On Fri, Mar 26, 2021 at 12:18:50PM +0000, Mark Rutland wrote:

On Thu, Mar 25, 2021 at 02:41:13PM +0000, Mark Rutland wrote:

quoted

Hi Sudeep,

On Thu, Mar 25, 2021 at 02:32:50PM +0000, Sudeep Holla wrote:

quoted

SMCCC v1.2 allows x8-x17 to be used as parameter registers and x4—x17
to be used as result registers in SMC64/HVC64. Arm Firmware Framework
for Armv8-A specification makes use of x0-x7 as parameter and result
registers.

Current SMCCC interface in the kernel just use x0-x7 as parameter and
x0-x3 as result registers. Let us add new interface to support x0-x7
as parameter and result registers. This can be extended to include
x8-x17 when there are users for the same.

Michael Kelley is also looking at using SMCCCv1.2, and on his HyperV
thread I'd suggested we should deal with the whole set of SMCCCv1.2
registers now to avoid future churn in this area (using struct both for
the arguments and return values).

How painful would it be to extend this patch to do that?

I *think* the major change with this would be making the interfaces:

void arm_smccc_1_2_{hvc,smc}(struct arm_smccc_1_2_args *args,
			     struct arm_smccc_1_2_res *res);

... and callers manipulating the structs directly, with arm64 having
more fields, e.g.

// arm64
struct arm_smccc_1_2_args {
	unsigned long a1;
	...
	unsigned long a17;
}

struct arm_smccc_1_2_res {
	unsigned long a0;
	...
	unsigned long a17;
}

// arm
struct arm_smccc_1_2_args {
	unsigned long a1;
	...
	unsigned long a7;
}

struct arm_smccc_1_2_res {
	unsigned long a0;
	...
	unsigned long a7;
}

I think that can be hidden in the FF-A wrappers, so that doesn't need to
be what FF-A drivers see. Does that sound plausible, or is that painful?

Sounds possible, will give it a try.

quoted

quoted

+  DEFINE(ARM_SMCCC_V1_2_RES_X0_OFFS,	offsetof(struct arm_smccc_v1_2_res, a0));

As a general nit, for consistency with the existing arm_smccc_1_1 code,
could we please drop the 'V' in these names, and use `ARM_SMCCC_1_2` or
`arm_smccc_1_2` ?

Sure, makes sense.

FWIW, other than the above comments, this all looks good to me

Thanks.

--
Regards,
Sudeep