From: Hector Martin <marcan@xxxxxxxxx>
%p4cc is designed for DRM/V4L2 FOURCCs with their specific quirks, but
it's useful to be able to print generic 4-character codes formatted as
an integer. Extend it to add format specifiers for printing generic
32-bit FOURCCs with various endian semantics:
%p4ch Host-endian
%p4cl Little-endian
%p4cb Big-endian
%p4cr Reverse-endian
The endianness determines how bytes are interpreted as a u32, and the
FOURCC is then always printed MSByte-first (this is the opposite of
V4L/DRM FOURCCs). This covers most practical cases, e.g. %p4cr would
allow printing LSByte-first FOURCCs stored in host endian order
(other than the hex form being in character order, not the integer
value).
Signed-off-by: Hector Martin <marcan@xxxxxxxxx>
Signed-off-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx>
---
Documentation/core-api/printk-formats.rst | 32 +++++++++++++++++++++
lib/vsprintf.c | 35 +++++++++++++++++++----
2 files changed, 61 insertions(+), 6 deletions(-)
diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index 5e89497ba314..22c33398ec02 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -625,6 +625,38 @@ Passed by reference.
%p4cc Y10 little-endian (0x20303159)
%p4cc NV12 big-endian (0xb231564e)
+Generic FourCC code
+-------------------
+
+::
+ %p4c[hnbl] gP00 (0x67503030)
+
+Print a generic FourCC code, as both ASCII characters and its numerical
+value as hexadecimal.
+
+The additional ``h``, ``r``, ``b``, and ``l`` specifiers are used to specify
+host, reversed, big or little endian order data respectively. Host endian
+order means the data is interpreted as a 32-bit integer and the most
+significant byte is printed first; that is, the character code as printed
+matches the byte order stored in memory on big-endian systems, and is reversed
+on little-endian systems.
+
+Passed by reference.
+
+Examples for a little-endian machine, given &(u32)0x67503030::
+
+ %p4ch gP00 (0x67503030)
+ %p4cl gP00 (0x67503030)
+ %p4cb 00Pg (0x30305067)
+ %p4cr 00Pg (0x30305067)
+
+Examples for a big-endian machine, given &(u32)0x67503030::
+
+ %p4ch gP00 (0x67503030)
+ %p4cl 00Pg (0x30305067)
+ %p4cb gP00 (0x67503030)
+ %p4cr 00Pg (0x30305067)
+
Thanks
======
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 3c1853a9d1c0..31707499f90f 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1757,27 +1757,50 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc,
char output[sizeof("0123 little-endian (0x01234567)")];
char *p = output;
unsigned int i;
+ bool pix_fmt = false;
u32 orig, val;
- if (fmt[1] != 'c' || fmt[2] != 'c')
+ if (fmt[1] != 'c')
return error_string(buf, end, "(%p4?)", spec);
if (check_pointer(&buf, end, fourcc, spec))
return buf;
orig = get_unaligned(fourcc);
- val = orig & ~BIT(31);
+ switch (fmt[2]) {
+ case 'h':
+ val = orig;
+ break;
+ case 'r':
+ val = orig = swab32(orig);
+ break;
+ case 'l':
+ val = orig = le32_to_cpu(orig);
+ break;
+ case 'b':
+ val = orig = be32_to_cpu(orig);
+ break;
+ case 'c':
+ /* Pixel formats are printed LSB-first */
+ val = swab32(orig & ~BIT(31));
+ pix_fmt = true;
+ break;
+ default:
+ return error_string(buf, end, "(%p4?)", spec);
+ }
for (i = 0; i < sizeof(u32); i++) {
- unsigned char c = val >> (i * 8);
+ unsigned char c = val >> ((3 - i) * 8);
/* Print non-control ASCII characters as-is, dot otherwise */
*p++ = isascii(c) && isprint(c) ? c : '.';
}
- *p++ = ' ';
- strcpy(p, orig & BIT(31) ? "big-endian" : "little-endian");
- p += strlen(p);
+ if (pix_fmt) {
+ *p++ = ' ';
+ strcpy(p, orig & BIT(31) ? "big-endian" : "little-endian");
+ p += strlen(p);
+ }
*p++ = ' ';
*p++ = '(';
--
2.30.2
