doorbell_cookie;



	spinlock_t wq_lock;

	uint32_t wq_offset;