[PATCH v2 08/10] tpm: Add the RNG child device

[Sughosh Ganu]

hi Simon,

On Thu, 3 Mar 2022 at 09:18, Simon Glass <sjg at chromium.org> wrote:
>
> Hi Sughosh,
>
> On Tue, 1 Mar 2022 at 21:53, Sughosh Ganu <sughosh.ganu at linaro.org> wrote:
> >
> > hi Simon,
> >
> > On Tue, 1 Mar 2022 at 20:29, Simon Glass <sjg at chromium.org> wrote:
> > >
> > > Hi Sughosh,
> > >
> > > On Mon, 28 Feb 2022 at 05:07, 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 V1: None
> > > >
> > > >  drivers/tpm/tpm-uclass.c | 58 +++++++++++++++++++++++++++++++++++++---
> > > >  1 file changed, 54 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/drivers/tpm/tpm-uclass.c b/drivers/tpm/tpm-uclass.c
> > > > index 8619da89d8..383cc7bc48 100644
> > > > --- a/drivers/tpm/tpm-uclass.c
> > > > +++ b/drivers/tpm/tpm-uclass.c
> > > > @@ -16,6 +16,11 @@
> > > >  #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"
> > > > +
> > > >  bool is_tpm1(struct udevice *dev)
> > > >  {
> > > >         return IS_ENABLED(CONFIG_TPM_V1) && tpm_get_version(dev) == TPM_V1;
> > > > @@ -147,12 +152,57 @@ int tpm_xfer(struct udevice *dev, const uint8_t *sendbuf, size_t send_size,
> > > >         return 0;
> > > >  }
> > > >
> > > > +#if IS_ENABLED(CONFIG_TPM)
> > >
> > > This should be in the Makefile so that we only build this file if TPM
> > > is enabled.
> >
> > The Makefile allows for the tpm uclass driver to be built for SPL and
> > TPL stages as well. The addition of the RNG device is to be done only
> > in the u-boot proper stage, since we enable RNG support only in u-boot
> > proper. Thanks.
>
> Well in that case, create a new SPL_TPM_RAND or similar to control
> enabling it in SPL. It should be explicit.

I think it is easier to just protect the child addition functions
under CONFIG_TPM rather than create SPL_RNG and TPL_RNG symbols. We
don't have any requirement for generating random numbers in the SPL
and TPL stages. I feel that creating new symbols just for the sake of
not putting a check for CONFIG_TPM is a bit of an overkill, especially
since we do not have any requirement for RNG devices in the SPL/TPL
stages.

-sughosh

>
> Regards,
> Simon