[PATCH v5 4/9] tpm: Add the RNG child device

[Sughosh Ganu]

hi Simon,

On Mon, 14 Mar 2022 at 03:53, Simon Glass <sjg at chromium.org> wrote:
>
> Hi Sughosh,
>
> On Sun, 13 Mar 2022 at 08:48, Sughosh Ganu <sughosh.ganu at linaro.org> wrote:
> >
> > The TPM device comes with the random number generator(RNG)
> > functionality which is built into the TPM device. Add logic to add the
> > RNG child device in the TPM uclass post probe callback.
> >
> > The RNG device can then be used to pass a set of random bytes to the
> > linux kernel, need for address space randomisation through the
> > EFI_RNG_PROTOCOL interface.
> >
> > Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org>
> > ---
> >
> > Changes since V4:
> >
> > * Put a check for CONFIG_TPM_RNG for binding the RNG device with it's
> >   driver in the post_probe callback instead of putting
> >   CONFIG_{SPL,TPL}_BUILD guards
> >
> >  drivers/tpm/tpm-uclass.c | 29 +++++++++++++++++++++++++----
> >  1 file changed, 25 insertions(+), 4 deletions(-)
> >
>
> This looks a lot better, please see below.
>
> > diff --git a/drivers/tpm/tpm-uclass.c b/drivers/tpm/tpm-uclass.c
> > index f67fe1019b..e1c61d26f0 100644
> > --- a/drivers/tpm/tpm-uclass.c
> > +++ b/drivers/tpm/tpm-uclass.c
> > @@ -11,10 +11,15 @@
> >  #include <log.h>
> >  #include <linux/delay.h>
> >  #include <linux/unaligned/be_byteshift.h>
> > +#include <tpm_api.h>
> >  #include <tpm-v1.h>
> >  #include <tpm-v2.h>
> >  #include "tpm_internal.h"
> >
> > +#include <dm/lists.h>
> > +
> > +#define TPM_RNG_DRV_NAME       "tpm-rng"
> > +
> >  int tpm_open(struct udevice *dev)
> >  {
> >         struct tpm_ops *ops = tpm_get_ops(dev);
> > @@ -136,12 +141,28 @@ int tpm_xfer(struct udevice *dev, const uint8_t *sendbuf, size_t send_size,
> >         return 0;
> >  }
> >
> > +static int tpm_uclass_post_probe(struct udevice *dev)
> > +{
> > +       int ret;
> > +       const char *drv = TPM_RNG_DRV_NAME;
> > +       struct udevice *child;
> > +
> > +       if (CONFIG_IS_ENABLED(TPM_RNG)) {
> > +               ret = device_bind_driver(dev, drv, "tpm-rng0", &child);
> > +               if (ret)
> > +                       return log_msg_ret("bind", ret);
> > +       }
>
> 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.

 If you want to manually bind it, please call
> device_find_first_child_by_uclass() first to make sure it isn't
> already there.

Okay

>
> Also you should bind it in the bind() method, not in probe().

Okay

>
> This is the code used for the same thing in the bootstd series:
>
> struct udevice *bdev;
> int ret;
>
> ret = device_find_first_child_by_uclass(parent, UCLASS_BOOTDEV, &bdev);
> if (ret) {
>    if (ret != -ENODEV) {
>    log_debug("Cannot access bootdev device\n");
>    return ret;
>    }
>
>    ret = bootdev_bind(parent, drv_name, "bootdev", &bdev);
>    if (ret) {
>       log_debug("Cannot create bootdev device\n");
>       return ret;
>    }
> }
>
>
> > +
> > +       return 0;
> > +}
> > +
> >  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,
>
> Should be post_bind.

Okay

-sughosh

>
> >         .per_device_auto        = sizeof(struct tpm_chip_priv),
> >  };
> > --
> > 2.25.1
> >
>
> Regards,
> Simon