Re: [PATCH v1 1/1] tpm: tpm_crb_ffa: Only register driver when ACPI TPM2 uses FF-A

[Jarkko Sakkinen]

 On Thu, Nov 12, 2026 at 11:38:07PM +0000, Siddharth Chintamaneni wrote:
> Prior to commit 677042afb97a ("tpm: tpm_crb_ffa: revert defered_probed
> when tpm_crb_ffa is built-in"), built-in tpm_crb_ffa only registered
> tpm_crb_ffa_driver from tpm_crb_ffa_init() after crb_acpi_probe()
> confirmed start_method == ACPI_TPM2_CRB_WITH_ARM_FFA. After that
> commit, tpm_crb_ffa unconditionally registers on the FF-A bus at
> device_initcall time (and when loaded as a module) without checking
> the platform's ACPI TPM2 table.
> 
> A platform's firmware may expose a TPM CRB over FF-A Secure Partition
> for UEFI boot services while advertising a non-FF-A start method to
> the OS in the ACPI TPM2 table. When the ACPI TPM2 table designates a
> non-FF-A start method, Linux has no consumer for tpm_crb_ffa and
> should not probe the FF-A TPM service.
> 
> On Microsoft Cobalt 200 systems, the ACPI TPM2 table does not use
> ACPI_TPM2_CRB_WITH_ARM_FFA, yet ffa_init() discovers the FF-A TPM
> partition and tpm_crb_ffa_probe() unconditionally sends
> CRB_FFA_GET_INTERFACE_VERSION via FFA_MSG_SEND_DIRECT_REQ2/REQ SMC.
> That request wedges the calling CPU in Secure World (with Non-Secure
> interrupts and GICv3 pseudo-NMIs masked), hanging boot with an RCU CPU
> stall:
> 
>   [    5.507519] ARM FF-A: Driver version 1.2
>   [    5.507519] ARM FF-A: Firmware version 1.2 found
>   [    5.507551] ARM FF-A: Notification setup failed -61, not enabled
>   [    7.150580] Freeing initrd memory: 293640K
>   [   65.515248] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
>   [   65.521346] rcu:     10-...0: (3 GPs behind) idle=dd9c/1/0x4000000000000000 softirq=37/37 fqs=5262
>   [   65.530031] rcu:              hardirqs   softirqs   csw/system
>   [   65.535589] rcu:      number:        0          0            0
>   [   65.541146] rcu:     cputime:        0          0            0   ==> 30028(ms)
>   [   65.548102] rcu:     (detected by 66, t=15010 jiffies, g=-951, q=1384 ncpus=132)
>   [   65.555228] Sending NMI from CPU 66 to CPUs 10:
>   [   75.560686] After 10 seconds, these CPUS still haven't responded to the NMI: 10
> 
> Check the ACPI TPM2 table in tpm_crb_ffa_driver_init() and return
> -ENODEV before calling ffa_register() unless the table is present and
> specifies ACPI_TPM2_CRB_WITH_ARM_FFA, matching the check_acpi_tpm2()
> pattern in tpm_tis.c. This ensures Linux only issues FF-A TPM requests
>
> when ACPI advertises the FF-A start method (for both built-in and
> modular builds), while preserving normal FF-A bus probing on platforms
> that use CRB over FF-A.
> 
> Fixes: 677042afb97a ("tpm: tpm_crb_ffa: revert defered_probed when tpm_crb_ffa is built-in")
> Fixes: eb93f0734ef1 ("tpm_crb: ffa_tpm: Implement driver compliant to CRB over FF-A")

Pick the older.

I attached a prepending patch that caches the start method, which can be
later used in tpm_tis and tpm_crb.

So that totals four patches:

1. My patch.
2. Your fix using the cached value.
3. tpm_tis update to use the cached value.
4. tpm_crb update to use the cached value.

Fast-forward when these are in the mainline, I can send my change with
Stable-dep-of tag to stable@xxxxxxxxxxxxxxx.

Br, Jarkko