[CI v4 2/3] drm/i915/guc: Introduce buffer based cmd transport

[Michal Wajdeczko <michal.wajdeczko@intel.com>]

Buffer based command transport can replace MMIO based mechanism.
It may be used to perform host-2-guc and guc-to-host communication.

Portions of this patch are based on work by:
 Michel Thierry <michel.thierry@intel.com>
 Robert Beckett <robert.beckett@intel.com>
 Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>

v2: use gem_object_pin_map (Chris)
    don't use DEBUG_RATELIMITED (Chris)
    don't track action stats (Chris)
    simplify next fence (Chris)
    use READ_ONCE (Chris)
    move blob allocation to new function (Chris)

v3: use static owner id (Daniele)
v4: but keep channel initialization generic (Daniele)
    and introduce owner_sub_id (Daniele)

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
---
 drivers/gpu/drm/i915/Makefile         |   1 +
 drivers/gpu/drm/i915/i915_drv.h       |   2 +
 drivers/gpu/drm/i915/intel_guc_ct.c   | 461 ++++++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_guc_ct.h   |  86 +++++++
 drivers/gpu/drm/i915/intel_guc_fwif.h |  43 ++++
 drivers/gpu/drm/i915/intel_uc.c       |  19 +-
 drivers/gpu/drm/i915/intel_uc.h       |   3 +-
 7 files changed, 613 insertions(+), 2 deletions(-)
 create mode 100644 drivers/gpu/drm/i915/intel_guc_ct.c
 create mode 100644 drivers/gpu/drm/i915/intel_guc_ct.h

diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index 7b05fb8..16dccf5 100644
--- a/drivers/gpu/drm/i915/Makefile
+++ b/drivers/gpu/drm/i915/Makefile
@@ -58,6 +58,7 @@ i915-y += i915_cmd_parser.o \
 
