[PATCH v2 0/1] tpm_crb_ffa: handle tpm busy return code

[PATCH v2 0/1] tpm_crb_ffa: handle tpm busy return code

[Prachotan Bathi]

Platforms supporting direct message request v2 can
support SPs that support multiple services.
If the TPM service is sharing the SP with another service,
it could get an error code of BUSY if the other service is
in process.
We need a way for the driver to retry sending the message
to the TPM service until it succeeds or we know that no forward progress
can be made.
This adds a parameterized variable (default 2000ms)
that indicates the maximum time to keep retrying for.

This is building on top of commit a85b55ee64a5da58c6e2c69e2648023189210eae.
A tpm service can be accessed by the driver using direct message request v2 
interface according to chapter 3.3, TPM Service Command Response Buffer 
Interface Over FF-A specificationi v1.0 EAC.

Prachotan Bathi (1):
  tpm_crb_ffa: handle tpm busy return code

 drivers/char/tpm/tpm_crb_ffa.c | 78 +++++++++++++++++++++++-----------
 1 file changed, 54 insertions(+), 24 deletions(-)

-- 
2.43.0

[PATCH v2 1/1] tpm_crb_ffa: handle tpm busy return code

[Prachotan Bathi]

Platforms supporting direct message request v2 can
support SPs that support multiple services.
If the TPM service is sharing the SP with another service,
it could get an error code of BUSY if the other service is
in process.
This adds a parameterized variable (default 2000ms)
 that indicates the maximum time to keep retrying for.
When the TPM service returns a BUSY error code, we sleep
 50-100us before retrying again, until we are over the
busy timeout.

Signed-off-by: Prachotan Bathi <prachotan.bathi@arm.com>
---
 drivers/char/tpm/tpm_crb_ffa.c | 78 +++++++++++++++++++++++-----------
 1 file changed, 54 insertions(+), 24 deletions(-)

diff --git a/drivers/char/tpm/tpm_crb_ffa.c b/drivers/char/tpm/tpm_crb_ffa.c
index 4ead61f01299..122984e15971 100644
--- a/drivers/char/tpm/tpm_crb_ffa.c
+++ b/drivers/char/tpm/tpm_crb_ffa.c
@@ -10,6 +10,8 @@
 #define pr_fmt(fmt) "CRB_FFA: " fmt
 
 #include <linux/arm_ffa.h>
+#include <linux/delay.h>
+#include <linux/moduleparam.h>
 #include "tpm_crb_ffa.h"
 
 /* TPM service function status codes */
@@ -178,6 +180,17 @@ int tpm_crb_ffa_init(void)
 }
 EXPORT_SYMBOL_GPL(tpm_crb_ffa_init);
 
+static unsigned int busy_timeout = 2000;
+/**
+ * busy_timeout - Maximum time to retry before giving up on busy
+ *
+ * This parameter defines the maximum time in milliseconds to retry
+ * sending a message to the TPM service before giving up.
+ */
+module_param(busy_timeout, uint, 0644);
+MODULE_PARM_DESC(busy_timeout,
+		 "Maximum time to retry before giving up on busy");
+
 static int __tpm_crb_ffa_send_recieve(unsigned long func_id,
 				      unsigned long a0,
 				      unsigned long a1,
@@ -191,34 +204,51 @@ static int __tpm_crb_ffa_send_recieve(unsigned long func_id,
 
 	msg_ops = tpm_crb_ffa->ffa_dev->ops->msg_ops;
 
-	if (ffa_partition_supports_direct_req2_recv(tpm_crb_ffa->ffa_dev)) {
-		memset(&tpm_crb_ffa->direct_msg_data2, 0x00,
-		       sizeof(struct ffa_send_direct_data2));
+	ktime_t start;
+	ktime_t stop;
+
+	start = ktime_get();
+	stop = ktime_add(start, ms_to_ktime(busy_timeout));
+
+	do {
+		if (ffa_partition_supports_direct_req2_recv(tpm_crb_ffa->ffa_dev)) {
+			memset(&tpm_crb_ffa->direct_msg_data2, 0x00,
+			       sizeof(struct ffa_send_direct_data2));
 
