Re: [RFC PATCH 2/3] firmware: arm_ffa: initialise ff-a after finalising pKVM initialisation

On Tue, May 05, 2026 at 04:06:51PM +0100, Yeoreum Yun wrote:
> Hi Sudeep,
> 
> > On Tue, May 05, 2026 at 10:54:08AM +0100, Yeoreum Yun wrote:
> > > When pKVM is enabled, the FF-A driver must be initialised after pKVM.
> > > Otherwise, pKVM cannot negotiate the FF-A version or obtain the RX/TX
> > > buffer information, leading to failures in FF-A calls.
> > > 
> > > Currently, pKVM initialisation completes at device_initcall_sync,
> > > while ffa_init() runs at the device_initcall level.
> > > 
> > > So far, linker deployes kvm_arm_init() before ffa_init(), and SMCs can
> > > still be trapped even before finalise_pkvm() is invoked.
> > > As a result, this issue has not been observed.
> > > 
> > > However, relying on above stuff is fragile.
> > > Therefore, when pKVM is enabled, the FF-A infrastructure should be
> > > initialised only after pKVM initialisation has been fully finalised.
> > > 
> > > To achieve this, introduce an ffa_root_dev ("arm-ffa") and
> > > a corresponding driver to defer initialisation of the FF-A infrastructure
> > > until pKVM initialisation is complete, and to defer probing of all FF-A devices until then
> > > when pKVM is enabled.
> > > 
> > 
> > I don't like this whole ffa root device design.
> > Two question for now:
> > 1. Can FF-A be a module on systems with pKVM which removes the need for all
> >    this dance done here ?
> 
> But this means we reduce the other feature e.x) IMA with TPM over
> FF-A and pKVM feature. Since IMA must be a built-in, we couldn't avoid
> to build FF-A driver with built-in.
> 
> > 2. If it is a requirement to have this built-in, I prefer to add a probe
> >    and defer it instead of this root ffa device.
> 
> But, How? anyway all of FF-A device & driver couldn't be probed unless
> FF-A initialisation is finished and How can we trigger FF-A initailise
> after pKVM finish its initialisation?
> 
> The problem is ff-a intiailisation happens before pKVM finish its
> initailasation and to do defer probe, it should use dd-model and
> As we discussed in other thread, notifier couldn't be a soluation.
> 
> Could you let me share other way I'm missing?
> 

Will something like below work ? If we add DT bindings, then we can add
of_match_table and drop the platform device creation. Also we can adjust
the parent device the way you have done by a simple change(not done in
this untested/not compiled change).

Regards,
Sudeep

-->8

firmware: arm_ffa: Register core as a platform driver

Move the FF-A core bring-up and teardown paths into platform driver
probe and remove callbacks, and register a synthetic arm-ffa platform
device to bind the driver.

This makes the FF-A core lifetime follow the driver model while keeping
the device creation internal to the FF-A core. The probe path can now
return normal driver-model errors, including probe deferral when pKVM is
enabled but not yet initialized.

Since the transport selection now happens from the platform probe path,
drop the __init annotation from ffa_transport_init().

Signed-off-by: Sudeep Holla <[email protected]>
---
 drivers/firmware/arm_ffa/common.h |  4 +--
 drivers/firmware/arm_ffa/driver.c | 55 +++++++++++++++++++++++++++----
 drivers/firmware/arm_ffa/smccc.c  |  2 +-
 3 files changed, 52 insertions(+), 9 deletions(-)

diff --git a/drivers/firmware/arm_ffa/common.h b/drivers/firmware/arm_ffa/common.h
index 9c6425a81d0d..5cdf4bd222c6 100644
--- a/drivers/firmware/arm_ffa/common.h
+++ b/drivers/firmware/arm_ffa/common.h
@@ -18,9 +18,9 @@ bool ffa_device_is_valid(struct ffa_device *ffa_dev);
 void ffa_device_match_uuid(struct ffa_device *ffa_dev, const uuid_t *uuid);
 
 #ifdef CONFIG_ARM_FFA_SMCCC
-int __init ffa_transport_init(ffa_fn **invoke_ffa_fn);
+int ffa_transport_init(ffa_fn **invoke_ffa_fn);
 #else
-static inline int __init ffa_transport_init(ffa_fn **invoke_ffa_fn)
+static inline int ffa_transport_init(ffa_fn **invoke_ffa_fn)
 {
 	return -EOPNOTSUPP;
 }
diff --git a/drivers/firmware/arm_ffa/driver.c b/drivers/firmware/arm_ffa/driver.c
index eb2782848283..d000727889f4 100644
--- a/drivers/firmware/arm_ffa/driver.c
+++ b/drivers/firmware/arm_ffa/driver.c
@@ -36,6 +36,7 @@
 #include <linux/mm.h>
 #include <linux/mutex.h>
 #include <linux/of_irq.h>
+#include <linux/platform_device.h>
 #include <linux/scatterlist.h>
 #include <linux/slab.h>
 #include <linux/smp.h>
@@ -46,6 +47,7 @@
 
