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@xxxxxxxxxx>
Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
---
Hi folks,
I believe I've addressed comments from Rasmus, Joe and Andy --- variables
that don't need to be negative have remained unsigned though. Thanks for
the suggestions, I believe this is much cleaner than v3.
since v3:
- Remove use of WARN_ON, assume the code is correct instead. A side effect
of this is the code is much easier to understand.
- Check the modifier first before validating the buf pointer.
- Use isascii() and isprint() functions to weed out non-printable
characters.
- Use hex_byte_pack() for printing 8-bit hexadecimal numbers.
- Remove macros, and instead use plain strings.
- Use strcpy() to copy the endianness string, and then strlen() to add its
length.
- Strip the MSB (endianness bit), then use the value as such.
- Assign characters to the buffer and increment active pointer at the same
time.
- Drop __ from variable names.
- Add example to documentation.
Documentation/core-api/printk-formats.rst | 16 +++++++
lib/test_printf.c | 17 ++++++++
lib/vsprintf.c | 52 +++++++++++++++++++++++
3 files changed, 85 insertions(+)
diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index 6d26c5c6ac48..080262d2e030 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -565,6 +565,22 @@ 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.
+
+Examples::
+
+ %p4cc BG12 little-endian (0x32314742)
+
Thanks
======
diff --git a/lib/test_printf.c b/lib/test_printf.c
index 7ac87f18a10f..7fb042542660 100644
--- a/lib/test_printf.c
+++ b/lib/test_printf.c
@@ -649,6 +649,22 @@ static void __init fwnode_pointer(void)
software_node_unregister(&softnodes[0]);
}
+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)
{
@@ -694,6 +710,7 @@ 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 14c9a6af1b23..2be86b302c88 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1733,6 +1733,55 @@ 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)
+{
+ char output[sizeof("(xx)(xx)(xx)(xx) little-endian (0x01234567)")];
+ char *p = output;
+ unsigned int i;
+ u32 val;
+
+ if (fmt[1] != 'c' || fmt[2] != 'c')
+ return error_string(output, end, "(%p4?)", spec);
+
+ if (check_pointer(&buf, end, fourcc, spec))
+ return buf;
+
+ val = *fourcc & ~BIT(31);
+
+ for (i = 0; i < sizeof(*fourcc); i++) {
+ unsigned char c = val >> (i * 8);
+
+ /* Weed out spaces */
+ if (c == ' ')
+ continue;
+
+ /* Print non-control ASCII characters as-is */
+ if (isascii(c) && isprint(c)) {
+ *p++ = c;
+ continue;
+ }
+
+ *p++ = '(';
+ p = hex_byte_pack(p, c);
+ *p++ = ')';
+ }
+
+ strcpy(p, *fourcc & BIT(31) ? " big-endian" : " little-endian");
+ p += strlen(p);
+
+ *p++ = ' ';
+ *p++ = '(';
+ /* subtract parenthesis and the space from the size */
+ p = special_hex_number(p, output + sizeof(output) - 2, *fourcc,
+ sizeof(u32));
+ *p++ = ')';
+ *p = '\0';
+
+ return string(buf, end, output, spec);
+}
+
static noinline_for_stack
char *address_val(char *buf, char *end, const void *addr,
struct printf_spec spec, const char *fmt)
@@ -2162,6 +2211,7 @@ 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
@@ -2259,6 +2309,8 @@ 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':
--
2.27.0
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