-		tpm_crb_ffa->direct_msg_data2.data[0] = func_id;
-		tpm_crb_ffa->direct_msg_data2.data[1] = a0;
-		tpm_crb_ffa->direct_msg_data2.data[2] = a1;
-		tpm_crb_ffa->direct_msg_data2.data[3] = a2;
+			tpm_crb_ffa->direct_msg_data2.data[0] = func_id;
+			tpm_crb_ffa->direct_msg_data2.data[1] = a0;
+			tpm_crb_ffa->direct_msg_data2.data[2] = a1;
+			tpm_crb_ffa->direct_msg_data2.data[3] = a2;
 
-		ret = msg_ops->sync_send_receive2(tpm_crb_ffa->ffa_dev,
+			ret = msg_ops->sync_send_receive2(tpm_crb_ffa->ffa_dev,
 				&tpm_crb_ffa->direct_msg_data2);
-		if (!ret)
-			ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data2.data[0]);
-	} else {
-		memset(&tpm_crb_ffa->direct_msg_data, 0x00,
-		       sizeof(struct ffa_send_direct_data));
-
-		tpm_crb_ffa->direct_msg_data.data1 = func_id;
-		tpm_crb_ffa->direct_msg_data.data2 = a0;
-		tpm_crb_ffa->direct_msg_data.data3 = a1;
-		tpm_crb_ffa->direct_msg_data.data4 = a2;
-
-		ret = msg_ops->sync_send_receive(tpm_crb_ffa->ffa_dev,
-				&tpm_crb_ffa->direct_msg_data);
-		if (!ret)
-			ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data.data1);
-	}
+			if (!ret)
+				ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data2.data[0]);
+		} else {
+			memset(&tpm_crb_ffa->direct_msg_data, 0x00,
+			       sizeof(struct ffa_send_direct_data));
 
+			tpm_crb_ffa->direct_msg_data.data1 = func_id;
+			tpm_crb_ffa->direct_msg_data.data2 = a0;
+			tpm_crb_ffa->direct_msg_data.data3 = a1;
+			tpm_crb_ffa->direct_msg_data.data4 = a2;
+
+			ret = msg_ops->sync_send_receive(tpm_crb_ffa->ffa_dev,
+				&tpm_crb_ffa->direct_msg_data);
+			if (!ret)
+				ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data.data1);
+		}
+		// Check if the TPM service returned busy
+		if (ret == -EBUSY)
+			pr_err("TPM says busy, trying again, value, ret: %d\n",
+			       ret);
+		else
+			// If TPM did not return busy, we are done, exit the loop
+			break;
+		// Sleep for a short time before retrying to avoid busy looping
+		usleep_range(50, 100);
+	} while (ktime_before(ktime_get(), stop));
+	// If we are here, we either got a valid response or we are over the busy timeout
 
 	return ret;
 }
-- 
2.43.0

Re: [PATCH v2 1/1] tpm_crb_ffa: handle tpm busy return code

[Jarkko Sakkinen]