 #define FFA_DRIVER_VERSION	FFA_VERSION_1_2
 #define FFA_MIN_VERSION		FFA_VERSION_1_0
+#define FFA_PLATFORM_NAME	"arm-ffa"
 
 #define SENDER_ID_MASK		GENMASK(31, 16)
 #define RECEIVER_ID_MASK	GENMASK(15, 0)
@@ -114,6 +116,7 @@ struct ffa_drv_info {
 };
 
 static struct ffa_drv_info *drv_info;
+static struct platform_device *ffa_pdev;
 
 /*
  * The driver must be able to support all the versions from the earliest
@@ -2029,12 +2032,15 @@ static void ffa_notifications_setup(void)
 	ffa_notifications_cleanup();
 }
 
-static int __init ffa_init(void)
+static int ffa_probe(struct platform_device *pdev)
 {
 	int ret;
 	u32 buf_sz;
 	size_t rxtx_bufsz = SZ_4K;
 
+	if (is_protected_kvm_enabled() && !is_pkvm_initialized())
+		return -EPROBE_DEFER;
+
 	ret = ffa_transport_init(&invoke_ffa_fn);
 	if (ret)
 		return ret;
@@ -2042,6 +2048,7 @@ static int __init ffa_init(void)
 	drv_info = kzalloc_obj(*drv_info);
 	if (!drv_info)
 		return -ENOMEM;
+	platform_set_drvdata(pdev, drv_info);
 
 	ret = ffa_version_check(&drv_info->version);
 	if (ret)
@@ -2103,19 +2110,55 @@ static int __init ffa_init(void)
 		free_pages_exact(drv_info->tx_buffer, rxtx_bufsz);
 	free_pages_exact(drv_info->rx_buffer, rxtx_bufsz);
 free_drv_info:
+	platform_set_drvdata(pdev, NULL);
 	kfree(drv_info);
+	drv_info = NULL;
 	return ret;
 }
-rootfs_initcall(ffa_init);
 
-static void __exit ffa_exit(void)
+static void ffa_remove(struct platform_device *pdev)
 {
+	struct ffa_drv_info *info = platform_get_drvdata(pdev);
+
 	ffa_notifications_cleanup();
 	ffa_partitions_cleanup();
 	ffa_rxtx_unmap();
-	free_pages_exact(drv_info->tx_buffer, drv_info->rxtx_bufsz);
-	free_pages_exact(drv_info->rx_buffer, drv_info->rxtx_bufsz);
-	kfree(drv_info);
+	free_pages_exact(info->tx_buffer, info->rxtx_bufsz);
+	free_pages_exact(info->rx_buffer, info->rxtx_bufsz);
+	kfree(info);
+	platform_set_drvdata(pdev, NULL);
+	drv_info = NULL;
+}
+
+static struct platform_driver ffa_driver = {
+	.remove = ffa_remove,
+	.driver = {
+		.name = FFA_PLATFORM_NAME,
+	},
+};
+
+static int __init ffa_init(void)
+{
+	int ret;
+
+	ffa_pdev = platform_device_register_simple(FFA_PLATFORM_NAME,
+						   PLATFORM_DEVID_NONE,
+						   NULL, 0);
+	if (IS_ERR(ffa_pdev))
+		return PTR_ERR(ffa_pdev);
+
+	ret = platform_driver_probe(&ffa_driver, ffa_probe);
+	if (ret)
+		platform_device_unregister(ffa_pdev);
+
+	return ret;
+}
+module_init(ffa_init);
+
+static void __exit ffa_exit(void)
+{
+	platform_device_unregister(ffa_pdev);
+	platform_driver_unregister(&ffa_driver);
 }
 module_exit(ffa_exit);
 
diff --git a/drivers/firmware/arm_ffa/smccc.c b/drivers/firmware/arm_ffa/smccc.c
index 4d85bfff0a4e..e6125dd9f58f 100644
--- a/drivers/firmware/arm_ffa/smccc.c
+++ b/drivers/firmware/arm_ffa/smccc.c
@@ -17,7 +17,7 @@ static void __arm_ffa_fn_hvc(ffa_value_t args, ffa_value_t *res)
 	arm_smccc_1_2_hvc(&args, res);
 }
 
-int __init ffa_transport_init(ffa_fn **invoke_ffa_fn)
+int ffa_transport_init(ffa_fn **invoke_ffa_fn)
 {
 	enum arm_smccc_conduit conduit;
 
-- 
2.43.0