[PATCH v4 4/8] tpm: Add the RNG child device

[Sughosh Ganu]

hi Simon,

On Sat, 12 Mar 2022 at 08:14, Simon Glass <sjg at chromium.org> wrote:
>
> Hi Sughosh,
>
> On Wed, 9 Mar 2022 at 05:28, 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 V3:
> >
> > * Build the RNG child addition only for the u-boot proper stage using
> >   the CONFIG_{SPL,TPL}_BUILD guards instead of CONFIG_TPM config which
> >   gets included in all stages.
> > * Remove the child_pre_probe callback which was starting the TPM
> >   device based on review from Simon.
> >
> >  drivers/tpm/tpm-uclass.c | 40 ++++++++++++++++++++++++++++++++++++----
> >  lib/Kconfig              |  1 +
> >  2 files changed, 37 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/tpm/tpm-uclass.c b/drivers/tpm/tpm-uclass.c
> > index f67fe1019b..241ed01e68 100644
> > --- a/drivers/tpm/tpm-uclass.c
> > +++ b/drivers/tpm/tpm-uclass.c
> > @@ -11,10 +11,16 @@
> >  #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_RNG1_DRV_NAME      "tpm1-rng"
> > +#define TPM_RNG2_DRV_NAME      "tpm2-rng"
> > +
> >  int tpm_open(struct udevice *dev)
> >  {
> >         struct tpm_ops *ops = tpm_get_ops(dev);
> > @@ -136,12 +142,38 @@ int tpm_xfer(struct udevice *dev, const uint8_t *sendbuf, size_t send_size,
> >         return 0;
> >  }
> >
> > +#if !IS_ENABLED(CONFIG_SPL_BUILD) && !IS_ENABLED(CONFIG_TPL_BUILD)
>
> Drop that

Okay. Btw, putting the check for the config symbol as you suggest
below does add some size to the SPL/TPL code. But that is theoretical,
since we currently do not enable CONFIG_{SPL,TPL}_TPM.

>
> > +static int tpm_uclass_post_probe(struct udevice *dev)
> > +{
> > +       int ret;
> > +       const char *drv = tpm_is_v1(dev) ?
> > +               TPM_RNG1_DRV_NAME : TPM_RNG2_DRV_NAME;
> > +       struct udevice *child;
> > +
>
> if (CONFIG_IS_ENABLED(TPM_RNG))  {

Okay

>
> > +       ret = device_bind_driver(dev, drv, "tpm-rng0", &child);
> > +       if (ret == -ENOENT) {
> > +               log_err("No driver configured for tpm-rng device\n");
>
> That is a lot of code size for the string that will likely never
> happen. You can use
>
> > +               return 0;
>
> You should report the error.
>
> > +       }
> > +
> > +       if (ret) {
> > +               log_err("Unable to bind rng driver with the tpm-rng device\n");
>
> You might want to use
>
>    return log_msg_ret("bind", ret)
>
> since it doesn't add to code since unless you turn on CONFIG_LOG_ERROR_RETURN

Okay.

-sughosh

>
> > +               return ret;
> > +       }
> > +
> > +       return 0;
> > +}
> > +#endif /* !CONFIG_SPL_BUILD && !CONFIG_TPL_BUILD */
> > +
> >  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
> > +#if !IS_ENABLED(CONFIG_SPL_BUILD) && !IS_ENABLED(CONFIG_TPL_BUILD)
>
> Drop that and do it in the function as above
>
> > +       .post_probe             = tpm_uclass_post_probe,
> >  #endif
> >         .per_device_auto        = sizeof(struct tpm_chip_priv),
> >  };
> > diff --git a/lib/Kconfig b/lib/Kconfig
> > index 3c6fa99b1a..0f05c97afc 100644
> > --- a/lib/Kconfig
> > +++ b/lib/Kconfig
> > @@ -341,6 +341,7 @@ source lib/crypt/Kconfig
> >  config TPM
> >         bool "Trusted Platform Module (TPM) Support"
> >         depends on DM
> > +       select DM_RNG
>
> imply might be better, so boards can disable it.
>
> >         help
> >           This enables support for TPMs which can be used to provide security
> >           features for your board. The TPM can be connected via LPC or I2C
> > --
> > 2.25.1
> >
>
> Regards,
> Simon