linux-kernel - Re: [PATCH] ARM: OMAP: Use ARM SMC Calling Convention when OP-TEE is available

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Date:   Mon, 18 Nov 2019 14:31:28 -0800
From:   Tony Lindgren <tony@...mide.com>
To:     "Andrew F. Davis" <afd@...com>
Cc:     Mark Rutland <mark.rutland@....com>, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: OMAP: Use ARM SMC Calling Convention when OP-TEE is
 available

* Andrew F. Davis <afd@...com> [191118 22:14]:
> On 11/18/19 4:57 PM, Tony Lindgren wrote:
> > Hi,
> > 
> > * Andrew F. Davis <afd@...com> [191118 08:53]:
> >> +#define OMAP_SIP_SMC_STD_CALL_VAL(func_num) \
> >> +	ARM_SMCCC_CALL_VAL(ARM_SMCCC_STD_CALL, ARM_SMCCC_SMC_32, \
> >> +	ARM_SMCCC_OWNER_SIP, (func_num))
> >> +
> >> +void omap_smc1(u32 fn, u32 arg)
> >> +{
> >> +	struct device_node *optee;
> >> +	struct arm_smccc_res res;
> >> +
> >> +	/*
> >> +	 * If this platform has OP-TEE installed we use ARM SMC calls
> >> +	 * otherwise fall back to the OMAP ROM style calls.
> >> +	 */
> >> +	optee = of_find_node_by_path("/firmware/optee");
> >> +	if (optee) {
> >> +		arm_smccc_smc(OMAP_SIP_SMC_STD_CALL_VAL(fn), arg,
> >> +			      0, 0, 0, 0, 0, 0, &res);
> >> +		WARN(res.a0, "Secure function call 0x%08x failed\n", fn);
> >> +	} else {
> >> +		_omap_smc1(fn, arg);
> >> +	}
> >> +}
> > 
> > I think we're better off just making arm_smccc_smc() work properly.
> > See cat arch/arm*/kernel/smccc-call.S.
> > 
> 
> 
> arm_smccc_smc() does work properly already, I'm using it here.

OK. I guess I don't follow then why we can't use arm_smccc_smc()
for old code.

> > If quirk handling is needed, looks like ARM_SMCCC_QUIRK_STATE_OFFS
> > can be used.
> > 
> 
> 
> Tried that [0], was NAKd. Making quirk-free SMCCC calls if OP-TEE is
> detected seems to be the suggested path forward, QCOM got a pass,
> doesn't look like we will get the same.
> 
> +Mark, in case you want to comment if this patch matches what you had in
> mind.
> 
> [0] https://www.spinics.net/lists/arm-kernel/msg607263.html

Yeah I might be missing some parts here..

> > AFAIK this should work both for optee and the current use cases.

.. as I'd like to have a solution that works for both cases using
arm_smccc_smc().

If r12 is the only issue, souds like we can just use a wrapper
for the legacy calls to call arm_smccc_smc()?

Regards,

Tony