drm/xe/gsc: Improve SW proxy error checking and logging

If an error occurs in the GSC<->CSME handshake, the GSC will send a
PROXY_END msg to the driver with the status set to an error code. We
currently don't check the status when receiving a PROXY_END message and
instead check the proxy initialization status in the FWSTS reg;
therefore, while still catching any initialization failures, we lose the
actual returned error code. This can be easily improved by checking the
status value and printing it to dmesg if it's an error.

Signed-off-by: Daniele Ceraolo Spurio <[e-mail]>
Cc: Alan Previn <[e-mail]>
Reviewed-by: Alan Previn <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/xe/xe_gsc_proxy.c

···
 	return 0;
 }
 
-static int validate_proxy_header(struct xe_gsc_proxy_header *header,
+static int validate_proxy_header(struct xe_gt *gt,
+				 struct xe_gsc_proxy_header *header,
 				 u32 source, u32 dest, u32 max_size)
 {
 	u32 type = FIELD_GET(GSC_PROXY_TYPE, header->hdr);
 	u32 length = FIELD_GET(GSC_PROXY_PAYLOAD_LENGTH, header->hdr);
+	int ret = 0;
 
-	if (header->destination != dest || header->source != source)
-		return -ENOEXEC;
+	if (header->destination != dest || header->source != source) {
+		ret = -ENOEXEC;
+		goto out;
+	}
 
-	if (length + PROXY_HDR_SIZE > max_size)
-		return -E2BIG;
+	if (length + PROXY_HDR_SIZE > max_size) {
+		ret = -E2BIG;
+		goto out;
+	}
+
+	/* We only care about the status if this is a message for the driver */
+	if (dest == GSC_PROXY_ADDRESSING_KMD && header->status != 0) {
+		ret = -EIO;
+		goto out;
+	}
 
 	switch (type) {
 	case GSC_PROXY_MSG_TYPE_PROXY_PAYLOAD:
···
 			break;
 		fallthrough;
 	case GSC_PROXY_MSG_TYPE_PROXY_INVALID:
-		return -EIO;
+		ret = -EIO;
+		break;
 	default:
 		break;
 	}
 
-	return 0;
+out:
+	if (ret)
+		xe_gt_err(gt,
+			  "GSC proxy error: s=0x%x[0x%x], d=0x%x[0x%x], t=%u, l=0x%x, st=0x%x\n",
+			  header->source, source, header->destination, dest,
+			  type, length, header->status);
+
+	return ret;
 }
 
 #define proxy_header_wr(xe_, map_, offset_, field_, val_) \
···
 		xe_map_memcpy_from(xe, to_csme_hdr, &gsc->proxy.from_gsc,
 				   reply_offset, PROXY_HDR_SIZE);
 
-		/* stop if this was the last message */
-		if (FIELD_GET(GSC_PROXY_TYPE, to_csme_hdr->hdr) == GSC_PROXY_MSG_TYPE_PROXY_END)
+		/* Check the status and stop if this was the last message */
+		if (FIELD_GET(GSC_PROXY_TYPE, to_csme_hdr->hdr) == GSC_PROXY_MSG_TYPE_PROXY_END) {
+			ret = validate_proxy_header(gt, to_csme_hdr,
+						    GSC_PROXY_ADDRESSING_GSC,
+						    GSC_PROXY_ADDRESSING_KMD,
+						    GSC_PROXY_BUFFER_SIZE - reply_offset);
 			break;
+		}
 
 		/* make sure the GSC-to-CSME proxy header is sane */
-		ret = validate_proxy_header(to_csme_hdr,
+		ret = validate_proxy_header(gt, to_csme_hdr,
 					    GSC_PROXY_ADDRESSING_GSC,
 					    GSC_PROXY_ADDRESSING_CSME,
 					    GSC_PROXY_BUFFER_SIZE - reply_offset);
···
 		}
 
 		/* make sure the CSME-to-GSC proxy header is sane */
-		ret = validate_proxy_header(gsc->proxy.from_csme,
+		ret = validate_proxy_header(gt, gsc->proxy.from_csme,
 					    GSC_PROXY_ADDRESSING_CSME,
 					    GSC_PROXY_ADDRESSING_GSC,
 					    GSC_PROXY_BUFFER_SIZE - reply_offset);