Hi Sughosh, On Mon, 21 Mar 2022 at 00:01, Sughosh Ganu <sughosh.g...@linaro.org> wrote: > > hi Simon, > > On Wed, 16 Mar 2022 at 02:45, Simon Glass <s...@chromium.org> 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. > > > > > > > > > > > > > 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. > > Just so that I understand what you are saying, do you want support for > both approaches. Meaning, using device tree when the rng node is > described in the device tree, and otherwise using the manual device > binding when the device tree node is absent. Do I understand this > right?
Yes that's what we normally do in U-Boot. Regards, Simon
