[PATCH v4] tee: optee: rework TA bus scanning code

[Ilias Apalodimas]

Hi Simon,

On Thu, 8 Sept 2022 at 00:11, Simon Glass <sjg at chromium.org> wrote:
>
> Hi Ilias,
>
> On Tue, 6 Sept 2022 at 15:23, Ilias Apalodimas
> <ilias.apalodimas at linaro.org> wrote:
> >
> > Hi Simon,
> >
> > On Tue, Sep 06, 2022 at 03:18:28PM -0600, Simon Glass wrote:
> > > Hi,
> > >
> > > On Tue, 6 Sept 2022 at 03:37, Ilias Apalodimas
> > > <ilias.apalodimas at linaro.org> wrote:
> > > >
> > > > Late versions of OP-TEE support a pseudo bus.  TAs that behave as
> > > > hardware blocks (e.g TPM, RNG etc) present themselves on a bus which we can
> > > > scan.  Unfortunately U-Boot doesn't support that yet. It's worth noting
> > > > that we already have a workaround for RNG.  The details are in
> > > > commit 70812bb83da6 ("tee: optee: bind rng optee driver")
> > > >
> > > > So let's add a list of devices based on U-Boot Kconfig options that we will
> > > > scan until we properly implement the tee-bus functionality.
> > > >
> > > > While at it change the behaviour of the tee core itself wrt to device
> > > > binding.  If some device binding fails, print a warning instead of
> > > > disabling OP-TEE.
> > > >
> > > > Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> > > > Reviewed-by: Jens Wiklander <jens.wiklander at linaro.org>
> > > > Reviewed-by: Etienne Carriere <etienne.carriere at linaro.org>
> > > > ---
> > > > Changes since v3:
> > > > - Use NULL instead of a child ptr on device_bind_driver(), since it's not
> > > > really needed
> > > > - Changed the style of the optee_bus_probe[] definition to
> > > >   {.drv_name = xxx, .dev_name = yyy }
> > > >
> > > > Changes since v2:
> > > > - Fixed typo on driver name ftpm-tee -> ftpm_tee
> > > >
> > > > Changes since v1:
> > > > - remove a macro and use ARRAY_SIZE directly
> > > >  drivers/tee/optee/core.c | 24 +++++++++++++++++++-----
> > > >  1 file changed, 19 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/drivers/tee/optee/core.c b/drivers/tee/optee/core.c
> > > > index a89d62aaf0b3..c201a4635e6b 100644
> > > > --- a/drivers/tee/optee/core.c
> > > > +++ b/drivers/tee/optee/core.c
> > > > @@ -31,6 +31,18 @@ struct optee_pdata {
> > > >         optee_invoke_fn *invoke_fn;
> > > >  };
> > > >
> > > > +static const struct {
> > > > +       const char *drv_name;
> > > > +       const char *dev_name;
> > > > +} optee_bus_probe[] = {
> > > > +#ifdef CONFIG_RNG_OPTEE
> > > > +       { .drv_name = "optee-rng", .dev_name = "optee-rng" },
> > > > +#endif
> > > > +#ifdef CONFIG_TPM2_FTPM_TEE
> > > > +       { .drv_name = "ftpm_tee", .dev_name = "ftpm_tee" },
> > > > +#endif
> > > > +};
> > > > +
> > > >  struct rpc_param {
> > > >         u32     a0;
> > > >         u32     a1;
> > > > @@ -642,8 +654,7 @@ static int optee_probe(struct udevice *dev)
> > > >  {
> > > >         struct optee_pdata *pdata = dev_get_plat(dev);
> > > >         u32 sec_caps;
> > > > -       struct udevice *child;
> > > > -       int ret;
> > > > +       int ret, i;
> > > >
> > > >         if (!is_optee_api(pdata->invoke_fn)) {
> > > >                 dev_err(dev, "OP-TEE api uid mismatch\n");
> > > > @@ -672,10 +683,13 @@ static int optee_probe(struct udevice *dev)
> > > >          * in U-Boot, the discovery of TA on the TEE bus is not supported:
> > > >          * only bind the drivers associated to the supported OP-TEE TA
> > > >          */
> > > > -       if (IS_ENABLED(CONFIG_RNG_OPTEE)) {
> > > > -               ret = device_bind_driver(dev, "optee-rng", "optee-rng", &child);
> > > > +
> > > > +       for (i = 0; i < ARRAY_SIZE(optee_bus_probe); i++) {
> > > > +               ret = device_bind_driver(dev, optee_bus_probe[i].drv_name,
> > > > +                                        optee_bus_probe[i].dev_name, NULL);
> > > >                 if (ret)
> > > > -                       return ret;
> > > > +                       dev_warn(dev, "Failed to bind device %s\n",
> > > > +                                optee_bus_probe[i].dev_name);
> > >
> > > Please add device tree nodes for these and all this code can go away.
> >
> > That's the exact opposite of what the commit message describes.  OP-TEE
> > supports a scannable bus ifor TAs that  behave like hardware blocks and
> > doesn't need a DT entry.  Since it's really the TAs compilation decision
> > to support that or not having them as a DT node is not always the right
> > choice.
>
> This is continuing the perversion of how things are supposed to work
> in driver model.

Which is not the only thing we need to keep in mind though.

>
> We need to talk about this because it is simply the wrong way to be
> approaching this.

This is already part of other software components though, e.g it's
already in the kernel.  So I don't think it's the wrong approach.

> There is nothing wrong with putting things in the DT
> and this is how U-Boot works. For now, please create a binding and get
> it reviewed. You don't need all the internal objects but you do need
> an OP-TEE driver and node, as we have with PCI.

Some things *are* working without a DT entry.  You had similar
concerns on FF-A (where you requested a DT node again) and people gave
the exact same response.  As long as a bus is scanable in any way,
it's preferable to than adding a DT entry.  Moreover this code does
not prevent anyone from adding a DT entry.

To make things even worse if the TA is compiled as 'scanable' and has
a DT entry, it might cause issues down the road when being probed by
the kernel.  So really this is just a patch that makes u-boot behave
and plug in properly to the rest of the ecosystem

Thanks
/Ilias
>
> Regards,
> Simon