drm/xe: Fix and re-enable xe_print_blob_ascii85()

Commit 70fb86a85d ("drm/xe: Revert some changes that break a mesa
debug tool") partially reverted some changes to workaround breakage
caused to mesa tools. However, in doing so it also broke fetching the
GuC log via debugfs since xe_print_blob_ascii85() simply bails out.

The fix is to avoid the extra newlines: the devcoredump interface is
line-oriented and adding random newlines in the middle breaks it. If a
tool is able to parse it by looking at the data and checking for chars
that are out of the ascii85 space, it can still do so. A format change
that breaks the line-oriented output on devcoredump however needs better
coordination with existing tools.

v2: Add suffix description comment
v3: Reword explanation of xe_print_blob_ascii85() calling drm_puts()
    in a loop

Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Julia Filipchuk <julia.filipchuk@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: stable@vger.kernel.org
Fixes: 70fb86a85d ("drm/xe: Revert some changes that break a mesa debug tool")
Fixes: ec1455ce7e ("drm/xe/devcoredump: Add ASCII85 dump helper function")
Link: https://patchwork.freedesktop.org/patch/msgid/20250123202307.95103-2-jose.souza@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
(cherry picked from commit 2c95bbf5002776117a69caed3b31c10bf7341bec)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_devcoredump.c

@@ -391,42 +391,34 @@ int xe_devcoredump_init(struct xe_device *xe)
 /**
  * xe_print_blob_ascii85 - print a BLOB to some useful location in ASCII85
  *
- * The output is split to multiple lines because some print targets, e.g. dmesg
- * cannot handle arbitrarily long lines. Note also that printing to dmesg in
- * piece-meal fashion is not possible, each separate call to drm_puts() has a
- * line-feed automatically added! Therefore, the entire output line must be
- * constructed in a local buffer first, then printed in one atomic output call.
+ * The output is split into multiple calls to drm_puts() because some print
+ * targets, e.g. dmesg, cannot handle arbitrarily long lines. These targets may
+ * add newlines, as is the case with dmesg: each drm_puts() call creates a
+ * separate line.
  *
  * There is also a scheduler yield call to prevent the 'task has been stuck for
  * 120s' kernel hang check feature from firing when printing to a slow target
  * such as dmesg over a serial port.
  *
- * TODO: Add compression prior to the ASCII85 encoding to shrink huge buffers down.
- *
  * @p: the printer object to output to
  * @prefix: optional prefix to add to output string
+ * @suffix: optional suffix to add at the end. 0 disables it and is
+ *          not added to the output, which is useful when using multiple calls
+ *          to dump data to @p
  * @blob: the Binary Large OBject to dump out
  * @offset: offset in bytes to skip from the front of the BLOB, must be a multiple of sizeof(u32)
  * @size: the size in bytes of the BLOB, must be a multiple of sizeof(u32)
  */
-void xe_print_blob_ascii85(struct drm_printer *p, const char *prefix,
+void xe_print_blob_ascii85(struct drm_printer *p, const char *prefix, char suffix,
 			   const void *blob, size_t offset, size_t size)
 {
 	const u32 *blob32 = (const u32 *)blob;
 	char buff[ASCII85_BUFSZ], *line_buff;
 	size_t line_pos = 0;
 
-	/*
-	 * Splitting blobs across multiple lines is not compatible with the mesa
-	 * debug decoder tool. Note that even dropping the explicit '\n' below
-	 * doesn't help because the GuC log is so big some underlying implementation
-	 * still splits the lines at 512K characters. So just bail completely for
-	 * the moment.
-	 */
-	return;
-
 #define DMESG_MAX_LINE_LEN	800
-#define MIN_SPACE		(ASCII85_BUFSZ + 2)		/* 85 + "\n\0" */
+	/* Always leave space for the suffix char and the \0 */
+#define MIN_SPACE		(ASCII85_BUFSZ + 2)	/* 85 + "<suffix>\0" */
 
 	if (size & 3)
 		drm_printf(p, "Size not word aligned: %zu", size);
@@ -458,7 +450,6 @@ void xe_print_blob_ascii85(struct drm_printer *p, const char *prefix,
 		line_pos += strlen(line_buff + line_pos);
 
 		if ((line_pos + MIN_SPACE) >= DMESG_MAX_LINE_LEN) {
-			line_buff[line_pos++] = '\n';
 			line_buff[line_pos++] = 0;
 
 			drm_puts(p, line_buff);
@@ -470,10 +461,11 @@ void xe_print_blob_ascii85(struct drm_printer *p, const char *prefix,
 		}
 	}
 
-	if (line_pos) {
-		line_buff[line_pos++] = '\n';
-		line_buff[line_pos++] = 0;
+	if (suffix)
+		line_buff[line_pos++] = suffix;
 
+	if (line_pos) {
+		line_buff[line_pos++] = 0;
 		drm_puts(p, line_buff);
 	}
 

drivers/gpu/drm/xe/xe_devcoredump.h

@@ -29,7 +29,7 @@ static inline int xe_devcoredump_init(struct xe_device *xe)
 }
 #endif
 
-void xe_print_blob_ascii85(struct drm_printer *p, const char *prefix,
+void xe_print_blob_ascii85(struct drm_printer *p, const char *prefix, char suffix,
 			   const void *blob, size_t offset, size_t size);
 
 #endif

drivers/gpu/drm/xe/xe_guc_ct.c

@@ -1724,7 +1724,8 @@ void xe_guc_ct_snapshot_print(struct xe_guc_ct_snapshot *snapshot,
 			   snapshot->g2h_outstanding);
 
 		if (snapshot->ctb)
-			xe_print_blob_ascii85(p, "CTB data", snapshot->ctb, 0, snapshot->ctb_size);
+			xe_print_blob_ascii85(p, "CTB data", '\n',
+					      snapshot->ctb, 0, snapshot->ctb_size);
 	} else {
 		drm_puts(p, "CT disabled\n");
 	}

drivers/gpu/drm/xe/xe_guc_log.c

@@ -211,8 +211,10 @@ void xe_guc_log_snapshot_print(struct xe_guc_log_snapshot *snapshot, struct drm_
 	remain = snapshot->size;
 	for (i = 0; i < snapshot->num_chunks; i++) {
 		size_t size = min(GUC_LOG_CHUNK_SIZE, remain);
+		const char *prefix = i ? NULL : "Log data";
+		char suffix = i == snapshot->num_chunks - 1 ? '\n' : 0;
 
-		xe_print_blob_ascii85(p, i ? NULL : "Log data", snapshot->copy[i], 0, size);
+		xe_print_blob_ascii85(p, prefix, suffix, snapshot->copy[i], 0, size);
 		remain -= size;
 	}
 }