Re: [RFC PATCH] pps: Increase PPS_MAX_SOURCES value.

[Rodolfo Giometti]

On 08/06/23 00:07, Charlie Johnston wrote:
> On 6/7/23 02:33, Rodolfo Giometti wrote:
> > On 05/06/23 22:31, Charlie Johnston wrote:
> > > For consistency with what ptp uses for minors, this
> > > change sets PPS_MAX_SOURCES to MINORMASK + 1.
> > >
> > > The PPS_MAX_SOURCES value is currently set to 16. In
> > > some cases this was not sufficient for a system. For
> > > example, a system with multiple (4+) PCIe cards each
> > > with 4 PTP-capable ethernet interfaces could run out
> > > of the available PPS major:minors if each interface
> > > registers a PPS source.
> > >
> > > Signed-off-by: Charlie Johnston <charlie.johnston@xxxxxx>
> > > ---
> > >    include/uapi/linux/pps.h | 2 +-
> > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/include/uapi/linux/pps.h b/include/uapi/linux/pps.h
> > > index 009ebcd8ced5..85f472330da8 100644
> > > --- a/include/uapi/linux/pps.h
> > > +++ b/include/uapi/linux/pps.h
> > > @@ -26,7 +26,7 @@
> > >    #include <linux/types.h>
> > >      #define PPS_VERSION        "5.3.6"
> > > -#define PPS_MAX_SOURCES        16        /* should be enough... */
> > > +#define PPS_MAX_SOURCES        (MINORMASK + 1)
> > >      /* Implementation note: the logical states ``assert'' and ``clear''
> > >     * are implemented in terms of the chip register, i.e. ``assert''
> >
> > I have just one question: are you sure that it's safe to call idr_alloc(..., 0, (MINORMASK + 1), ...)?
> >
> > Ciao,
> >
> > Rodolfo
>
> Thanks for taking a look!
>
> My understanding is that idr_alloc(..., start, end, ...) can take any end value up to INT_MAX. It also handles any values <= 0 by treating them as equal to INT_MAX + 1 since the end value is non-inclusive. I can't think of any reason using MINORMASK + 1 here would be an issue since it's much less than the maximum value idr_alloc() allows.
>
> A number of drivers (e.g. ptp) just explicitly use a start and end value of 0, but I don't think that change would fit here.

I see and maybe I should replace the usage of idr_*() with ida_*() as PTP does...

However the right-thing(TM) to do here should be dropping PPS_MAX_SOURCES at all!

Let me go deeper in this issue. I'm going to produce a patch set in next days. 
Have you any chances to test it?

Ciao,

Rodolfo

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