On Fri, Jul 23, 2021 at 05:53:15PM +0200, Clément Léger wrote: > Mark Brown <broonie@xxxxxxxxxx> a écrit : > > I can't see any SMC specification for this interface? Frankly I have > > some very substantial concerns about the use case for this over > > exposing the functionality of whatever device the SMC is gating > > access to through SMC interfaces specific to that functionality. > This would require to modify drivers to check if the access should be > done using SMCs, parse the device tree to find appropriate SMC ids for > each functionality, add dependencies in KConfig on > HAVE_ARM_SMCCC_DISCOVERY, and do SMC calls instead of regmap access. > I'm not saying this is not the way to go but this is clearly more > intrusive than keeping the existing syscon support. You're not doing this at the syscon level, you're doing this at the regmap level. Any user of this code is going to have to be modified to use the SMCCC regmap and discover the relevant SMCCC interfaces no matter what, but by having it we're saying that that's a sensible and reasonable thing to do and encouraging implementations as a result. Device specific regmap interfaces do not require adding anything to the core, there's the reg_read() and reg_write() callbacks for this, if there is a sensible use case for this at the syscon level and only the syscon level (but I really do strongly question if it's a good idea at all) then you can use those without adding a generic interface for defining SMCCC conduits as regmaps. TBH what's being added to the regmap core is so trival that I don't see what we'd be gaining anyway even if this was widely used, it's not helping with the SMCCC enumeration side at all. > > Exposing raw access to a (presumed?) subset of whatever device > > functionality feels like the wrong abstraction level to be working at > > and like an invitation to system integrators to do things that are > > going to get them into trouble down the line. > Indeed, access is reduced to a subset of registers offset which are > checked by the TEE. I really think it would be clearer and safer to have the TEE expose specific operations that encode the intent of whatever it is trying to accomplish rather than just expose the register map and then audit the operations that are going on in the register map after the fact. It seems like it's going to be more error prone to do things this way, especially as this starts getting used as a generic pipe for exposing things and things get built up - as well as auditing concerns if any problems are identified it's going to be harder to track the intent of what the non-secure world is doing.
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