 # general-purpose microcontroller (GuC) support
 i915-y += intel_uc.o \
+	  intel_guc_ct.o \
 	  intel_guc_log.o \
 	  intel_guc_loader.o \
 	  intel_huc.o \
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 9ba2242..d2a5749 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -760,6 +760,7 @@ struct intel_csr {
 	func(has_gmbus_irq); \
 	func(has_gmch_display); \
 	func(has_guc); \
+	func(has_guc_ct); \
 	func(has_hotplug); \
 	func(has_l3_dpf); \
 	func(has_llc); \
@@ -2947,6 +2948,7 @@ intel_info(const struct drm_i915_private *dev_priv)
  * properties, so we have separate macros to test them.
  */
 #define HAS_GUC(dev_priv)	((dev_priv)->info.has_guc)
+#define HAS_GUC_CT(dev_priv)	((dev_priv)->info.has_guc_ct)
 #define HAS_GUC_UCODE(dev_priv)	(HAS_GUC(dev_priv))
 #define HAS_GUC_SCHED(dev_priv)	(HAS_GUC(dev_priv))
 #define HAS_HUC_UCODE(dev_priv)	(HAS_GUC(dev_priv))
diff --git a/drivers/gpu/drm/i915/intel_guc_ct.c b/drivers/gpu/drm/i915/intel_guc_ct.c
new file mode 100644
index 0000000..c4cbec1
--- /dev/null
+++ b/drivers/gpu/drm/i915/intel_guc_ct.c
@@ -0,0 +1,461 @@
+/*
+ * Copyright © 2016-2017 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include "i915_drv.h"
+#include "intel_guc_ct.h"
+
+enum { CTB_SEND = 0, CTB_RECV = 1 };
+
+enum { CTB_OWNER_HOST = 0 };
+
+void intel_guc_ct_init_early(struct intel_guc_ct *ct)
+{
+	/* we're using static channel owners */
+	ct->host_channel.owner = CTB_OWNER_HOST;
+}
+
+static inline const char *guc_ct_buffer_type_to_str(u32 type)
+{
+	switch (type) {
+	case INTEL_GUC_CT_BUFFER_TYPE_SEND:
+		return "SEND";
+	case INTEL_GUC_CT_BUFFER_TYPE_RECV:
+		return "RECV";
+	default:
+		return "<invalid>";
+	}
+}
+
+static void guc_ct_buffer_desc_init(struct guc_ct_buffer_desc *desc,
+				    u32 cmds_addr, u32 size, u32 owner)
+{
+	DRM_DEBUG_DRIVER("CT: desc %p init addr=%#x size=%u owner=%u\n",
+			 desc, cmds_addr, size, owner);
+	memset(desc, 0, sizeof(*desc));
+	desc->addr = cmds_addr;
+	desc->size = size;
+	desc->owner = owner;
+}
+
+static void guc_ct_buffer_desc_reset(struct guc_ct_buffer_desc *desc)
+{
+	DRM_DEBUG_DRIVER("CT: desc %p reset head=%u tail=%u\n",
+			 desc, desc->head, desc->tail);
+	desc->head = 0;
+	desc->tail = 0;
+	desc->is_in_error = 0;
+}
+
+static int guc_action_register_ct_buffer(struct intel_guc *guc,
+					 u32 desc_addr,
+					 u32 type)
+{
+	u32 action[] = {
+		INTEL_GUC_ACTION_REGISTER_COMMAND_TRANSPORT_BUFFER,
+		desc_addr,
+		sizeof(struct guc_ct_buffer_desc),
+		type
+	};
+	int err;
+
+	/* Can't use generic send(), CT registration must go over MMIO */
+	err = intel_guc_send_mmio(guc, action, ARRAY_SIZE(action));
+	if (err)
+		DRM_ERROR("CT: register %s buffer failed; err=%d\n",
+			  guc_ct_buffer_type_to_str(type), err);
+	return err;
+}
+
+static int guc_action_deregister_ct_buffer(struct intel_guc *guc,
+					   u32 owner,
+					   u32 type)
+{
+	u32 action[] = {
+		INTEL_GUC_ACTION_DEREGISTER_COMMAND_TRANSPORT_BUFFER,
+		owner,
+		type
+	};
+	int err;
+
+	/* Can't use generic send(), CT deregistration must go over MMIO */
+	err = intel_guc_send_mmio(guc, action, ARRAY_SIZE(action));
+	if (err)
+		DRM_ERROR("CT: deregister %s buffer failed; owner=%d err=%d\n",
+			  guc_ct_buffer_type_to_str(type), owner, err);
+	return err;
+}
+
+static bool ctch_is_open(struct intel_guc_ct_channel *ctch)
+{
+	return ctch->vma != NULL;
+}
+
+static int ctch_init(struct intel_guc *guc,
+		     struct intel_guc_ct_channel *ctch)
+{
+	struct i915_vma *vma;
+	void *blob;
+	int err;
+	int i;
+
+	GEM_BUG_ON(ctch->vma);
+
+	/* We allocate 1 page to hold both descriptors and both buffers.
+	 *       ___________.....................
+	 *      |desc (SEND)|                   :
+	 *      |___________|                   PAGE/4
+	 *      :___________....................:
+	 *      |desc (RECV)|                   :
+	 *      |___________|                   PAGE/4
+	 *      :_______________________________:
+	 *      |cmds (SEND)                    |
+	 *      |                               PAGE/4
+	 *      |_______________________________|
+	 *      |cmds (RECV)                    |
+	 *      |                               PAGE/4
+	 *      |_______________________________|
+	 *
+	 * Each message can use a maximum of 32 dwords and we don't expect to
+	 * have more than 1 in flight at any time, so we have enough space.
+	 * Some logic further ahead will rely on the fact that there is only 1
+	 * page and that it is always mapped, so if the size is changed the
+	 * other code will need updating as well.
+	 */
+
+	/* allocate vma */
+	vma = intel_guc_allocate_vma(guc, PAGE_SIZE);
+	if (IS_ERR(vma)) {
+		err = PTR_ERR(vma);
+		goto err_out;
+	}
+	ctch->vma = vma;
+
+	/* map first page */
+	blob = i915_gem_object_pin_map(vma->obj, I915_MAP_WB);
+	if (IS_ERR(blob)) {
+		err = PTR_ERR(blob);
+		goto err_vma;
+	}
+	DRM_DEBUG_DRIVER("CT: vma base=%#x\n", guc_ggtt_offset(ctch->vma));
+
