Re: [PATCH v1 2/8] firmware: arm_rmm: Add VSMMU commands and fields

[Jason Gunthorpe]

On Thu, Oct 29, 2026 at 10:05:05AM +0000, Shameer Kolothum Thodi wrote:
> > On Wed, Oct 28, 2026 at 09:35:09AM -0300, Jason Gunthorpe wrote:
> > > On Wed, Oct 28, 2026 at 09:49:53AM +0000, Shameer Kolothum Thodi
> > wrote:
> > > > > +static inline unsigned long rsi_arch_dev_activate(phys_addr_t base,
> > > > > +						  unsigned long dev_type)
> > > > > +{
> > > > > +	struct arm_smccc_res res;
> > > > > +
> > > > > +	arm_smccc_1_1_invoke(SMC_RSI_ARCH_DEV_ACTIVATE, base,
> > > > > dev_type, &res);
> > > >
> > > > These calls leave unused input registers unspecified, whereas
> > > > DEN0137 bet3 B1.2 marks them SBZ. Could we explicitly zero them?
> > > >
> > > > "On calling an RMI or RSI command, any of X1- X16 which are not
> > > >  specified as input values in the command definition SBZ"
> > >
> > > That seems too broad, Linux doesn't even support the x8-x16 inputs in
> > > the macros. I think the spec has errd here.
> > >
> > > Requiring zeroing of x0-x7 is sort of reasonable. Any future use of
> > > x8-x16 (including outputs) should require a direct opt in of the OS to
> > > indicate it supports this bank of registers.
> > >
> > > Otherwise you probably need a new macro helper for this protocol..
> > 
> > We could probably replace it with:
> > 	arm_smccc_smc(SMC_RSI_ARCH_DEV_ACTIVATE, base, dev_type, 0,
> > 0, 0, 0, 0,
> > 		      &res);
> > 
> > This should specify those unused inputs.
> 
> Or we could use arm_smccc_1_2_smc() with zero initialized registers, as
> rsi_attestation_token_init() does. I think that would cover X8-X16 too.

Yeah, that seems to be the right thing to do.

> But other RSI wrappers don't do that consistently, so it's fine either
> way, I guess.

Seems like a bug, with the spec being specific here it should be
fixed.

Jason