[PATCH 09/15] drm/i915/guc: Prepare to handle messages from CT RECV buffer

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

GuC can respond to our commands not only by updating SEND buffer
descriptor, but can send us message over RECV buffer. Additionally
Guc can also send us unsolicited requests over RECV buffer.
Lets start reading those messages and make placeholders for actual
response/request handlers.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
---
 drivers/gpu/drm/i915/intel_guc_ct.c | 120 ++++++++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_guc_ct.c b/drivers/gpu/drm/i915/intel_guc_ct.c
index c17cb42..dd30c83 100644
--- a/drivers/gpu/drm/i915/intel_guc_ct.c
+++ b/drivers/gpu/drm/i915/intel_guc_ct.c
@@ -414,6 +414,124 @@ static int intel_guc_send_ct(struct intel_guc *guc, const u32 *action, u32 len,
 	return ret;
 }
 
+static inline unsigned int ct_header_get_len(u32 header)
+{
+	return (header >> GUC_CT_MSG_LEN_SHIFT) & GUC_CT_MSG_LEN_MASK;
+}
+
+static inline unsigned int ct_header_get_action(u32 header)
+{
+	return (header >> GUC_CT_MSG_ACTION_SHIFT) & GUC_CT_MSG_ACTION_MASK;
+}
+
+static inline bool ct_header_is_response(u32 header)
+{
+	return !!(header & GUC_CT_MSG_IS_RESPONSE);
+}
+
+static int ctb_read(struct intel_guc_ct_buffer *ctb, u32 *data)
+{
+	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 *cmds = ctb->cmds;
+	s32 available;			/* in dwords */
+	unsigned int len;
+	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);
+	GEM_BUG_ON(head >= size);
+
+	/* tail == head condition indicates empty */
+	available = tail - head;
+	if (available == 0)
+		return -ENODATA;
+
+	/* beware of buffer wrap case */
+	if (available < 0)
+		available += size;
+	GEM_BUG_ON(available < 0);
+
+	data[0] = cmds[head];
+	head = (head + 1) % size;
+
+	/* message len with header */
+	len = ct_header_get_len(data[0]) + 1;
+	if (unlikely(len > (u32)available)) {
+		DRM_ERROR("CT: incomplete message %*phn %*phn %*phn\n",
+			  4, data,
+			  4 * (head + available - 1 > size ?
+			       size - head : available - 1), &cmds[head],
+			  4 * (head + available - 1 > size ?
+			       available - 1 - size + head : 0), &cmds[0]);
+		return -EPROTO;
+	}
+
+	for (i = 1; i < len; i++) {
+		data[i] = cmds[head];
+		head = (head + 1) % size;
+	}
+
+	desc->head = head * 4;
+	return 0;
+}
+
+static int guc_handle_response(struct intel_guc *guc, const u32 *data)
+{
+	u32 header = data[0];
+	u32 len = ct_header_get_len(header) + 1; /* total len with header */
+
+	GEM_BUG_ON(!ct_header_is_response(header));
+	/* beyond header, data shall at least include fence and status */
+	if (unlikely(len < 3)) {
+		DRM_ERROR("CT: corrupted response %*phn\n", 4*len, data);
+		return -EPROTO;
+	}
+
+	return 0;
+}
+
+static int guc_handle_request(struct intel_guc *guc, const u32 *data)
+{
+	u32 header = data[0];
+
+	GEM_BUG_ON(ct_header_is_response(header));
+	/* data layout beyond header is request specific */
+
+	return 0;
+}
+
+static void intel_guc_receive_ct(struct intel_guc *guc)
+{
+	struct intel_guc_ct_channel *ctch = &guc->ct.host_channel;
+	struct intel_guc_ct_buffer *ctb = &ctch->ctbs[CTB_RECV];
+	u32 msg[GUC_CT_MSG_LEN_MASK+1];
+	int err = 0;
+
+	if (!ctch_is_open(ctch))
+		return;
+
+	do {
+		err = ctb_read(ctb, msg);
+		if (err)
+			break;
+
+		if (ct_header_is_response(msg[0]))
+			err = guc_handle_response(guc, msg);
+		else
+			err = guc_handle_request(guc, msg);
+	} while (!err);
+
+	if (GEM_WARN_ON(err == -EPROTO)) {
+		DRM_ERROR("CT: corrupted message detected!\n");
+		ctb->desc->is_in_error = 1;
+	}
+}
+
 /**
  * Enable buffer based command transport
  * Shall only be called for platforms with HAS_GUC_CT.
@@ -435,6 +553,7 @@ int intel_guc_enable_ct(struct intel_guc *guc)
 
 	/* Switch into cmd transport buffer based send() */
 	guc->send = intel_guc_send_ct;
+	guc->recv = intel_guc_receive_ct;
 	DRM_INFO("CT: %s\n", enableddisabled(true));
 	return 0;
 }
@@ -458,5 +577,6 @@ void intel_guc_disable_ct(struct intel_guc *guc)
 
 	/* Disable send */
 	guc->send = intel_guc_send_nop;
+	guc->recv = intel_guc_receive_nop;
 	DRM_INFO("CT: %s\n", enableddisabled(false));
 }
-- 
2.7.4

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