On Tue, Jun 10, 2025 at 04:35:05PM -0500, Prachotan Bathi wrote:
> Platforms supporting direct message request v2 can
> support SPs that support multiple services.
> If the TPM service is sharing the SP with another service,
> it could get an error code of BUSY if the other service is
> in process.
> This adds a parameterized variable (default 2000ms)
>  that indicates the maximum time to keep retrying for.
> When the TPM service returns a BUSY error code, we sleep
>  50-100us before retrying again, until we are over the
> busy timeout.
> 
> Signed-off-by: Prachotan Bathi <prachotan.bathi@arm.com>
> ---
>  drivers/char/tpm/tpm_crb_ffa.c | 78 +++++++++++++++++++++++-----------
>  1 file changed, 54 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_crb_ffa.c b/drivers/char/tpm/tpm_crb_ffa.c
> index 4ead61f01299..122984e15971 100644
> --- a/drivers/char/tpm/tpm_crb_ffa.c
> +++ b/drivers/char/tpm/tpm_crb_ffa.c
> @@ -10,6 +10,8 @@
>  #define pr_fmt(fmt) "CRB_FFA: " fmt
>  
>  #include <linux/arm_ffa.h>
> +#include <linux/delay.h>
> +#include <linux/moduleparam.h>
>  #include "tpm_crb_ffa.h"
>  
>  /* TPM service function status codes */
> @@ -178,6 +180,17 @@ int tpm_crb_ffa_init(void)
>  }
>  EXPORT_SYMBOL_GPL(tpm_crb_ffa_init);
>  
> +static unsigned int busy_timeout = 2000;
> +/**
> + * busy_timeout - Maximum time to retry before giving up on busy
> + *
> + * This parameter defines the maximum time in milliseconds to retry
> + * sending a message to the TPM service before giving up.
> + */
> +module_param(busy_timeout, uint, 0644);
> +MODULE_PARM_DESC(busy_timeout,
> +		 "Maximum time to retry before giving up on busy");
> +
>  static int __tpm_crb_ffa_send_recieve(unsigned long func_id,
>  				      unsigned long a0,
>  				      unsigned long a1,
> @@ -191,34 +204,51 @@ static int __tpm_crb_ffa_send_recieve(unsigned long func_id,
>  
>  	msg_ops = tpm_crb_ffa->ffa_dev->ops->msg_ops;
>  
> -	if (ffa_partition_supports_direct_req2_recv(tpm_crb_ffa->ffa_dev)) {
> -		memset(&tpm_crb_ffa->direct_msg_data2, 0x00,
> -		       sizeof(struct ffa_send_direct_data2));
> +	ktime_t start;
> +	ktime_t stop;
> +
> +	start = ktime_get();
> +	stop = ktime_add(start, ms_to_ktime(busy_timeout));
> +
> +	do {
> +		if (ffa_partition_supports_direct_req2_recv(tpm_crb_ffa->ffa_dev)) {
> +			memset(&tpm_crb_ffa->direct_msg_data2, 0x00,
> +			       sizeof(struct ffa_send_direct_data2));
>  
> -		tpm_crb_ffa->direct_msg_data2.data[0] = func_id;
> -		tpm_crb_ffa->direct_msg_data2.data[1] = a0;
> -		tpm_crb_ffa->direct_msg_data2.data[2] = a1;
> -		tpm_crb_ffa->direct_msg_data2.data[3] = a2;
> +			tpm_crb_ffa->direct_msg_data2.data[0] = func_id;
> +			tpm_crb_ffa->direct_msg_data2.data[1] = a0;
> +			tpm_crb_ffa->direct_msg_data2.data[2] = a1;
> +			tpm_crb_ffa->direct_msg_data2.data[3] = a2;
>  
> -		ret = msg_ops->sync_send_receive2(tpm_crb_ffa->ffa_dev,
> +			ret = msg_ops->sync_send_receive2(tpm_crb_ffa->ffa_dev,
>  				&tpm_crb_ffa->direct_msg_data2);
> -		if (!ret)
> -			ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data2.data[0]);
> -	} else {
> -		memset(&tpm_crb_ffa->direct_msg_data, 0x00,
> -		       sizeof(struct ffa_send_direct_data));
> -
> -		tpm_crb_ffa->direct_msg_data.data1 = func_id;
> -		tpm_crb_ffa->direct_msg_data.data2 = a0;
> -		tpm_crb_ffa->direct_msg_data.data3 = a1;
> -		tpm_crb_ffa->direct_msg_data.data4 = a2;
> -
> -		ret = msg_ops->sync_send_receive(tpm_crb_ffa->ffa_dev,
> -				&tpm_crb_ffa->direct_msg_data);
> -		if (!ret)
> -			ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data.data1);
> -	}
> +			if (!ret)
> +				ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data2.data[0]);
> +		} else {
> +			memset(&tpm_crb_ffa->direct_msg_data, 0x00,
> +			       sizeof(struct ffa_send_direct_data));
>  
> +			tpm_crb_ffa->direct_msg_data.data1 = func_id;
> +			tpm_crb_ffa->direct_msg_data.data2 = a0;
> +			tpm_crb_ffa->direct_msg_data.data3 = a1;
> +			tpm_crb_ffa->direct_msg_data.data4 = a2;
> +
> +			ret = msg_ops->sync_send_receive(tpm_crb_ffa->ffa_dev,
> +				&tpm_crb_ffa->direct_msg_data);
> +			if (!ret)
> +				ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data.data1);
> +		}
> +		// Check if the TPM service returned busy
> +		if (ret == -EBUSY)
> +			pr_err("TPM says busy, trying again, value, ret: %d\n",
> +			       ret);
> +		else
> +			// If TPM did not return busy, we are done, exit the loop
> +			break;
> +		// Sleep for a short time before retrying to avoid busy looping
> +		usleep_range(50, 100);
> +	} while (ktime_before(ktime_get(), stop));
> +	// If we are here, we either got a valid response or we are over the busy timeout

Please use "/* */". We don't use C++ comment style:

https://www.kernel.org/doc/html/v6.14/process/coding-style.html#commenting

BR, Jarkko