+	/* store pointers to desc and cmds */
+	for (i = 0; i < ARRAY_SIZE(ctch->ctbs); i++) {
+		GEM_BUG_ON((i != CTB_SEND) && (i != CTB_RECV));
+		ctch->ctbs[i].desc = blob + PAGE_SIZE/4 * i;
+		ctch->ctbs[i].cmds = blob + PAGE_SIZE/4 * i + PAGE_SIZE/2;
+	}
+
+	return 0;
+
+err_vma:
+	i915_vma_unpin_and_release(&ctch->vma);
+err_out:
+	DRM_DEBUG_DRIVER("CT: channel %d initialization failed; err=%d\n",
+			 ctch->owner, err);
+	return err;
+}
+
+static void ctch_fini(struct intel_guc *guc,
+		      struct intel_guc_ct_channel *ctch)
+{
+	GEM_BUG_ON(!ctch->vma);
+
+	i915_gem_object_unpin_map(ctch->vma->obj);
+	i915_vma_unpin_and_release(&ctch->vma);
+}
+
+static int ctch_open(struct intel_guc *guc,
+		     struct intel_guc_ct_channel *ctch)
+{
+	u32 base;
+	int err;
+	int i;
+
+	DRM_DEBUG_DRIVER("CT: channel %d reopen=%s\n",
+			 ctch->owner, yesno(ctch_is_open(ctch)));
+
+	if (!ctch->vma) {
+		err = ctch_init(guc, ctch);
+		if (unlikely(err))
+			goto err_out;
+	}
+
+	/* vma should be already allocated and map'ed */
+	base = guc_ggtt_offset(ctch->vma);
+
+	/* (re)initialize descriptors
+	 * cmds buffers are in the second half of the blob page
+	 */
+	for (i = 0; i < ARRAY_SIZE(ctch->ctbs); i++) {
+		GEM_BUG_ON((i != CTB_SEND) && (i != CTB_RECV));
+		guc_ct_buffer_desc_init(ctch->ctbs[i].desc,
+					base + PAGE_SIZE/4 * i + PAGE_SIZE/2,
+					PAGE_SIZE/4,
+					ctch->owner);
+	}
+
+	/* register buffers, starting wirh RECV buffer
+	 * descriptors are in first half of the blob
+	 */
+	err = guc_action_register_ct_buffer(guc,
+					    base + PAGE_SIZE/4 * CTB_RECV,
+					    INTEL_GUC_CT_BUFFER_TYPE_RECV);
+	if (unlikely(err))
+		goto err_fini;
+
+	err = guc_action_register_ct_buffer(guc,
+					    base + PAGE_SIZE/4 * CTB_SEND,
+					    INTEL_GUC_CT_BUFFER_TYPE_SEND);
+	if (unlikely(err))
+		goto err_deregister;
+
+	return 0;
+
+err_deregister:
+	guc_action_deregister_ct_buffer(guc,
+					ctch->owner,
+					INTEL_GUC_CT_BUFFER_TYPE_RECV);
+err_fini:
+	ctch_fini(guc, ctch);
+err_out:
+	DRM_ERROR("CT: can't open channel %d; err=%d\n", ctch->owner, err);
+	return err;
+}
+
+static void ctch_close(struct intel_guc *guc,
+		       struct intel_guc_ct_channel *ctch)
+{
+	GEM_BUG_ON(!ctch_is_open(ctch));
+
+	guc_action_deregister_ct_buffer(guc,
+					ctch->owner,
+					INTEL_GUC_CT_BUFFER_TYPE_SEND);
+	guc_action_deregister_ct_buffer(guc,
+					ctch->owner,
+					INTEL_GUC_CT_BUFFER_TYPE_RECV);
+	ctch_fini(guc, ctch);
+}
+
+static u32 ctch_get_next_fence(struct intel_guc_ct_channel *ctch)
+{
+	/* For now it's trivial */
+	return ++ctch->next_fence;
+}
+
+static int ctb_write(struct intel_guc_ct_buffer *ctb,
+		     const u32 *action,
+		     u32 len /* in dwords */,
+		     u32 fence)
+{
+	struct guc_ct_buffer_desc *desc = ctb->desc;
+	u32 head = desc->head / 4;	/* in dwords */
+	u32 tail = desc->tail / 4;	/* in dwords */
+	u32 size = desc->size / 4;	/* in dwords */
+	u32 used;			/* in dwords */
+	u32 header;
+	u32 *cmds = ctb->cmds;
+	unsigned int i;
+
+	GEM_BUG_ON(desc->size % 4);
+	GEM_BUG_ON(desc->head % 4);
+	GEM_BUG_ON(desc->tail % 4);
+	GEM_BUG_ON(tail >= size);
+
+	/*
+	 * tail == head condition indicates empty. GuC FW does not support
+	 * using up the entire buffer to get tail == head meaning full.
+	 */
+	if (tail < head)
+		used = (size - head) + tail;
+	else
+		used = tail - head;
+
+	/* make sure there is a space including extra dw for the fence */
+	if (unlikely(used + len + 1 >= size))
+		return -ENOSPC;
+
+	/* Write the message. The format is the following:
+	 * DW0: header (including action code)
+	 * DW1: fence
+	 * DW2+: action data
+	 */
+	header = (len << GUC_CT_MSG_LEN_SHIFT) |
+		 (GUC_CT_MSG_WRITE_FENCE_TO_DESC) |
+		 (action[0] << GUC_CT_MSG_ACTION_SHIFT);
+
+	cmds[tail] = header;
+	tail = (tail + 1) % size;
+
+	cmds[tail] = fence;
+	tail = (tail + 1) % size;
+
+	for (i = 1; i < len; i++) {
+		cmds[tail] = action[i];
+		tail = (tail + 1) % size;
+	}
+
+	/* now update desc tail (back in bytes) */
+	desc->tail = tail * 4;
+	GEM_BUG_ON(desc->tail > desc->size);
+
+	return 0;
+}
+
+/* Wait for the response from the GuC.
+ * @fence:	response fence
+ * @status:	placeholder for status
+ * return:	0 response received (status is valid)
+ *		-ETIMEDOUT no response within hardcoded timeout
+ *		-EPROTO no response, ct buffer was in error
+ */
+static int wait_for_response(struct guc_ct_buffer_desc *desc,
+			     u32 fence,
+			     u32 *status)
+{
+	int err;
+
+	/*
+	 * Fast commands should complete in less than 10us, so sample quickly
+	 * up to that length of time, then switch to a slower sleep-wait loop.
+	 * No GuC command should ever take longer than 10ms.
+	 */
+#define done (READ_ONCE(desc->fence) == fence)
+	err = wait_for_us(done, 10);
+	if (err)
+		err = wait_for(done, 10);
+#undef done
+
+	if (unlikely(err)) {
+		DRM_ERROR("CT: fence %u failed; reported fence=%u\n",
+			  fence, desc->fence);
+
+		if (WARN_ON(desc->is_in_error)) {
