[PATCH 17/28] mfd: loongson-se: Reinitialise completions and wait uninterruptibly for commands

[Lee Jones]

loongson_se_send_controller_cmd() and loongson_se_send_engine_cmd() wait
on se->cmd_completion and engine->completion using
wait_for_completion_interruptible() without reinitialising the
completion before issuing a new command.  Because the hardware has no
mechanism to abort an in-flight command once accepted by
loongson_se_poll(), returning early on a signal leaves the controller or
engine actively processing the shared command registers and DMA buffers
in the background, and its subsequent completion interrupt leaves a
stale completion token that causes the next command to return
prematurely.

Clear any stale pending interrupt status and reinitialise the target
completion inside loongson_se_poll() while holding se->dev_lock
immediately before notifying the controller, and wait uninterruptibly
via wait_for_completion() once loongson_se_poll() confirms the command
has been accepted by the hardware.

Fixes: e551fa3159e3 ("mfd: Add support for Loongson Security Engine chip controller")
Closes: https://sashiko.dev/#/bug/linux-4661fb0d-d936-4168-89cd-2f6dec31a7b5
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Lee Jones <lee@xxxxxxxxxx>
---
 drivers/mfd/loongson-se.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/drivers/mfd/loongson-se.c b/drivers/mfd/loongson-se.c
index 485ee4a6ca5e..9b531e62fb85 100644
--- a/drivers/mfd/loongson-se.c
+++ b/drivers/mfd/loongson-se.c
@@ -37,13 +37,17 @@ struct loongson_se_controller_cmd {
 	u32 info[7];
 };
 
-static int loongson_se_poll(struct loongson_se *se, u32 int_bit)
+static int loongson_se_poll(struct loongson_se *se, u32 int_bit,
+			    struct completion *completion)
 {
 	u32 status;
 	int err;
 
 	spin_lock_irq(&se->dev_lock);
 
+	writel(int_bit, se->base + SE_S2LINT_CL);
+	reinit_completion(completion);
+
 	/* Notify the controller that the engine needs to be started */
 	writel(int_bit, se->base + SE_L2SINT_SET);
 
@@ -66,11 +70,13 @@ static int loongson_se_send_controller_cmd(struct loongson_se *se,
 	for (i = 0; i < SE_SEND_CMD_REG_LEN; i++)
 		writel(send_cmd[i], se->base + SE_SEND_CMD_REG + i * 4);
 
-	err = loongson_se_poll(se, SE_INT_CONTROLLER);
+	err = loongson_se_poll(se, SE_INT_CONTROLLER, &se->cmd_completion);
 	if (err)
 		return err;
 
-	return wait_for_completion_interruptible(&se->cmd_completion);
+	wait_for_completion(&se->cmd_completion);
+
+	return 0;
 }
 
 int loongson_se_send_engine_cmd(struct loongson_se_engine *engine)
@@ -80,12 +86,15 @@ int loongson_se_send_engine_cmd(struct loongson_se_engine *engine)
 	 * where to obtain engine commands from. Now all we need to
 	 * do is notify the controller that the engine needs to be started.
 	 */
-	int err = loongson_se_poll(engine->se, BIT(engine->id));
+	int err = loongson_se_poll(engine->se, BIT(engine->id),
+				   &engine->completion);
 
 	if (err)
 		return err;
 
-	return wait_for_completion_interruptible(&engine->completion);
+	wait_for_completion(&engine->completion);
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(loongson_se_send_engine_cmd);
 
-- 
2.56.0.218.g1ec904b173-goog