[PATCH v3 2/5] drm/xe/guc: Use different error codes for CT errors

[Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>]

Instead of always returning -EPROTO for most errors, use different error
codes based on the error type. -EPROTO is retained for the cases that
are genuine protocol violations by the GuC.  The remaining cases now
report what actually went wrong.

receive_g2h() used to escalate to CT_DEAD + kick_reset() by matching the
two error codes that dequeue_one_g2h() could return on a fatal error.
Invert the check to simplify reset handling.

v2: (Michal)
- Sync order of errors in g2h_read and __guc_ct_send_locked
- For CT errors use EPIPE and for HXG errors use EPROTO
- Convert the non-fatal EPIPE to EPERM in the helper

Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Assisted-by: Claude:claude-opus-5
---
 drivers/gpu/drm/xe/xe_guc_ct.c | 51 +++++++++++++++++++++++++++-------
 1 file changed, 41 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_guc_ct.c b/drivers/gpu/drm/xe/xe_guc_ct.c
index 5c4733da385c..c5a417fef913 100644
--- a/drivers/gpu/drm/xe/xe_guc_ct.c
+++ b/drivers/gpu/drm/xe/xe_guc_ct.c
@@ -947,6 +947,7 @@ static int h2g_write(struct xe_guc_ct *ct, const u32 *action, u32 len,
 	u32 cmd[H2G_CT_HEADERS];
 	u32 tail = h2g->info.tail;
 	u32 full_len;
+	int err;
 	struct iosys_map map = IOSYS_MAP_INIT_OFFSET(&h2g->cmds,
 							 tail * sizeof(u32));
 
@@ -961,12 +962,14 @@ static int h2g_write(struct xe_guc_ct *ct, const u32 *action, u32 len,
 
 		desc_status = desc_read(xe, h2g, status);
 		if (desc_status) {
+			err = -EPIPE;
 			xe_gt_err(gt, "CT write: non-zero status: %u\n", desc_status);
 			goto corrupted;
 		}
 
 		if (tail > h2g->info.size) {
 			desc_write(xe, h2g, status, desc_status | GUC_CTB_STATUS_OVERFLOW);
+			err = -EPIPE;
 			xe_gt_err(gt, "CT write: tail out of range: %u vs %u\n",
 				  tail, h2g->info.size);
 			goto corrupted;
@@ -974,6 +977,7 @@ static int h2g_write(struct xe_guc_ct *ct, const u32 *action, u32 len,
 
 		if (desc_head >= h2g->info.size) {
 			desc_write(xe, h2g, status, desc_status | GUC_CTB_STATUS_OVERFLOW);
+			err = -EPIPE;
 			xe_gt_err(gt, "CT write: invalid head offset %u >= %u)\n",
 				  desc_head, h2g->info.size);
 			goto corrupted;
@@ -1044,7 +1048,7 @@ static int h2g_write(struct xe_guc_ct *ct, const u32 *action, u32 len,
 
 corrupted:
 	CT_DEAD(ct, &ct->ctbs.h2g, H2G_WRITE);
-	return -EPIPE;
+	return err;
 }
 
 static int __guc_ct_send_locked(struct xe_guc_ct *ct, const u32 *action,
@@ -1067,11 +1071,6 @@ static int __guc_ct_send_locked(struct xe_guc_ct *ct, const u32 *action,
 		goto out;
 	}
 
-	if (unlikely(ct->ctbs.h2g.info.broken)) {
-		ret = -EPIPE;
-		goto out;
-	}
-
 	if (ct->state == XE_GUC_CT_STATE_DISABLED) {
 		ret = -ENODEV;
 		goto out;
@@ -1082,6 +1081,11 @@ static int __guc_ct_send_locked(struct xe_guc_ct *ct, const u32 *action,
 		goto out;
 	}
 
+	if (unlikely(ct->ctbs.h2g.info.broken)) {
+		ret = -EPIPE;
+		goto out;
+	}
+
 	xe_gt_assert(gt, xe_guc_ct_enabled(ct));
 
 	if (g2h_fence) {
@@ -1809,10 +1813,12 @@ static int g2h_read(struct xe_guc_ct *ct, u32 *msg, bool fast_path)
 	s32 avail;
 	u32 action;
 	u32 *hxg;
+	int err;
 
 	xe_gt_assert(gt, xe_guc_ct_initialized(ct));
 	lockdep_assert_held(&ct->fast_lock);
 
