[PATCH v2 2/3] lib/vsprintf: Add support for generic FOURCCs by extending %p4cc
From: Aditya Garg
Date: Thu Feb 20 2025 - 11:40:56 EST
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: Aditya Garg <gargaditya08@xxxxxxxx>
---
v2 -> Add this patch
Documentation/core-api/printk-formats.rst | 32 +++++++++++++++++++
lib/test_printf.c | 39 +++++++++++++++++++----
lib/vsprintf.c | 38 ++++++++++++++++++----
scripts/checkpatch.pl | 2 +-
4 files changed, 97 insertions(+), 14 deletions(-)
diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index ecccc0473..9982861fa 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -648,6 +648,38 @@ Examples::
%p4cc Y10 little-endian (0x20303159)
%p4cc NV12 big-endian (0xb231564e)
+Generic FourCC code
+-------------------
+
+::
+ %p4c[hrbl] 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)
+ %p4cr 00Pg (0x30305067)
+ %p4cb 00Pg (0x30305067)
+ %p4cl gP00 (0x67503030)
+
+Examples for a big-endian machine, given &(u32)0x67503030::
+
+ %p4ch gP00 (0x67503030)
+ %p4cr 00Pg (0x30305067)
+ %p4cb gP00 (0x67503030)
+ %p4cl 00Pg (0x30305067)
+
Rust
----
diff --git a/lib/test_printf.c b/lib/test_printf.c
index 59dbe4f9a..ee860327e 100644
--- a/lib/test_printf.c
+++ b/lib/test_printf.c
@@ -776,21 +776,46 @@ static void __init fwnode_pointer(void)
software_node_unregister_node_group(group);
}
+struct fourcc_struct {
+ u32 code;
+ const char *str;
+};
+
+static void __init fourcc_pointer_test(const struct fourcc_struct *fc, size_t n,
+ const char *fmt)
+{
+ size_t i;
+
+ for (i = 0; i < n; i++)
+ test(fc[i].str, fmt, &fc[i].code);
+}
+
static void __init fourcc_pointer(void)
{
- struct {
- u32 code;
- char *str;
- } const try[] = {
+ struct fourcc_struct const try_cc[] = {
{ 0x3231564e, "NV12 little-endian (0x3231564e)", },
{ 0xb231564e, "NV12 big-endian (0xb231564e)", },
{ 0x10111213, ".... little-endian (0x10111213)", },
{ 0x20303159, "Y10 little-endian (0x20303159)", },
};
- unsigned int i;
+ struct fourcc_struct const try_ch = {
+ 0x41424344, "ABCD (0x41424344)",
+ };
+ struct fourcc_struct const try_cr = {
+ 0x41424344, "DCBA (0x44434241)",
+ };
+ struct fourcc_struct const try_cl = {
+ le32_to_cpu(0x41424344), "ABCD (0x41424344)",
+ };
+ struct fourcc_struct const try_cb = {
+ be32_to_cpu(0x41424344), "ABCD (0x41424344)",
+ };
- for (i = 0; i < ARRAY_SIZE(try); i++)
- test(try[i].str, "%p4cc", &try[i].code);
+ fourcc_pointer_test(try_cc, ARRAY_SIZE(try_cc), "%p4cc");
+ fourcc_pointer_test(&try_ch, 1, "%p4ch");
+ fourcc_pointer_test(&try_cr, 1, "%p4cr");
+ fourcc_pointer_test(&try_cl, 1, "%p4cl");
+ fourcc_pointer_test(&try_cb, 1, "%p4cb");
}
static void __init
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 56fe96319..13733a4da 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1781,27 +1781,53 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc,
char output[sizeof("0123 little-endian (0x01234567)")];
char *p = output;
unsigned int i;
+ bool pixel_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':
+ orig = swab32(orig);
+ val = orig;
+ break;
+ case 'l':
+ orig = le32_to_cpu(orig);
+ val = orig;
+ break;
+ case 'b':
+ orig = be32_to_cpu(orig);
+ val = orig;
+ break;
+ case 'c':
+ /* Pixel formats are printed LSB-first */
+ val = swab32(orig & ~BIT(31));
+ pixel_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 (pixel_fmt) {
+ *p++ = ' ';
+ strcpy(p, orig & BIT(31) ? "big-endian" : "little-endian");
+ p += strlen(p);
+ }
*p++ = ' ';
*p++ = '(';
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 7b28ad331..21516f753 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6904,7 +6904,7 @@ sub process {
($extension eq "f" &&
defined $qualifier && $qualifier !~ /^w/) ||
($extension eq "4" &&
- defined $qualifier && $qualifier !~ /^cc/)) {
+ defined $qualifier && $qualifier !~ /^c[chlbr]/)) {
$bad_specifier = $specifier;
last;
}
--
2.43.0