On Mon, Feb 8, 2021 at 10:11 PM Sakari Ailus
[off-list ref] wrote:
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.
Thank you for an update with the examples how current users will be
converted. Below review is based on the users I had seen so far and
assumptions made in this code. I see that it's tagged by maintainers,
but I can't help to comment again on this. In any case the decision is
up to them.
...
quoted hunk ↗ jump to hunk
+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)
This misses examples of the (strange) escaping cases and wiped
whitespaces to make sure everybody understands that 'D 12' will be the
same as 'D1 2' (side note: which I disagree on, perhaps something
should be added into documentation why).
...
quoted hunk ↗ jump to hunk
+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)")];
Do we have any evidence / document / standard that the above format is
what people would find good? From existing practices (I consider other
printings elsewhere and users in this series) I find '(xx)' form for
hex numbers is weird. The standard practice is to use \xHH (without
parentheses).
quoted hunk ↗ jump to hunk
+ char *p = output;
+ unsigned int i;
+ u32 val;
+
+ if (fmt[1] != 'c' || fmt[2] != 'c')
+ return error_string(buf, 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);
...
quoted hunk ↗ jump to hunk
+ /* Weed out spaces */
+ if (c == ' ')
+ continue;
None of the existing users does that. Why?
quoted hunk ↗ jump to hunk
+ /* 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++ = '(';
+ p = special_hex_number(p, output + sizeof(output) - 2, *fourcc,
+ sizeof(u32));
This is perfectly one line (in this file we have even longer lines).
quoted hunk ↗ jump to hunk
+ *p++ = ')';
+ *p = '\0';
+
+ return string(buf, end, output, spec);
+}
--
With Best Regards,
Andy Shevchenko