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

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Date:   Tue, 19 Nov 2019 11:07:21 -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> [191119 18:51]:
> On 11/19/19 1:32 PM, Tony Lindgren wrote:
> > It would allow us to completely change over to using
> > arm_smccc_smc() and forget the custom calls.
> 
> We would need more than just the r12 quirk to replace all our custom SMC
> handlers, we would need quirks for omap_smc2 which puts process ID in r1
> and puts #0xff in r6, and omap_smc3 that uses smc #1. All of our legacy
> SMC calls also trash r4-r11, that is very non SMCCC complaint as only
> r4-r7 need be caller saved. I don't see arm_smccc_smc() working with
> legacy ROM no matter how much we hack at it :(

We would just have omap_smc2() call arm_smccc_smc() and in that
case. And omap_smc2() would still deal with saving and restoring
the registers.

Certainly the wrapper functions calling arm_smccc_smc() can deal
with r12 too if the r12-quirk version and the plain version are
never needed the same time on a booted SoC.

Are they ever needed the same time on a booted SoC or not?

> I can make OP-TEE also compatible with the r12 quirk, which is what I
> used to do. That way we didn't need to do any detection. The issue was
> that non-standard SMC calls should not go through the common SMCCC
> handler (unless you are QCOM for some reason..).

Sounds like for optee nothing must be done for r12 :)

Regards,

Tony