+			/* Something went wrong with the messaging, try to reset
+			 * the buffer and hope for the best
+			 */
+			guc_ct_buffer_desc_reset(desc);
+			err = -EPROTO;
+		}
+	}
+
+	*status = desc->status;
+	return err;
+}
+
+static int ctch_send(struct intel_guc *guc,
+		     struct intel_guc_ct_channel *ctch,
+		     const u32 *action,
+		     u32 len,
+		     u32 *status)
+{
+	struct intel_guc_ct_buffer *ctb = &ctch->ctbs[CTB_SEND];
+	struct guc_ct_buffer_desc *desc = ctb->desc;
+	u32 fence;
+	int err;
+
+	GEM_BUG_ON(!ctch_is_open(ctch));
+	GEM_BUG_ON(!len);
+	GEM_BUG_ON(len & ~GUC_CT_MSG_LEN_MASK);
+
+	fence = ctch_get_next_fence(ctch);
+	err = ctb_write(ctb, action, len, fence);
+	if (unlikely(err))
+		return err;
+
+	intel_guc_notify(guc);
+
+	err = wait_for_response(desc, fence, status);
+	if (unlikely(err))
+		return err;
+	if (*status != INTEL_GUC_STATUS_SUCCESS)
+		return -EIO;
+	return 0;
+}
+
+/*
+ * Command Transport (CT) buffer based GuC send function.
+ */
+static int intel_guc_send_ct(struct intel_guc *guc, const u32 *action, u32 len)
+{
+	struct intel_guc_ct_channel *ctch = &guc->ct.host_channel;
+	u32 status = ~0; /* undefined */
+	int err;
+
+	mutex_lock(&guc->send_mutex);
+
+	err = ctch_send(guc, ctch, action, len, &status);
+	if (unlikely(err)) {
+		DRM_ERROR("CT: send action %#X failed; err=%d status=%#X\n",
+			  action[0], err, status);
+	}
+
+	mutex_unlock(&guc->send_mutex);
+	return err;
+}
+
+/**
+ * Enable buffer based command transport
+ * Shall only be called for platforms with HAS_GUC_CT.
+ * @guc:	the guc
+ * return:	0 on success
+ *		non-zero on failure
+ */
+int intel_guc_enable_ct(struct intel_guc *guc)
+{
+	struct drm_i915_private *dev_priv = guc_to_i915(guc);
+	struct intel_guc_ct_channel *ctch = &guc->ct.host_channel;
+	int err;
+
+	GEM_BUG_ON(!HAS_GUC_CT(dev_priv));
+
+	err = ctch_open(guc, ctch);
+	if (unlikely(err))
+		return err;
+
+	/* Switch into cmd transport buffer based send() */
+	guc->send = intel_guc_send_ct;
+	DRM_INFO("CT: %s\n", enableddisabled(true));
+	return 0;
+}
+
+/**
+ * Disable buffer based command transport.
+ * Shall only be called for platforms with HAS_GUC_CT.
+ * @guc: the guc
+ */
+void intel_guc_disable_ct(struct intel_guc *guc)
+{
+	struct drm_i915_private *dev_priv = guc_to_i915(guc);
+	struct intel_guc_ct_channel *ctch = &guc->ct.host_channel;
+
+	GEM_BUG_ON(!HAS_GUC_CT(dev_priv));
+
+	if (!ctch_is_open(ctch))
+		return;
+
+	ctch_close(guc, ctch);
+
+	/* Disable send */
+	guc->send = intel_guc_send_nop;
+	DRM_INFO("CT: %s\n", enableddisabled(false));
+}
diff --git a/drivers/gpu/drm/i915/intel_guc_ct.h b/drivers/gpu/drm/i915/intel_guc_ct.h
new file mode 100644
index 0000000..6d97f36
--- /dev/null
+++ b/drivers/gpu/drm/i915/intel_guc_ct.h
@@ -0,0 +1,86 @@
+/*
+ * Copyright © 2016-2017 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#ifndef _INTEL_GUC_CT_H_
+#define _INTEL_GUC_CT_H_
+
+struct intel_guc;
+struct i915_vma;
+
+#include "intel_guc_fwif.h"
+
+/**
+ * DOC: Command Transport (CT).
+ *
+ * Buffer based command transport is a replacement for MMIO based mechanism.
+ * It can be used to perform both host-2-guc and guc-to-host communication.
+ */
+
+/** Represents single command transport buffer.
+ *
+ * A single command transport buffer consists of two parts, the header
+ * record (command transport buffer descriptor) and the actual buffer which
+ * holds the commands.
+ *
+ * @desc: pointer to the buffer descriptor
+ * @cmds: pointer to the commands buffer
+ */
+struct intel_guc_ct_buffer {
+	struct guc_ct_buffer_desc *desc;
+	u32 *cmds;
+};
+
+/** Represents pair of command transport buffers.
+ *
+ * Buffers go in pairs to allow bi-directional communication.
+ * To simplify the code we place both of them in the same vma.
+ * Buffers from the same pair must share unique owner id.
+ *
+ * @vma: pointer to the vma with pair of CT buffers
+ * @ctbs: buffers for sending(0) and receiving(1) commands
+ * @owner: unique identifier
+ * @next_fence: fence to be used with next send command
+ */
+struct intel_guc_ct_channel {
+	struct i915_vma *vma;
+	struct intel_guc_ct_buffer ctbs[2];
+	u32 owner;
+	u32 next_fence;
+};
+
+/** Holds all command transport channels.
+ *
+ * @host_channel: main channel used by the host
+ */
+struct intel_guc_ct {
+	struct intel_guc_ct_channel host_channel;
+	/* other channels are tbd */
+};
+
+void intel_guc_ct_init_early(struct intel_guc_ct *ct);
+
+/* XXX: move to intel_uc.h ? don't fit there either */
+int intel_guc_enable_ct(struct intel_guc *guc);
+void intel_guc_disable_ct(struct intel_guc *guc);
+
+#endif /* _INTEL_GUC_CT_H_ */
diff --git a/drivers/gpu/drm/i915/intel_guc_fwif.h b/drivers/gpu/drm/i915/intel_guc_fwif.h
index 6156845..5fa2860 100644
--- a/drivers/gpu/drm/i915/intel_guc_fwif.h
+++ b/drivers/gpu/drm/i915/intel_guc_fwif.h
@@ -331,6 +331,47 @@ struct guc_stage_desc {
 	u64 desc_private;
 } __packed;
 
