[PATCH 4/7] lib/vsprintf: Add support for generic FOURCCs by extending %p4cc
From: Russell King (Oracle) <hidden>
Date: 2022-09-06 13:19:53
Also in:
asahi, linux-devicetree, linux-doc, linux-gpio
Subsystem:
documentation, library code, the rest, vsprintf · Maintainers:
Jonathan Corbet, Andrew Morton, Linus Torvalds, Petr Mladek, Steven Rostedt
From: Hector Martin <redacted> %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 <redacted> Signed-off-by: Russell King (Oracle) <redacted> --- 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
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel