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

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Date:	Wed, 19 Aug 2015 17:50:09 +0100
From:	Will Deacon <will.deacon@....com>
To:	Jens Wiklander <jens.wiklander@...aro.org>
Cc:	"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>,
	Mark Rutland <Mark.Rutland@....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 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.

[...]
> diff --git a/arch/arm64/kernel/smccc-call.S b/arch/arm64/kernel/smccc-call.S
> new file mode 100644
> index 0000000..3ce7fe8
> --- /dev/null
> +++ b/arch/arm64/kernel/smccc-call.S
> @@ -0,0 +1,34 @@
> +/*
> + * Copyright (c) 2015, Linaro Limited
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License Version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + */
> +#include <linux/linkage.h>
> +
> +#define SMC_PARAM_W0_OFFS      0
> +#define SMC_PARAM_W2_OFFS      8
> +#define SMC_PARAM_W4_OFFS      16
> +#define SMC_PARAM_W6_OFFS      24
> +
> +/* void smccc_call32(struct smccc_param32 *param) */
> +ENTRY(smccc_call32)
> +       stp     x28, x30, [sp, #-16]!

Why are you saving lr?

> +       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.

Will
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