drm/xe/devcoredump: Add ASCII85 dump helper function

There is a need to include the GuC log and other large binary objects
in core dumps and via dmesg. So add a helper for dumping to a printer
function via conversion to ASCII85 encoding.

Another issue with dumping such a large buffer is that it can be slow,
especially if dumping to dmesg over a serial port. So add a yield to
prevent the 'task has been stuck for 120s' kernel hang check feature
from firing.

v2: Add a prefix to the output string. Fix memory allocation bug.
v3: Correct a string size calculation and clean up a define (review
feedback from Julia F).

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Julia Filipchuk <julia.filipchuk@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241003004611.2323493-5-John.C.Harrison@Intel.com

drivers/gpu/drm/xe/xe_devcoredump.c

@@ -6,6 +6,7 @@
 #include "xe_devcoredump.h"
 #include "xe_devcoredump_types.h"
 
+#include <linux/ascii85.h>
 #include <linux/devcoredump.h>
 #include <generated/utsrelease.h>
 
@@ -315,3 +316,89 @@ int xe_devcoredump_init(struct xe_device *xe)
 }
 
 #endif
+
+/**
+ * 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.
+ *
+ * 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
+ * @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,
+			   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;
+
+#define DMESG_MAX_LINE_LEN	800
+#define MIN_SPACE		(ASCII85_BUFSZ + 2)		/* 85 + "\n\0" */
+
+	if (size & 3)
+		drm_printf(p, "Size not word aligned: %zu", size);
+	if (offset & 3)
+		drm_printf(p, "Offset not word aligned: %zu", size);
+
+	line_buff = kzalloc(DMESG_MAX_LINE_LEN, GFP_KERNEL);
+	if (IS_ERR_OR_NULL(line_buff)) {
+		drm_printf(p, "Failed to allocate line buffer: %pe", line_buff);
+		return;
+	}
+
+	blob32 += offset / sizeof(*blob32);
+	size /= sizeof(*blob32);
+
+	if (prefix) {
+		strscpy(line_buff, prefix, DMESG_MAX_LINE_LEN - MIN_SPACE - 2);
+		line_pos = strlen(line_buff);
+
+		line_buff[line_pos++] = ':';
+		line_buff[line_pos++] = ' ';
+	}
+
+	while (size--) {
+		u32 val = *(blob32++);
+
+		strscpy(line_buff + line_pos, ascii85_encode(val, buff),
+			DMESG_MAX_LINE_LEN - line_pos);
+		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);
+
+			line_pos = 0;
+
+			/* Prevent 'stuck thread' time out errors */
+			cond_resched();
+		}
+	}
+
+	if (line_pos) {
+		line_buff[line_pos++] = '\n';
+		line_buff[line_pos++] = 0;
+
+		drm_puts(p, line_buff);
+	}
+
+	kfree(line_buff);
+
+#undef MIN_SPACE
+#undef DMESG_MAX_LINE_LEN
+}

drivers/gpu/drm/xe/xe_devcoredump.h

@@ -6,6 +6,9 @@
 #ifndef _XE_DEVCOREDUMP_H_
 #define _XE_DEVCOREDUMP_H_
 
+#include <linux/types.h>
+
+struct drm_printer;
 struct xe_device;
 struct xe_sched_job;
 
@@ -23,4 +26,7 @@ static inline int xe_devcoredump_init(struct xe_device *xe)
 }
 #endif
 
+void xe_print_blob_ascii85(struct drm_printer *p, const char *prefix,
+			   const void *blob, size_t offset, size_t size);
+
 #endif