Messages in this thread | | | Date | Tue, 26 Jul 2022 19:01:28 +0200 | Subject | Re: [PATCH 4/4] dt-bindings: firmware: Add Qualcomm UEFI Secure Application client | From | Maximilian Luz <> |
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On 7/26/22 17:41, Sudeep Holla wrote: > On Tue, Jul 26, 2022 at 05:15:41PM +0200, Maximilian Luz wrote: >> >> So ultimately I think it's better to add a DT entry for it. > > I disagree for the reason that once you discover more apps running on the > secure side, you want to add more entries and update DT on the platform > every time you discover some new firmware entity and you wish to interact > with it from the non-secure side.
Just as you'll have to add a driver to the kernel and update whatever is probing the TrEE interface and add those strings to that interface. If you then start doing SoC-specific lists, I think you'd be pretty much re-implementing a DT in the kernel driver...
I don't quite understand why this is a problem. I think per device, there's a reasonably limited set of apps that we would want to interact with from the kernel. And for one single device, that set doesn't change over time. So what's the difference to, say, an I2C device?
> As along as get this application ID can handle any random name, I prefer > to use that as the discover mechanism and not have this DT.
Apart from the above, some apps must also be loaded from the system. And those you can't detect: If an app isn't running, it doesn't have an ID (uefisecapp and the tpm app are loaded by the firmware at boot). Those are mostly vendor-specific things as far as I can tell, or HDCP stuff. So you'd need to specify those as firmware somehow, and since (as far as I can tell) those are signed specifically by/for that vendor and potentially device (similar to the GPU zap shader or remoteproc firmware), you'll need to use per-device paths.
That means you either hard-code them in the driver and have a compatible per model, do DMI matching, or something similar (again, essentially baking DTs into the kernel driver...), or just store them in the DT (like we already do for GPU/remoteprocs). While you could hard-code some known loaded-by-firmware apps and use the DT for others, I think we should keep everything in the same place.
Windows uses a hard-coded list of supported apps in the driver (to specify which apps the driver supports) and in addition to that uses Registry entries (added via .inf files) to specify which app is supposed to be present on the device and, for apps that need to be loaded, where the firmware to be loaded is stored. It only ever attempts to connect to those apps that are marked present in the registry. Which, again, may be model/vendor specific.
And this is another reason I'm hesitant to use that function: Windows doesn't use it in this way and that I don't know whether there can be any subtle breakage or unexpected behavior if we use the function like that (i.e., who's to say some broken firmware returns "app is present" but the app is broken?).
Regards, Max
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