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137 lines
3.9 KiB
Diff
137 lines
3.9 KiB
Diff
From 5c8936e9fd03a27cce9ce1f2fe0a4e8ad7ea2369 Mon Sep 17 00:00:00 2001
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From: Hector Martin <marcan@marcan.st>
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Date: Tue, 1 Feb 2022 00:40:51 +0900
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Subject: [PATCH 135/171] lib/vsprintf: Add support for generic FOURCCs by
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extending %p4cc
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%p4cc is designed for DRM/V4L2 FOURCCs with their specific quirks, but
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it's useful to be able to print generic 4-character codes formatted as
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an integer. Extend it to add format specifiers for printing generic
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32-bit FOURCCs with various endian semantics:
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%p4ch Host-endian
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%p4cl Little-endian
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%p4cb Big-endian
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%p4cr Reverse-endian
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The endianness determines how bytes are interpreted as a u32, and the
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FOURCC is then always printed MSByte-first (this is the opposite of
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V4L/DRM FOURCCs). This covers most practical cases, e.g. %p4cr would
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allow printing LSByte-first FOURCCs stored in host endian order
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(other than the hex form being in character order, not the integer
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value).
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Signed-off-by: Hector Martin <marcan@marcan.st>
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---
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Documentation/core-api/printk-formats.rst | 32 +++++++++++++++++++++
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lib/vsprintf.c | 35 +++++++++++++++++++----
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2 files changed, 61 insertions(+), 6 deletions(-)
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diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
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index 5e89497ba314..22c33398ec02 100644
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--- a/Documentation/core-api/printk-formats.rst
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+++ b/Documentation/core-api/printk-formats.rst
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@@ -625,6 +625,38 @@ Examples::
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%p4cc Y10 little-endian (0x20303159)
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%p4cc NV12 big-endian (0xb231564e)
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+Generic FourCC code
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+-------------------
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+
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+::
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+ %p4c[hnbl] gP00 (0x67503030)
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+
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+Print a generic FourCC code, as both ASCII characters and its numerical
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+value as hexadecimal.
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+
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+The additional ``h``, ``r``, ``b``, and ``l`` specifiers are used to specify
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+host, reversed, big or little endian order data respectively. Host endian
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+order means the data is interpreted as a 32-bit integer and the most
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+significant byte is printed first; that is, the character code as printed
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+matches the byte order stored in memory on big-endian systems, and is reversed
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+on little-endian systems.
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+
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+Passed by reference.
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+
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+Examples for a little-endian machine, given &(u32)0x67503030::
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+
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+ %p4ch gP00 (0x67503030)
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+ %p4cl gP00 (0x67503030)
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+ %p4cb 00Pg (0x30305067)
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+ %p4cr 00Pg (0x30305067)
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+
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+Examples for a big-endian machine, given &(u32)0x67503030::
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+
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+ %p4ch gP00 (0x67503030)
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+ %p4cl 00Pg (0x30305067)
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+ %p4cb gP00 (0x67503030)
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+ %p4cr 00Pg (0x30305067)
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+
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Thanks
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======
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diff --git a/lib/vsprintf.c b/lib/vsprintf.c
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index 3c1853a9d1c0..31707499f90f 100644
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--- a/lib/vsprintf.c
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+++ b/lib/vsprintf.c
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@@ -1757,27 +1757,50 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc,
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char output[sizeof("0123 little-endian (0x01234567)")];
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char *p = output;
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unsigned int i;
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+ bool pix_fmt = false;
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u32 orig, val;
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- if (fmt[1] != 'c' || fmt[2] != 'c')
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+ if (fmt[1] != 'c')
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return error_string(buf, end, "(%p4?)", spec);
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if (check_pointer(&buf, end, fourcc, spec))
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return buf;
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orig = get_unaligned(fourcc);
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- val = orig & ~BIT(31);
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+ switch (fmt[2]) {
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+ case 'h':
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+ val = orig;
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+ break;
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+ case 'r':
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+ val = orig = swab32(orig);
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+ break;
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+ case 'l':
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+ val = orig = le32_to_cpu(orig);
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+ break;
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+ case 'b':
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+ val = orig = be32_to_cpu(orig);
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+ break;
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+ case 'c':
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+ /* Pixel formats are printed LSB-first */
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+ val = swab32(orig & ~BIT(31));
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+ pix_fmt = true;
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+ break;
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+ default:
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+ return error_string(buf, end, "(%p4?)", spec);
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+ }
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for (i = 0; i < sizeof(u32); i++) {
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- unsigned char c = val >> (i * 8);
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+ unsigned char c = val >> ((3 - i) * 8);
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/* Print non-control ASCII characters as-is, dot otherwise */
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*p++ = isascii(c) && isprint(c) ? c : '.';
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}
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- *p++ = ' ';
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- strcpy(p, orig & BIT(31) ? "big-endian" : "little-endian");
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- p += strlen(p);
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+ if (pix_fmt) {
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+ *p++ = ' ';
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+ strcpy(p, orig & BIT(31) ? "big-endian" : "little-endian");
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+ p += strlen(p);
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+ }
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*p++ = ' ';
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*p++ = '(';
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--
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2.34.1
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