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Subject[PATCH 1/1] lib/vsprintf: Add support for printing V4L2 and DRM fourccs
Date
Add a printk modifier %p4cc (for pixel format) for printing V4L2 and DRM
pixel formats denoted by fourccs. The fourcc encoding is the same for both
so the same implementation can be used.

Suggested-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
Documentation/core-api/printk-formats.rst | 12 ++++
lib/test_printf.c | 17 +++++
lib/vsprintf.c | 86 +++++++++++++++++++++++
3 files changed, 115 insertions(+)

diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index 8ebe46b1af39..7aa0451e06fb 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -545,6 +545,18 @@ For printing netdev_features_t.

Passed by reference.

+V4L2 and DRM FourCC code (pixel format)
+---------------------------------------
+
+::
+
+ %p4cc
+
+Print a FourCC code used by V4L2 or DRM, including format endianness and
+its numerical value as hexadecimal.
+
+Passed by reference.
+
Thanks
======

diff --git a/lib/test_printf.c b/lib/test_printf.c
index 2d9f520d2f27..a14754086707 100644
--- a/lib/test_printf.c
+++ b/lib/test_printf.c
@@ -624,6 +624,22 @@ static void __init fwnode_pointer(void)
software_node_unregister_nodes(softnodes);
}

+static void __init fourcc_pointer(void)
+{
+ struct {
+ u32 code;
+ char *str;
+ } const try[] = {
+ { 0x20104646, "FF(10) little-endian (0x20104646)", },
+ { 0xa0104646, "FF(10) big-endian (0xa0104646)", },
+ { 0x10111213, "(13)(12)(11)(10) little-endian (0x10111213)", },
+ };
+ unsigned int i;
+
+ for (i = 0; i < ARRAY_SIZE(try); i++)
+ test(try[i].str, "%p4cc", &try[i].code);
+}
+
static void __init
errptr(void)
{
@@ -668,6 +684,7 @@ test_pointer(void)
flags();
errptr();
fwnode_pointer();
+ fourcc_pointer();
}

static void __init selftest(void)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 7c488a1ce318..02e7906619c0 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1721,6 +1721,89 @@ char *netdev_bits(char *buf, char *end, const void *addr,
return special_hex_number(buf, end, num, size);
}

+static noinline_for_stack
+char *fourcc_string(char *buf, char *end, const u32 *__fourcc,
+ struct printf_spec spec, const char *fmt)
+{
+#define FOURCC_HEX_CHAR_STR "(xx)"
+#define FOURCC_BIG_ENDIAN_STR " big-endian"
+#define FOURCC_LITTLE_ENDIAN_STR " little-endian"
+#define FOURCC_HEX_NUMBER " (0x01234567)"
+#define FOURCC_STRING_MAX \
+ FOURCC_HEX_CHAR_STR FOURCC_HEX_CHAR_STR FOURCC_HEX_CHAR_STR \
+ FOURCC_HEX_CHAR_STR FOURCC_LITTLE_ENDIAN_STR FOURCC_HEX_NUMBER
+ struct printf_spec my_spec = {
+ .type = FORMAT_TYPE_UINT,
+ .field_width = 2,
+ .flags = SMALL,
+ .base = 16,
+ .precision = -1,
+ };
+ char __s[sizeof(FOURCC_STRING_MAX)];
+ char *s = __s;
+ unsigned int i;
+ /*
+ * The 31st bit defines the endianness of the data, so save its printing
+ * for later.
+ */
+ u32 fourcc = *__fourcc & ~BIT(31);
+ int ret;
+
+ if (check_pointer(&buf, end, __fourcc, spec))
+ return buf;
+
+ if (fmt[1] != 'c' || fmt[2] != 'c')
+ return error_string(buf, end, "(%p4?)", spec);
+
+ for (i = 0; i < sizeof(fourcc); i++, fourcc >>= 8) {
+ unsigned char c = fourcc;
+
+ /* Weed out spaces */
+ if (c == ' ')
+ continue;
+
+ /* Print non-control characters as-is */
+ if (c > ' ') {
+ *s = c;
+ s++;
+ continue;
+ }
+
+ if (WARN_ON_ONCE(sizeof(__s) <
+ (s - __s) + sizeof(FOURCC_HEX_CHAR_STR)))
+ break;
+
+ *s = '(';
+ s++;
+ s = number(s, s + 2, c, my_spec);
+ *s = ')';
+ s++;
+ }
+
+ ret = strscpy(s, *__fourcc & BIT(31) ? FOURCC_BIG_ENDIAN_STR
+ : FOURCC_LITTLE_ENDIAN_STR,
+ sizeof(__s) - (s - __s));
+ if (!WARN_ON_ONCE(ret < 0))
+ s += ret;
+
+ if (!WARN_ON_ONCE(sizeof(__s) <
+ (s - __s) + sizeof(FOURCC_HEX_NUMBER))) {
+ *s = ' ';
+ s++;
+ *s = '(';
+ s++;
+ /* subtract parentheses and the space from the size */
+ special_hex_number(s, s + sizeof(FOURCC_HEX_NUMBER) - 3,
+ *__fourcc, sizeof(u32));
+ s += sizeof(u32) * 2 + 2 /* 0x */;
+ *s = ')';
+ s++;
+ *s = '\0';
+ }
+
+ return string(buf, end, __s, spec);
+}
+
static noinline_for_stack
char *address_val(char *buf, char *end, const void *addr,
struct printf_spec spec, const char *fmt)
@@ -2131,6 +2214,7 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
* correctness of the format string and va_list arguments.
* - 'K' For a kernel pointer that should be hidden from unprivileged users
* - 'NF' For a netdev_features_t
+ * - '4cc' V4L2 or DRM FourCC code, with endianness and raw numerical value.
* - 'h[CDN]' For a variable-length buffer, it prints it as a hex string with
* a certain separator (' ' by default):
* C colon
@@ -2223,6 +2307,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
return restricted_pointer(buf, end, ptr, spec);
case 'N':
return netdev_bits(buf, end, ptr, spec, fmt);
+ case '4':
+ return fourcc_string(buf, end, ptr, spec, fmt);
case 'a':
return address_val(buf, end, ptr, spec, fmt);
case 'd':
--
2.20.1
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