+/*
+ * Describes single command transport buffer.
+ * Used by both guc-master and clients.
+ */
+struct guc_ct_buffer_desc {
+	u32 addr;		/* gfx address */
+	u64 host_private;	/* host private data */
+	u32 size;		/* size in bytes */
+	u32 head;		/* offset updated by GuC*/
+	u32 tail;		/* offset updated by owner */
+	u32 is_in_error;	/* error indicator */
+	u32 fence;		/* fence updated by GuC */
+	u32 status;		/* status updated by GuC */
+	u32 owner;		/* id of the channel owner */
+	u32 owner_sub_id;	/* owner-defined field for extra tracking */
+	u32 reserved[5];
+} __packed;
+
+/* Type of command transport buffer */
+#define INTEL_GUC_CT_BUFFER_TYPE_SEND	0x0u
+#define INTEL_GUC_CT_BUFFER_TYPE_RECV	0x1u
+
+/*
+ * Definition of the command transport message header (DW0)
+ *
+ * bit[4..0]	message len (in dwords)
+ * bit[7..5]	reserved
+ * bit[8]	write fence to desc
+ * bit[9]	write status to H2G buff
+ * bit[10]	send status (via G2H)
+ * bit[15..11]	reserved
+ * bit[31..16]	action code
+ */
+#define GUC_CT_MSG_LEN_SHIFT			0
+#define GUC_CT_MSG_LEN_MASK			0x1F
+#define GUC_CT_MSG_WRITE_FENCE_TO_DESC		(1 << 8)
+#define GUC_CT_MSG_WRITE_STATUS_TO_BUFF		(1 << 9)
+#define GUC_CT_MSG_SEND_STATUS			(1 << 10)
+#define GUC_CT_MSG_ACTION_SHIFT			16
+#define GUC_CT_MSG_ACTION_MASK			0xFFFF
+
 #define GUC_FORCEWAKE_RENDER	(1 << 0)
 #define GUC_FORCEWAKE_MEDIA	(1 << 1)
 
