On Thu, Aug 20, 2015 at 12:37:29PM +0100, Jens Wiklander wrote:

On Wed, Aug 19, 2015 at 05:50:09PM +0100, Will Deacon wrote:

quoted

On Wed, Aug 19, 2015 at 09:40:25AM +0100, Jens Wiklander wrote:

quoted

Adds helpers to do SMC based on ARM SMC Calling Convention.
CONFIG_HAVE_SMCCC is enabled for architectures that may support
the SMC instruction. It's the responsibility of the caller to
know if the SMC instruction is supported by the platform.

[...]

quoted

quoted

+       mov     x28, x0
+       ldp     w0, w1, [x28, #SMC_PARAM_W0_OFFS]
+       ldp     w2, w3, [x28, #SMC_PARAM_W2_OFFS]
+       ldp     w4, w5, [x28, #SMC_PARAM_W4_OFFS]
+       ldp     w6, w7, [x28, #SMC_PARAM_W6_OFFS]
+       smc     #0
+       stp     w0, w1, [x28, #SMC_PARAM_W0_OFFS]
+       stp     w2, w3, [x28, #SMC_PARAM_W2_OFFS]
+       ldp     x28, x30, [sp], #16
+       ret
+ENDPROC(smccc_call32)

Could we deal with this like we do for PSCI instead? (see
__invoke_psci_fn_smc). We could also then rename psci-call.S to fw-call.S
and stick this in there too.

I assume you're referring to when to use "hvc" and "smc".

I assume he's on about passing the values in registers rather than a struct.

From the looks of the SMC Calling Convention documentation, it's valid to have

return values in registers r0-r3, which necessitates the use of a struct (at
least for the return values).

Thanks,
Mark.