Hi Simon, A bit late on this, but at least I found it...
On Wed, Mar 16, 2022 at 10:15:34AM +1300, Simon Glass wrote: > Hi Ilias, > > On Tue, 15 Mar 2022 at 00:34, Ilias Apalodimas > <ilias.apalodi...@linaro.org> wrote: > > > > Hi Simon, > > > > On Mon, 14 Mar 2022 at 20:24, Simon Glass <s...@chromium.org> wrote: > > > > > > > [...] > > > > > > > > + } > > > > > > > > > > This really should be in the device tree so what you are doing here is > > > > > quite strange. > > > > > > > > Like I had mentioned in my earlier emails, the TPM device has a > > > > builtin RNG functionality, which is non-optional. So I don't > > > > understand why we need to use a device tree subnode here. Whether the > > > > device is being bound to the parent is being controlled by the TPM_RNG > > > > config that you asked me to put in my previous version, which I am > > > > doing. > > > > > > See how PMICs work, for example. We have GPIOs, regulators and > > > suchlike in the PMIC and we add subnodes for them in the DT. It is > > > just how it is done. > > > > > > Driver model is designed to automatically bind devices based on the > > > device tree. There are cases where it is necessary to manually bind > > > things, but we mustn't prevent people from doing it 'properly'. > > > > There's a small difference here though. The RNG is not a device. The > > TPM is the device and an encoded command to that device returns a > > random number. There's no binding initiating etc. > > A device is just something with a struct udevice, so I don't see the > random number generator as anything different from another device. We > might have a white-noise generator which produces random numbers. Just > because the feature is packaged inside a single chip doesn't make it > any less a device. Just like the PMIC. > > > > > > > > > Finally, I know you keep saying that random numbers are only needed in > > > U-Boot proper, but if I want a random number in SPL, it may not work, > > > since device_bind() is often not available, for code-size reasons. > > > > And the entire tpm framework will fit? > > Yes. For verified boot it has to, since you cannot init RAM until you > have selected your A/B/recovery image. If so I still don't see why this needs a DT node. If, as you say, the TPM framework fits in then you just call tpm_get_random(). Getting the RNG is a series of commands to the TPM. Sou you'll need the TPM lib in SPL regardless. > > > > > > > > > So that is why I say that what you are doing is quite strange. Perhaps > > > you are coming from a different project, which does things > > > differently. > > > > I don't personally find it strange. The device is already described > > in the DTS and I don't see a strong reason to deviate for the upstream > > version again. > > Linux tends to rely a lot more on manually adding devices. It can have > a pretty dramatic bloating effect on code size in U-Boot. > > Anyway, so long as we can detect an existing device, as I explained > below, it is fine to manually add it when it is missing. > You can detect a TPM. Once you add that tpm then you *know* you can get an RNG [...] Regards /Ilias
