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

Sakari Ailus
2020-04-02T07:18:23Z

Hi Hans,

Thank you for the review.

On Wed, Apr 01, 2020 at 04:13:51PM +0200, Hans Verkuil wrote:
> On 4/1/20 4:05 PM, 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.
> >
> > Suggested-by: Mauro Carvalho Chehab <mchehab@kernel.org>
> > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > ---
> > Documentation/core-api/printk-formats.rst | 11 +++++++++
> > lib/vsprintf.c | 29 +++++++++++++++++++++++
> > 2 files changed, 40 insertions(+)
> >
> > diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
> > index 8ebe46b1af39..b6249f513c09 100644
> > --- a/Documentation/core-api/printk-formats.rst
> > +++ b/Documentation/core-api/printk-formats.rst
> > @@ -545,6 +545,17 @@ For printing netdev_features_t.
> >
> > Passed by reference.
> >
> > +V4L2 and DRM fourcc code (pixel format)
> > +---------------------------------------
> > +
> > +::
> > +
> > + %ppf
> > +
> > +Print a 4cc code used by V4L2 or DRM.
>
> FourCC appears to be the more-or-less official name (https://en.wikipedia.org/wiki/FourCC)
>
> I would explain about the -BE suffix for bigendian fourcc variants.

Agreed, I'll address these in v2.

>
> > +
> > +Passed by reference.
> > +
> > Thanks
> > ======
> >
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > index 7c488a1ce318..b39f0ac317c5 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -1721,6 +1721,32 @@ char *netdev_bits(char *buf, char *end, const void *addr,
> > return special_hex_number(buf, end, num, size);
> > }
> >
> > +static noinline_for_stack
> > +char *pixel_format_string(char *buf, char *end, const u32 *fourcc,
> > + struct printf_spec spec, const char *fmt)
> > +{
> > + char ch[2] = { 0 };
>
> This can just be '{ };'

As Andy, I also do prefer { 0 }.

>
> > + unsigned int i;
> > +
> > + if (check_pointer(&buf, end, fourcc, spec))
> > + return buf;
> > +
> > + switch (fmt[1]) {
> > + case 'f':
> > + for (i = 0; i < sizeof(*fourcc); i++) {
> > + ch[0] = *fourcc >> (i << 3);
>
> You need to AND with 0x7f, otherwise a big endian fourcc (bit 31 is set)
> will look wrong. Also, each character is standard 7 bit ascii, bit 7 isn't
> used except to indicate a BE variant.

Good point, will fix for v2.

>
> > + buf = string(buf, end, ch, spec);
> > + }
> > +
> > + if (*fourcc & BIT(31))
> > + buf = string(buf, end, "-BE", spec);
> > +
> > + return buf;
> > + default:
> > + return error_string(buf, end, "(%pp?)", spec);
> > + }
> > +}
> > +
> > static noinline_for_stack
> > char *address_val(char *buf, char *end, const void *addr,
> > struct printf_spec spec, const char *fmt)
> > @@ -2131,6 +2157,7 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
> > * correctness of the format string and va_list arguments.
> > * - 'K' For a kernel pointer that should be hidden from unprivileged users
> > * - 'NF' For a netdev_features_t
> > + * - 'pf' V4L2 or DRM pixel format.
>
> I'd say 'FourCC format' instead of 'pixel format'.

Will fix.

--
Regards,

Sakari Ailus