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

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

[Siddharth Chintamaneni]

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")
Cc: stable@vger.kernel.org
Signed-off-by: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
---
 drivers/char/tpm/tpm_crb_ffa.c | 37 +++++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/drivers/char/tpm/tpm_crb_ffa.c b/drivers/char/tpm/tpm_crb_ffa.c
index 025c4d4b17ca..8219a8d01344 100644
--- a/drivers/char/tpm/tpm_crb_ffa.c
+++ b/drivers/char/tpm/tpm_crb_ffa.c
@@ -9,6 +9,7 @@
 
 #define pr_fmt(fmt) "CRB_FFA: " fmt
 
+#include <linux/acpi.h>
 #include <linux/arm_ffa.h>
 #include <linux/delay.h>
 #include <linux/moduleparam.h>
@@ -395,7 +396,41 @@ static struct ffa_driver tpm_crb_ffa_driver = {
 	.id_table = tpm_crb_ffa_device_id,
 };
 
-module_ffa_driver(tpm_crb_ffa_driver);
+static bool __init tpm_crb_ffa_has_acpi_tpm2(void)
+{
+	struct acpi_table_tpm2 *buf;
+	acpi_status status;
+	bool match;
+
+	if (acpi_disabled)
+		return false;
+
+	status = acpi_get_table(ACPI_SIG_TPM2, 1,
+				(struct acpi_table_header **)&buf);
+	if (ACPI_FAILURE(status))
+		return false;
+
+	match = buf->header.length >= sizeof(*buf) &&
+		buf->start_method == ACPI_TPM2_CRB_WITH_ARM_FFA;
+	acpi_put_table((struct acpi_table_header *)buf);
+
+	return match;
+}
+
+static int __init tpm_crb_ffa_driver_init(void)
+{
+	if (!tpm_crb_ffa_has_acpi_tpm2())
+		return -ENODEV;
+
+	return ffa_register(&tpm_crb_ffa_driver);
+}
+module_init(tpm_crb_ffa_driver_init);
+
+static void __exit tpm_crb_ffa_driver_exit(void)
+{
+	ffa_unregister(&tpm_crb_ffa_driver);
+}
+module_exit(tpm_crb_ffa_driver_exit);
 
 MODULE_AUTHOR("Arm");
 MODULE_DESCRIPTION("TPM CRB FFA driver");
-- 
2.45.4

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

[Jarkko Sakkinen]

[-- Attachment #1: Type: text/plain, Size: 3193 bytes --]

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@vger.kernel.org.

Br, Jarkko

[-- Attachment #2: 0001-tpm-Cache-TPM2-start-method.patch --]
[-- Type: text/x-diff, Size: 3151 bytes --]

From fc841edc9b4036bed36126dbdc7fdd41cee185c8 Mon Sep 17 00:00:00 2001
From: Jarkko Sakkinen <jarkko@kernel.org>
Date: Fri, 13 Nov 2026 20:18:42 +0200
Subject: [PATCH] tpm: Cache TPM2 start method

Both tpm_tis and tpm_crb have duplicate code for retrieving the start
method from TPM2 ACPI table. Eagerly cache the start method already at chip
creation. The cached chip->start_method can then be used by the leaf
drivers; or ignored depending on the requirements.

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
 drivers/char/tpm/tpm-chip.c | 36 +++++++++++++++++++++++++++++-------
 include/linux/tpm.h         |  1 +
 2 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index 0be5dbfaa72e..540dd366effc 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -256,18 +256,24 @@ int tpm_class_shutdown(struct device *dev)
 }
 
 /**
- * tpm_chip_alloc() - allocate a new struct tpm_chip instance
- * @pdev: device to which the chip is associated
- *        At this point pdev mst be initialized, but does not have to
- *        be registered
- * @ops: struct tpm_class_ops instance
+ * tpm_chip_alloc() - Allocate a new struct tpm_chip instance
+ * @pdev:	device to which the chip is associated At this point pdev mst be
+ *		initialized, but does not have to be registered
+ * @ops:	struct tpm_class_ops for the chip.
+ *
+ * Allocates a new struct tpm_chip instance, and assigns a free device number
+ * for it. Must be paired with put_device(&chip->dev).
  *
- * Allocates a new struct tpm_chip instance and assigns a free
- * device number for it. Must be paired with put_device(&chip->dev).
+ * When ACPI is enabled, additionally tries to eagerly cache the start method
+ * from TPM2 ACPI table for the devices that need know it.
  */
 struct tpm_chip *tpm_chip_alloc(struct device *pdev,
 				const struct tpm_class_ops *ops)
 {
+#ifdef CONFIG_ACPI
+	struct acpi_table_tpm2 *tbl;
+	acpi_status status;
+#endif
 	struct tpm_chip *chip;
 	int rc;
 
@@ -275,6 +281,22 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev,
 	if (chip == NULL)
 		return ERR_PTR(-ENOMEM);
 
