On Thu, Jul 14, 2022 at 04:21:58AM -0600, Simon Glass wrote:
Hi Tom,
On Wed, 13 Jul 2022 at 12:09, Tom Rini trini@konsulko.com wrote:
On Wed, Jul 13, 2022 at 09:28:16AM -0600, Simon Glass wrote:
Hi Rob,
On Tue, 12 Jul 2022 at 08:11, Rob Herring robh@kernel.org wrote:
On Tue, Jul 12, 2022 at 5:04 AM Simon Glass sjg@chromium.org wrote:
Hi Ilias,
On Fri, 8 Jul 2022 at 02:24, Ilias Apalodimas ilias.apalodimas@linaro.org wrote:
Hi Simon,
[...]
> > + > > UCLASS_DRIVER(tpm) = { > > - .id = UCLASS_TPM, > > - .name = "tpm", > > - .flags = DM_UC_FLAG_SEQ_ALIAS, > > + .id = UCLASS_TPM, > > + .name = "tpm", > > + .flags = DM_UC_FLAG_SEQ_ALIAS, > > #if CONFIG_IS_ENABLED(OF_REAL) > > - .post_bind = dm_scan_fdt_dev, > > + .post_bind = dm_scan_fdt_dev, > > #endif > > + .post_probe = tpm_uclass_post_probe, > > .per_device_auto = sizeof(struct tpm_chip_priv), > > }; > > -- > > 2.25.1 > > > > The driver needs a compatible string so it can be in the device tree.
Why? I've tried to hint this on the previous iteration of the patch. The RNG here is not a *device*. The TPM is the device and you are guaranteed to have an RNG. The way to get a random number is send a special command to the TPM. So all that we should do here is leverage the fact that the TPM is already in the device tree.
And fwiw we should stick to try to stick to what the DT spec defines as much as possible. I personally don't see this as a special usecase were deviating from the spec is justified.
This is not a deviation from a spec. What spec? Also, I don't want to get into another discussion about what a device is. We can disagree on that if you like.
One reason is that U-Boot generally requires compatible strings, e.g. with of-platdata. But also we can refer to the rand device from elsewhere in the tree. I know that Linux does lots of ad-hoc device creation and doesn't really have the concept of a uclass consistently applied, but this is U-Boot.
You are letting client/OS details define your binding. Doing so doesn't result in OS agnostic bindings. Sure, it would be nice if DT nodes and drivers were always a nice clean 1:1 ratio, but h/w is messy sometimes and DT is not an abstraction layer. The general guidance on whether there are child nodes for sub-blocks is do they have their own resources in DT or are the sub-blocks reusable on multiple devices. Neither of those are the case here.
Besides, we already have TPM device bindings defined. Requiring binding changes when adding a new client/OS feature is not good practice either.
I'm not sure what to do with this, but in general the practice of implied subnodes is not friendly to U-Boot. Yet it seems like a common feature of the bindings at present, for example GPIOs.
The device tree is how U-Boot determines which random-number generator to use for a particular function. For example, for VBE, if we need to generate some random numbers we'd like to specify which device creates them. It can't just be 'use the TPM if you find one'. I'm not sure how that works in Linux?
Why can't it be "use the TPM if you find one" since a TPM is a superset of an RNG?
You mean look through the available rand devices and choose the one whose parent is a TPM?
Sure. There are lots of things you can do. But device tree is supposed to provide the tree of devices and allow such things to be configured deterministically.
No, I mean pick the TPM device because by definition it is an RNG.