linux-kernel - [PATCH v4 1/1] tpm_crb_ffa: handle tpm busy return code

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Message-ID: <20250613233132.4167653-2-prachotan.bathi@arm.com>
Date: Fri, 13 Jun 2025 18:31:32 -0500
From: Prachotan Bathi <prachotan.bathi@....com>
To: Peter Huewe <peterhuewe@....de>,
	Jarkko Sakkinen <jarkko@...nel.org>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Stuart Yoder <stuart.yoder@....com>
Cc: linux-integrity@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Prachotan Bathi <prachotan.bathi@....com>
Subject: [PATCH v4 1/1] tpm_crb_ffa: handle tpm busy return code

For CRB over FF-A interface, if the firmwre TPM or TPM service [1] shares
its Secure Partition (SP) with another service, message requests may
fail with a -EBUSY error. Platforms supporting direct message request v2[1]
 can support secure partitions that support multiple services.

To handle this, replace the single check and call with a retry loop
that attempts the TPM message send operation until it succeeds or a
configurable timeout is reached. The retry mechanism introduces a
module parameter (`busy_timeout`, default: 2000ms) to control how long
to keep retrying on -EBUSY responses. Between retries, the code waits
briefly (50-100 microseconds) to avoid busy-waiting and handling
TPM BUSY conditions more gracefully.

[1] TPM Service Command Response Buffer Interface Over FF-A
https://developer.arm.com/documentation/den0138/latest/

Signed-off-by: Prachotan Bathi <prachotan.bathi@....com>
---
 drivers/char/tpm/tpm_crb_ffa.c | 74 +++++++++++++++++++++++-----------
 1 file changed, 50 insertions(+), 24 deletions(-)

diff --git a/drivers/char/tpm/tpm_crb_ffa.c b/drivers/char/tpm/tpm_crb_ffa.c
index 4ead61f01299..e47e110bac9e 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 +204,47 @@ 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);
+		}
+		if (ret == -EBUSY)
+			pr_err("TPM says busy, trying again, value, ret: %d\n",
+			       ret);
+		else
+			break;
+		usleep_range(50, 100);
+	} while (ktime_before(ktime_get(), stop));
 
 	return ret;
 }
-- 
2.43.0