+#ifdef CONFIG_ACPI
+	chip->start_method = ACPI_TPM2_NOT_ALLOWED;
+	if (!acpi_disabled) {
+		status = acpi_get_table(ACPI_SIG_TPM2, 1, (struct acpi_table_header **)&tbl);
+		if (!ACPI_FAILURE(status) || tbl->header.length >= sizeof(*tbl)) {
+			chip->start_method = tbl->start_method;
+			dev_info(pdev, "TPM2 ACPI table is available");
+		} else {
+			dev_info(pdev, "TPM2 ACPI table is not available");
+		}
+
+		if (!ACPI_FAILURE(status))
+			acpi_put_table((struct acpi_table_header *)tbl);
+	}
+#endif
+
 	mutex_init(&chip->tpm_mutex);
 	init_rwsem(&chip->ops_sem);
 
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 0db277af45c3..f6cc91615469 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -149,6 +149,7 @@ struct tpm_chip {
 	struct tpm_bank_info allocated_banks[TPM2_MAX_PCR_BANKS];
 #ifdef CONFIG_ACPI
 	acpi_handle acpi_dev_handle;
+	u32 start_method;
 	char ppi_version[TPM_PPI_VERSION_LEN + 1];
 #endif /* CONFIG_ACPI */
 
-- 
2.47.3

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

[Siddharth Chintamaneni]

On Fri, 13 Nov 2026 at 10:31, Jarkko Sakkinen <jarkko@kernel.org> wrote:
>
> 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.
>

Sounds good! I can put together that 4 patch v2 series.

Two quick notes before I spin v2

- Module loading with CONFIG_TCG_CRB=m and CONFIG_TCG_ARM_CRB_FFA=m:
  As Sashiko flagged on v1 [1], because tpm_crb.ko directly references
  tpm_crb_ffa_init() and tpm_crb_ffa_start(), returning -ENODEV from
  tpm_crb_ffa's module_init would prevent modprobe from loading
  tpm_crb.ko on non-FF-A systems. In v2, I will move the start_method
  check into tpm_crb_ffa_probe() (matching check_acpi_tpm2() in tpm_tis)
  so both modules load cleanly while still skipping the FF-A probe on
  non-FF-A platforms

- regarding the location of caching approach -
  tpm_crb_ffa never allocates a struct tpm_chip, and both tpm_tis
  (check_acpi_tpm2()) and tpm_crb (crb_acpi_probe()) check start_method
  before calling tpmm_chip_alloc().  Would it work for you if patch 1
  caches start_method once in tpm_init() (subsys_initcall in
  tpm-interface.c) and exports a small helper (e.g.
  tpm_acpi_start_method()) so tpm_crb_ffa_probe(), tpm_tis, and tpm_crb
  can all query it before chip allocation? (Also noticed a small '||' ->
  '&&' typo on the header.length check in the attached patch.)


[1] https://sashiko.dev/#/patchset/20261112233807.70664-1-sidchintamaneni%40gmail.com

> Fast-forward when these are in the mainline, I can send my change with
> Stable-dep-of tag to stable@vger.kernel.org.
>
> Br, Jarkko

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

[Jarkko Sakkinen]

On Fri, Nov 13, 2026 at 11:31:31AM -0800, Siddharth Chintamaneni wrote:
> On Fri, 13 Nov 2026 at 10:31, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> >
> > 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.
> >
> 
> Sounds good! I can put together that 4 patch v2 series.
> 
> Two quick notes before I spin v2
> 
> - Module loading with CONFIG_TCG_CRB=m and CONFIG_TCG_ARM_CRB_FFA=m:
>   As Sashiko flagged on v1 [1], because tpm_crb.ko directly references
>   tpm_crb_ffa_init() and tpm_crb_ffa_start(), returning -ENODEV from
>   tpm_crb_ffa's module_init would prevent modprobe from loading
>   tpm_crb.ko on non-FF-A systems. In v2, I will move the start_method
>   check into tpm_crb_ffa_probe() (matching check_acpi_tpm2() in tpm_tis)
>   so both modules load cleanly while still skipping the FF-A probe on
>   non-FF-A platforms
> 
> - regarding the location of caching approach -
>   tpm_crb_ffa never allocates a struct tpm_chip, and both tpm_tis
>   (check_acpi_tpm2()) and tpm_crb (crb_acpi_probe()) check start_method
>   before calling tpmm_chip_alloc().  Would it work for you if patch 1
>   caches start_method once in tpm_init() (subsys_initcall in
>   tpm-interface.c) and exports a small helper (e.g.
>   tpm_acpi_start_method()) so tpm_crb_ffa_probe(), tpm_tis, and tpm_crb
>   can all query it before chip allocation? (Also noticed a small '||' ->
>   '&&' typo on the header.length check in the attached patch.)

Move it to tpm_init() and store the result to a global variable, let's
say tpm2_acpi_start_method. There's only one of these so it's all fine.

You can then mark the resulting commit as:

Signed-off-by: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
Co-developed-by: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

I just put those tag because it is easy to mix up with Co-by tag,
when using it.

Br, Jarkko