@@ -515,6 +556,8 @@ enum intel_guc_action {
 	INTEL_GUC_ACTION_EXIT_S_STATE = 0x502,
 	INTEL_GUC_ACTION_SLPC_REQUEST = 0x3003,
 	INTEL_GUC_ACTION_AUTHENTICATE_HUC = 0x4000,
+	INTEL_GUC_ACTION_REGISTER_COMMAND_TRANSPORT_BUFFER = 0x4505,
+	INTEL_GUC_ACTION_DEREGISTER_COMMAND_TRANSPORT_BUFFER = 0x4506,
 	INTEL_GUC_ACTION_UK_LOG_ENABLE_LOGGING = 0x0E000,
 	INTEL_GUC_ACTION_LIMIT
 };
diff --git a/drivers/gpu/drm/i915/intel_uc.c b/drivers/gpu/drm/i915/intel_uc.c
index 31dc8c3..d17029c 100644
--- a/drivers/gpu/drm/i915/intel_uc.c
+++ b/drivers/gpu/drm/i915/intel_uc.c
@@ -105,6 +105,8 @@ void intel_uc_init_early(struct drm_i915_private *dev_priv)
 {
 	struct intel_guc *guc = &dev_priv->guc;
 
+	intel_guc_ct_init_early(&guc->ct);
+
 	mutex_init(&guc->send_mutex);
 	guc->send = intel_guc_send_nop;
 	guc->notify = guc_write_irq_trigger;
@@ -288,14 +290,24 @@ static void guc_init_send_regs(struct intel_guc *guc)
 
