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. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
