Re: [PATCH v2 1/1] lib/vsprintf: Add support for printing V4L2 and DRM fourccs

On Fri, Apr 03, 2020 at 12:11:56PM +0300, Sakari Ailus wrote:

Add a printk modifier %ppf (for pixel format) for printing V4L2 and DRM pixel formats denoted by 4ccs. The 4cc encoding is the same for both so the same implementation can be used.

...

+static noinline_for_stack +char *fourcc_string(char *buf, char *end, const u32 *fourcc,

•     struct printf_spec spec, const char *fmt)
  

+{

+#define FOURCC_STRING_BE "-BE"

• char s[sizeof(*fourcc) + sizeof(FOURCC_STRING_BE)] = { 0 };

I guess it makes it too complicated.

char s[8];

• if (check_pointer(&buf, end, fourcc, spec))

• return buf;
  

• if (fmt[1] != 'c' || fmt[2] != 'c')

• return error_string(buf, end, "(%p4?)", spec);
  

• put_unaligned_le32(*fourcc & ~BIT(31), s);

Can you elaborate what the difference in output with this bit set over cleared? I.o.w. why don't we need to put it as BE and for LE case addd "-LE"?

• if (*fourcc & BIT(31))

• strscpy(s + sizeof(*fourcc), FOURCC_STRING_BE,
  

• 	sizeof(FOURCC_STRING_BE));
  

We know the size, and we may put '\0' as well if (*fourcc & BIT(31)) strscpy(&s[4], "-BE", sizeof("-BE")); else strscpy(&s[4], "", sizeof(""));

• return string(buf, end, s, spec);

+}