platform/chrome: chromeos_acpi: print hex string for ACPI_TYPE_BUFFER

`element->buffer.pointer` should be binary blob. `%s` doesn't work
perfect for them.

Print hex string for ACPI_TYPE_BUFFER. Also update the documentation
to reflect this.

Fixes: 0a4cad9c11ad ("platform/chrome: Add ChromeOS ACPI device driver")
Cc: [e-mail]
Reviewed-by: Guenter Roeck <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Tzung-Bi Shih <[e-mail]>

Documentation/ABI/testing/sysfs-driver-chromeos-acpi

···
 Description:
 		Returns the verified boot data block shared between the
 		firmware verification step and the kernel verification step
-		(binary).
+		(hex dump).

drivers/platform/chrome/chromeos_acpi.c

···
 	case ACPI_TYPE_STRING:
 		return sysfs_emit(buf, "%s\n", element->string.pointer);
 	case ACPI_TYPE_BUFFER:
-		return sysfs_emit(buf, "%s\n", element->buffer.pointer);
+		{
+			int i, r, at, room_left;
+			const int byte_per_line = 16;
+
+			at = 0;
+			room_left = PAGE_SIZE - 1;
+			for (i = 0; i < element->buffer.length && room_left; i += byte_per_line) {
+				r = hex_dump_to_buffer(element->buffer.pointer + i,
+						       element->buffer.length - i,
+						       byte_per_line, 1, buf + at, room_left,
+						       false);
+				if (r > room_left)
+					goto truncating;
+				at += r;
+				room_left -= r;
+
+				r = sysfs_emit_at(buf, at, "\n");
+				if (!r)
+					goto truncating;
+				at += r;
+				room_left -= r;
+			}
+
+			buf[at] = 0;
+			return at;
+truncating:
+			dev_info_once(dev, "truncating sysfs content for %s\n", name);
+			sysfs_emit_at(buf, PAGE_SIZE - 4, "..\n");
+			return PAGE_SIZE - 1;
+		}
 	default:
 		dev_err(dev, "element type %d not supported\n", element->type);
 		return -EINVAL;