[PATCH v3 6/7] firmware: arm_ffa: Setup in-kernel users of FFA partitions

[Jens Wiklander]

On Wed, Jan 13, 2021 at 10:44 AM Sudeep Holla <sudeep.holla at arm.com> wrote:
[...]
> > > > +static int ffa_partition_probe(const char *uuid_str,
> > > > +                              struct ffa_partition_info *buffer)
> > > > +{
> > > > +       int count;
> > > > +       uuid_t uuid;
> > > > +       u32 uuid0_4[4] = { 0 };
> > > > +
> > > > +       if (uuid_parse(uuid_str, &uuid)) {
> > > > +               pr_err("invalid uuid (%s)\n", uuid_str);
> > > > +               return -ENODEV;
> > > > +       }
> > > > +
> > > > +       export_uuid((u8 *)uuid0_4, &uuid);
> > > > +       count = __ffa_partition_info_get(uuid0_4[0], uuid0_4[1], uuid0_4[2],
> > > > +                                        uuid0_4[3], &buffer);
> > Wrong byte order?
> > According to section 5.3 of the SMCCC, UUIDs are returned as a single
> > 128-bit value using the SMC32 calling convention. This value is mapped
> > to argument registers x0-x3 on AArch64 (resp. r0-r3 on AArch32). x0
> > for example shall hold bytes 0 to 3, with byte 0 in the low-order
> > bits.
> >
>
> I need to spend some time to understand the concern here. Initially I agreed
> with your analysis and then a quick review make be realise it is all OK.
> I need to check if my understanding is correct again. I thought I will
> take example and check here itself.
>
> UUID: "fd02c9da-306c-48c7-a49c-bbd827ae86ee"
>
> UUID[0]   UUID[1]  UUID[2]  UUID[3] (referring uuid0_4 above)
> dac902fd c7486c30 d8bb9ca4 ee86ae27
>
> It seems correct as per SMCCC convention to me, or am I missing something
> obvious ?

In this example I'd expect the first register to hold 0xfd02c9da
regardless of the byte order of the machine. If there is a different
byte order in the receiver it will still be received as 0xfd02c9da.
That's how I've understood the specification.

Cheers,
Jens