RE: [PATCH v3 1/5] event/opdl: fix non-constant compile time assertion

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> Sent: Wednesday, 17 January 2024 10.27
> 
> On Wed, Jan 17, 2024 at 10:58:12AM +0300, Andrew Rybchenko wrote:
> > On 1/16/24 21:41, Stephen Hemminger wrote:
> > > RTE_BUILD_BUG_ON() was being used with a non-constant value.
> > > The inline function rte_is_power_of_2() is not constant since
> > > inline expansion happens later in the compile process.
> > > Replace it with macro which will be constant.
> > >
> > > Fixes: 4236ce9bf5bf ("event/opdl: add OPDL ring infrastructure
> library")
> > > Cc: liang.j.ma@intel.com
> > > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> > > Acked-by: Bruce Richardson <bruce.richardson@intel.com>
> > > Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> > > ---
> > >   drivers/event/opdl/opdl_ring.c | 5 ++++-
> > >   1 file changed, 4 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/event/opdl/opdl_ring.c
> b/drivers/event/opdl/opdl_ring.c
> > > index 69392b56bbec..24e0bbe3222d 100644
> > > --- a/drivers/event/opdl/opdl_ring.c
> > > +++ b/drivers/event/opdl/opdl_ring.c
> > > @@ -31,6 +31,9 @@
> > >   #define OPDL_OPA_MASK    (0xFF)
> > >   #define OPDL_OPA_OFFSET  (0x38)
> > > +/* Equivalent to rte_is_power_of_2() but as macro. */
> > > +#define IS_POWER_OF_2(x) (((x) & ((x) - 1)) == 0)
> >
> > IMHO adding it in specific driver is a wrong direction. I'm afraid it
> > will result in duplication of such macros in code base without clear
> > reason why.
> >
> > May be it is better to add it with a proper name to EAL?
> >
> +1
> Even if it's a lower-case name, lets make it a macro in EAL so we can
> use
> it everywhere in asserts.

Here's a thought... we could introduce a new code convention for this purpose. E.g. either:

1. Macros in lower case are guaranteed to access each parameter exactly once (and might not be usable for static_assert; they somewhat resemble inline functions), and
macros in upper case may access parameters any number of times (and must be usable for static_assert).

Or:

2. Macros that access any parameter zero or multiple times must have their name postfixed _UNSAFE (or some other word).