Hi Sughosh,
On Fri, 4 Mar 2022 at 06:44, Sughosh Ganu sughosh.ganu@linaro.org wrote:
hi Simon,
On Fri, 4 Mar 2022 at 08:07, Simon Glass sjg@chromium.org wrote:
Hi Sughosh,
On Thu, 3 Mar 2022 at 05:11, Sughosh Ganu sughosh.ganu@linaro.org wrote:
hi Simon,
On Thu, 3 Mar 2022 at 09:18, Simon Glass sjg@chromium.org wrote:
Hi Sughosh,
On Tue, 1 Mar 2022 at 21:53, Sughosh Ganu sughosh.ganu@linaro.org wrote:
hi Simon,
On Tue, 1 Mar 2022 at 20:29, Simon Glass sjg@chromium.org wrote:
Hi Sughosh,
On Mon, 28 Feb 2022 at 05:07, Sughosh Ganu sughosh.ganu@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@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.
What does checking for CONFIG_TPM have to do with SPL and TPL? If that option is enabled, the feature will be active in SPL and TPL too.
Maybe I am not explaining it properly. We need the addition of the RNG child device only in the u-boot proper stage, not in the SPL and TPL stages. The TPM uclass driver can indeed be built for the SPL and TPL stages, while the RNG uclass is needed only for u-boot proper. So, the addition of the RNG child device done in the TPM uclass driver should only happen in u-boot proper, and not in SPL/TPL stages. Which is the reason for the CONFIG_TPM check.
Let me try one more time. If this doesn't work, please chat with a colleague.
The way we do that is with Kconfig options. We don't use ad-hoc methods to enable things in U-Boot proper but not SPL. Boards that have CONFIG_TPM set have it set everywhere, including in SPL. So checking for CONFIG_TPM is going to return true in both U-Boot proper and SPL. If you want different behaviour in SPL, you need CONFIG_SPL_TPM. But even that is indirect, as I have explained. To enable your driver in SPL, you need a CONFIG_SPL_...
Also, you should use devicetree to provide the random number generator, just a device_bind(). Add the node as a subnode of the TPM. Otherwise it cannot work with OF_PLATDATA.
Also I see another problem, on further examination. You cannot start up the TPM in the pre_probe() function. That needs to be done under board control. E.g. for coral it happens in the TPL (or soon VPL) phase so cannot be done again in U-Boot proper.
I tested running the RNG command after the TPM device has already been probed and tpm_startup has been called. Even if I call the tpm_startup again, I do not see any issues. Does the TPM spec prohibit calling the initialisation function multiple times. I believe that the TPM device should be able to handle this scenario right?
I hangs on coral, for example.
So perhaps we need to remember the state of the TPM (using SPL handoff perhaps). Also you probably need to move the startup stuff to the RNG itself.
I can move the call to tpm_startup to the RNG driver's probe function. But I thought it is better that the parent device(TPM) is initialised before calling the probe of the child device.
We use lazy init in U-Boot, so it should be possible to probe the TPM without automatically starting it. Otherwise you are going to break some of the tpm commands.
Perhaps we could add a new function to handle this, which can be called from your rand driver.
int tpm_ensure_started(struct udevice *dev, enum tpm_startup_type mode)
Okay, I can add this, but the question is, does calling the tpm_startup function cause issues? If not, maybe this is not needed?
It does on coral. I don't know whether other TPMs are tolerant of it, but in any case it is not a good idea.
Regards, Simon