linux-kernel - Re: [PATCH v5 1/5] arm/arm64: add smccc ARCH32

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Date:	Thu, 20 Aug 2015 22:30:29 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Jens Wiklander <jens.wiklander@...aro.org>
Cc:	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Kees Cook <keescook@...omium.org>,
	"valentin.manea@...wei.com" <valentin.manea@...wei.com>,
	"javier@...igon.com" <javier@...igon.com>,
	"emmanuel.michel@...com" <emmanuel.michel@...com>,
	Michal Simek <michal.simek@...inx.com>,
	"jean-michel.delorme@...com" <jean-michel.delorme@...com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v5 1/5] arm/arm64: add smccc ARCH32

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

[...]

> > > +       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.

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