 static int guc_enable_communication(struct intel_guc *guc)
 {
-	/* XXX: placeholder for alternate setup */
+	struct drm_i915_private *dev_priv = guc_to_i915(guc);
+
 	guc_init_send_regs(guc);
+
+	if (HAS_GUC_CT(dev_priv))
+		return intel_guc_enable_ct(guc);
+
 	guc->send = intel_guc_send_mmio;
 	return 0;
 }
 
 static void guc_disable_communication(struct intel_guc *guc)
 {
+	struct drm_i915_private *dev_priv = guc_to_i915(guc);
+
+	if (HAS_GUC_CT(dev_priv))
+		intel_guc_disable_ct(guc);
+
 	guc->send = intel_guc_send_nop;
 }
 
@@ -442,6 +454,11 @@ int intel_guc_send_mmio(struct intel_guc *guc, const u32 *action, u32 len)
 	GEM_BUG_ON(!len);
 	GEM_BUG_ON(len > guc->send_regs.count);
 
+	/* If CT is available, we expect to use MMIO only during init/fini */
+	GEM_BUG_ON(HAS_GUC_CT(dev_priv) &&
+		*action != INTEL_GUC_ACTION_REGISTER_COMMAND_TRANSPORT_BUFFER &&
+		*action != INTEL_GUC_ACTION_DEREGISTER_COMMAND_TRANSPORT_BUFFER);
+
 	mutex_lock(&guc->send_mutex);
 	intel_uncore_forcewake_get(dev_priv, guc->send_regs.fw_domains);
 
diff --git a/drivers/gpu/drm/i915/intel_uc.h b/drivers/gpu/drm/i915/intel_uc.h
index 930f2e1..fb1d640 100644
--- a/drivers/gpu/drm/i915/intel_uc.h
+++ b/drivers/gpu/drm/i915/intel_uc.h
@@ -27,7 +27,7 @@
 #include "intel_guc_fwif.h"
 #include "i915_guc_reg.h"
 #include "intel_ringbuffer.h"
-
+#include "intel_guc_ct.h"
 #include "i915_vma.h"
 
 struct drm_i915_gem_request;
@@ -173,6 +173,7 @@ struct intel_guc_log {
 struct intel_guc {
 	struct intel_uc_fw fw;
 	struct intel_guc_log log;
+	struct intel_guc_ct ct;
 
 	/* intel_guc_recv interrupt related state */
 	bool interrupts_enabled;
-- 
2.7.4

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