[PATCH] crypto: eip93 - bound the wait for PE completion

[Rosen Penev <rosenp@gmail.com>]

The tasklet drains result descriptors by polling the descriptor's ready
bits in an unbounded loop. If the DMA engine stalls or reports an error
state instead of PE_READY, the loop busy-waits in softirq context and
locks up the CPU (soft lockup).

Replace the open-coded loop with read_poll_timeout_atomic(), giving the
hardware a 1 ms window to write the result before the tasklet gives up
and re-enables the RDR interrupt.

Fixes: 9739f5f93b78 ("crypto: eip93 - Add Inside Secure SafeXcel EIP-93 crypto engine support")
Assisted-by: LLM
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 .../crypto/inside-secure/eip93/eip93-main.c   | 31 ++++++++++++++-----
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/drivers/crypto/inside-secure/eip93/eip93-main.c b/drivers/crypto/inside-secure/eip93/eip93-main.c
index e62785952b0d..11e20ce33dce 100644
--- a/drivers/crypto/inside-secure/eip93/eip93-main.c
+++ b/drivers/crypto/inside-secure/eip93/eip93-main.c
@@ -11,6 +11,7 @@
 #include <linux/delay.h>
 #include <linux/dma-mapping.h>
 #include <linux/interrupt.h>
+#include <linux/iopoll.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
@@ -183,6 +184,22 @@ static int eip93_register_algs(struct eip93_device *eip93, u32 supported_algo_fl
 	return ret;
 }
 
+#define EIP93_PE_READY_POLL_TIMEOUT_US	1000
+
+static inline u32 eip93_ctrl_status(const struct eip93_descriptor *rdesc)
+{
+	return READ_ONCE(rdesc->pe_ctrl_stat_word);
+}
+
+static inline bool eip93_desc_is_ready(const struct eip93_descriptor *rdesc,
+				       u32 pe_ctrl_stat)
+{
+	return FIELD_GET(EIP93_PE_CTRL_PE_READY_DES_TRING_OWN,
+			 pe_ctrl_stat) == EIP93_PE_CTRL_PE_READY &&
+	       FIELD_GET(EIP93_PE_LENGTH_HOST_PE_READY,
+			 READ_ONCE(rdesc->pe_length_word)) == EIP93_PE_LENGTH_PE_READY;
+}
+
 static void eip93_handle_result_descriptor(struct eip93_device *eip93)
 {
 	struct crypto_async_request *async;
@@ -191,7 +208,6 @@ static void eip93_handle_result_descriptor(struct eip93_device *eip93)
 	bool last_entry;
 	int handled, left, err;
 	u32 pe_ctrl_stat;
-	u32 pe_length;
 
 get_more:
 	handled = 0;
@@ -216,13 +232,12 @@ static void eip93_handle_result_descriptor(struct eip93_device *eip93)
 			break;
 		}
 		/* make sure DMA is finished writing */
-		do {
-			pe_ctrl_stat = READ_ONCE(rdesc->pe_ctrl_stat_word);
-			pe_length = READ_ONCE(rdesc->pe_length_word);
-		} while (FIELD_GET(EIP93_PE_CTRL_PE_READY_DES_TRING_OWN, pe_ctrl_stat) !=
-			 EIP93_PE_CTRL_PE_READY ||
-			 FIELD_GET(EIP93_PE_LENGTH_HOST_PE_READY, pe_length) !=
-			 EIP93_PE_LENGTH_PE_READY);
+		err = read_poll_timeout_atomic(eip93_ctrl_status, pe_ctrl_stat,
+					       eip93_desc_is_ready(rdesc, pe_ctrl_stat),
+					       1, EIP93_PE_READY_POLL_TIMEOUT_US,
+					       false, rdesc);
+		if (err)
+			return;
 
 		err = rdesc->pe_ctrl_stat_word & (EIP93_PE_CTRL_PE_EXT_ERR_CODE |
 						  EIP93_PE_CTRL_PE_EXT_ERR |
-- 
2.55.0