Messages in this thread | | | Date | Tue, 19 Sep 2017 15:19:54 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH 1/2] ARM: smccc-call: Use r12 to route secure monitor calls on TI platforms |
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On Mon, Sep 18, 2017 at 03:50:04PM -0500, Andrew F. Davis wrote: > Our ROM Secure Monitor(SM) uses the value in r12 to determine which > service is being requested by an SMC call. This inline with the ARM > recommended SMC Calling Convention(SMCCC), which partitions the values > in R0 for this task, OP-TEE's SM follows the ARM recommended convention.
I can't parse this last sentence. What exactly is inline with the SMCCC?
AFAICT, the SMCCC says r12 is "The Intra-Procedure-call scratch register", which is not a paramter, service ID, etc.
> We need a way to signal that a call is for the OP-TEE SM and not for > the ROM SM in a way that is safe for the ROM SM, in case it is still > present. We do this by putting a value of 0x200 in r12 when the call > is for OP-TEE or any other ARM by modifying the SMCCC caller function.
So IIUC, you have a secure monitor which is not SMCCC compliant, but you want to use it at the same time as OP-TEE, which is SMCCC compliant.
It would be much better to have a new version of that monitor that was SMCCC compliant, and have to update the code for that, than to have to move OP-TEE away from standards compliance.
> There are four combinations of events: > > If the ROM SM is present and we make a legacy style SMC call, as we > do in early boot, the call will not have r12 set to 0x200 as these > calls go through existing mach-omap2/ SMC handlers, so all is well. > > If the ROM SM is present and we make an SMCCC style call, r12 will be > set to 0x200 and ROM SM will see this as an invalid service call and > safely return to the normal world.
So you're going to describe OP-TEE as present even when it's not!?
That's simply wrong.
> If OP-TEE is present and we make a legacy style SMC call, r12 will > not be set to 0x200, and OP-TEE will emulate the functionality that > the call is requesting.
AFAICT this means that OP-TEE completely replaces your existing monitor.
Please fix this properly. Implement SMCCC-compliant versions of those calls you wish to retain, and come up with a new binding for those. Describe that in the DT for systems which have OP-TEE providing these services.
Systems with the old monitor should have that descrbied in their DT, and not OP-TEE.
That completely removes the need to come up with a new OP-TEE binding extension, and aligns your FW for forward compatibility with future services.
Thanks, Mark.
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