+	/* Keep in sync with g2h_err_is_fatal() */
 	if (xe_device_wedged(xe))
 		return -ENOTRECOVERABLE;
 
@@ -1823,7 +1829,7 @@ static int g2h_read(struct xe_guc_ct *ct, u32 *msg, bool fast_path)
 		return -ECANCELED;
 
 	if (g2h->info.broken)
-		return -EPIPE;
+		return -EPERM;
 
 	xe_gt_assert(gt, xe_guc_ct_enabled(ct));
 
@@ -1840,6 +1846,7 @@ static int g2h_read(struct xe_guc_ct *ct, u32 *msg, bool fast_path)
 		}
 
 		if (desc_status) {
+			err = -EPIPE;
 			xe_gt_err(gt, "CT read: non-zero status: %u\n", desc_status);
 			goto corrupted;
 		}
@@ -1871,6 +1878,7 @@ static int g2h_read(struct xe_guc_ct *ct, u32 *msg, bool fast_path)
 
 		if (g2h->info.head > g2h->info.size) {
 			desc_write(xe, g2h, status, desc_status | GUC_CTB_STATUS_OVERFLOW);
+			err = -EPIPE;
 			xe_gt_err(gt, "CT read: head out of range: %u vs %u\n",
 				  g2h->info.head, g2h->info.size);
 			goto corrupted;
@@ -1878,6 +1886,7 @@ static int g2h_read(struct xe_guc_ct *ct, u32 *msg, bool fast_path)
 
 		if (desc_tail >= g2h->info.size) {
 			desc_write(xe, g2h, status, desc_status | GUC_CTB_STATUS_OVERFLOW);
+			err = -EPIPE;
 			xe_gt_err(gt, "CT read: invalid tail offset %u >= %u)\n",
 				  desc_tail, g2h->info.size);
 			goto corrupted;
@@ -1898,6 +1907,7 @@ static int g2h_read(struct xe_guc_ct *ct, u32 *msg, bool fast_path)
 			   sizeof(u32));
 	len = FIELD_GET(GUC_CTB_MSG_0_NUM_DWORDS, msg[0]) + GUC_CTB_MSG_MIN_LEN;
 	if (len > avail) {
+		err = -EPIPE;
 		xe_gt_err(gt, "G2H channel broken on read, avail=%d, len=%d, reset required\n",
 			  avail, len);
 		goto corrupted;
@@ -1950,7 +1960,7 @@ static int g2h_read(struct xe_guc_ct *ct, u32 *msg, bool fast_path)
 
 corrupted:
 	CT_DEAD(ct, &ct->ctbs.g2h, G2H_READ);
-	return -EPROTO;
+	return err;
 }
 
 static void g2h_fast_path(struct xe_guc_ct *ct, u32 *msg, u32 len)
@@ -2042,6 +2052,27 @@ static int dequeue_one_g2h(struct xe_guc_ct *ct)
 	return 1;
 }
 
+/*
+ * Errors reported by dequeue_one_g2h() come in two flavours: either the channel
+ * is simply not available right now, which is expected and handled gracefully,
+ * or the channel state or the message itself is inconsistent, in which case the
+ * only way forward is to declare the CT dead and reset the GuC. Since the
+ * former is a short and well known list, check against that and treat anything
+ * else as fatal, so that new error codes don't silently escape the escalation.
+ */
+static bool g2h_err_is_fatal(int err)
+{
+	switch (err) {
+	case -ENOTRECOVERABLE:	/* device wedged */
+	case -ENODEV:		/* CT disabled */
+	case -ECANCELED:	/* CT stopped */
+	case -EPERM:		/* CT already declared broken */
+		return false;
+	default:
+		return true;
+	}
+}
+
 static void receive_g2h(struct xe_guc_ct *ct)
 {
 	bool ongoing;
@@ -2079,8 +2110,8 @@ static void receive_g2h(struct xe_guc_ct *ct)
 		ret = dequeue_one_g2h(ct);
 		mutex_unlock(&ct->lock);
 
-		if (unlikely(ret == -EPROTO || ret == -EOPNOTSUPP)) {
-			xe_gt_err(ct_to_gt(ct), "CT dequeue failed: %d\n", ret);
+		if (unlikely(ret < 0 && g2h_err_is_fatal(ret))) {
+			xe_gt_err(ct_to_gt(ct), "CT dequeue failed (%pe)\n", ERR_PTR(ret));
 			CT_DEAD(ct, NULL, G2H_RECV);
 			kick_reset(ct);
 		}
-- 
2.55.0