Re: [PATCH v6 3/4] firmware: smccc: arm-cca-guest: Bind the TSM provider to an SMCCC device

[Sudeep Holla]

On Thu, Jun 04, 2026 at 06:56:28PM +0530, Aneesh Kumar K.V wrote:
> Sudeep Holla <sudeep.holla@xxxxxxxxxx> writes:
> 
> ...
> 
> > +static const struct smccc_device_info smccc_devices[] __initconst = {
> > +       {
> > +               .func_id        = ARM_SMCCC_TRNG_VERSION,
> > +               .requires_smc   = false,
> > +               .min_return     = ARM_SMCCC_TRNG_MIN_VERSION,
> > +               .device_name    = "arm-smccc-trng",
> > +       },
> > +};
> > +
> > +static bool __init
> > +smccc_probe_smccc_device(const struct smccc_device_info *smccc_dev)
> > +{
> > +       struct arm_smccc_res res;
> > +       unsigned long ret;
> > +
> > +       if (!IS_ENABLED(CONFIG_ARM64))
> > +               return false;
> > +
> > +       if (smccc_conduit == SMCCC_CONDUIT_NONE)
> > +               return false;
> > +
> > +       if (smccc_dev->requires_smc && smccc_conduit != SMCCC_CONDUIT_SMC)
> > +               return false;
> > +
> > +       arm_smccc_1_1_invoke(smccc_dev->func_id, &res);
> > +       ret = res.a0;
> > +
> > +       if ((s32)ret < 0)
> > +               return false;
> > +
> > +       return ret >= smccc_dev->min_return;
> > +}
> > +
> >
> 
> I am not sure we want the check to be as simple as ret < 0. Some
> function IDs may return input errors based on the supplied arguments
> (for example, RMI_ERROR_INPUT). In those cases, we would likely want
> this to be handled via a callback.
> 

As I mentioned in response to Suzuki, we can defer that to probe of
that device. If *_VERSION, succeeds SMCCC core can add that device and
leave the rest to the core keeping the core and bus layer simple IMO.

> We also want to use conditional compilation for some function IDs.
> Given the callback approach and the #ifdefs, I wonder whether what we
> currently have is actually simpler and more flexible.”
> 

I was trying to avoid conditional compilation altogether and hence the
reason for keeping it as simple as possible. Also IS_ENABLED(CONFIG_ARM64)
in above snippet must come as some condition to this generic probe.

Adding any more logic or callback defeats the bus idea here if we need
to rely/depend on multiple conditional compilation or callbacks IMO.

Let's find see if it can work with what we are adding now and may add in
near future and then decide.

-- 
Regards,
Sudeep