On Mon, Feb 8, 2021 at 10:11 PM Sakari Ailus sakari.ailus@linux.intel.com 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.
...
+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).
...
+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).
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);
...
/* Weed out spaces */if (c == ' ')continue;
None of the existing users does that. Why?
/* 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).
*p++ = ')';*p = '\0';return string(buf, end, output, spec);+}