AMD General Hi Ilias,
> From: Ilias Apalodimas <[email protected]> > Sent: Tuesday, June 9, 2026 4:06 PM > To: Begari, Padmarao <[email protected]> > Cc: [email protected]; Simek, Michal <[email protected]>; git (AMD- > Xilinx) <[email protected]>; Sughosh Ganu <[email protected]>; Heinrich > Schuchardt <[email protected]>; Tom Rini <[email protected]> > Subject: Re: [PATCH] rng: tpm_rng: start TPM before reading random numbers > > Hi Padmarao > > > On Tue, 9 Jun 2026 at 13:10, Padmarao Begari <[email protected]> > wrote: > > > > The tpm-rng driver calls tpm_get_random() without first ensuring the > > TPM device is opened and started. When systemd-boot or fdt_fixup_kaslr > > triggers an RNG read early in boot, the TPM2 device hasn't been > > initialized yet, causing the command to fail: > > Is systemd_boot called via EFI? If so the TPM should be up already. You're right, The EFI TCG2 protocol does start the TPM, but only when tcg2_platform_get_tpm2() returns a probed TPM2 device. That function iterates with for_each_tpm_device(), and the uclass iterator silently skips any device whose probe fails, returning -ENODEV. So, a failed probe means EFI never starts the TPM. The failure (tpm-rng tpm-rng: dm_rng_read failed: -1) does not come from systemd-boot, it comes from U-Boot's own fdt_kaslrseed() call, which runs during bootefi/bootmgr setup before control is handed to the EFI app. > About fdt_fixup_kaslr(), why do you need this? We specifically clear the > kaslr-seed > when booting via EFI and EFI_RNG is installed, since the kernel ignores it. Agree, referencing fdt_fixup_kaslr() in the commit message is a mistake, I'll correct the commit message. Regards Padmarao > > Thanks > /Ilias > > > > tpm-rng tpm-rng: dm_rng_read failed: -1 > > > > Fix this by calling tpm_auto_start() on the parent TPM device before > > tpm_get_random(). This ensures the TPM is initialized before use. > > > > Fixes: e67ffb5aa5ab ("tpm: rng: Add driver model interface for TPM RNG > > device") > > Signed-off-by: Padmarao Begari <[email protected]> > > --- > > drivers/rng/tpm_rng.c | 10 +++++++++- > > 1 file changed, 9 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/rng/tpm_rng.c b/drivers/rng/tpm_rng.c index > > 1a5e9e2e4b4..374e0ac1ff8 100644 > > --- a/drivers/rng/tpm_rng.c > > +++ b/drivers/rng/tpm_rng.c > > @@ -4,12 +4,20 @@ > > */ > > > > #include <dm.h> > > +#include <log.h> > > #include <rng.h> > > #include <tpm_api.h> > > > > static int rng_tpm_random_read(struct udevice *dev, void *data, > > size_t count) { > > - return tpm_get_random(dev_get_parent(dev), data, count); > > + struct udevice *tpm_dev = dev_get_parent(dev); > > + u32 rc; > > + > > + rc = tpm_auto_start(tpm_dev); > > + if (rc) > > + return log_msg_ret("start", -EIO); > > + > > + return tpm_get_random(tpm_dev, data, count); > > } > > > > static const struct dm_rng_ops tpm_rng_ops = { > > -- > > 2.34.1 > >
