[PATCH v2] usb: ucsi: stm32: fix command completion handling

[Fabrice Gasnier]

Sometimes errors are seen, when doing DR swap, like:
[   24.672481] ucsi-stm32g0-i2c 0-0035: UCSI_GET_PDOS failed (-5)
[   24.720188] ucsi-stm32g0-i2c 0-0035: ucsi_handle_connector_change:
 GET_CONNECTOR_STATUS failed (-5)

There may be some race, which lead to read CCI, before the command complete
flag is set, hence returning -EIO. Similar fix has been done also in
ucsi_acpi [1].

In case of a spurious or otherwise delayed notification it is
possible that CCI still reports the previous completion. The
UCSI spec is aware of this and provides two completion bits in
CCI, one for normal commands and one for acks. As acks and commands
alternate the notification handler can determine if the completion
bit is from the current command.

To fix this add the ACK_PENDING bit for ucsi_stm32g0 and only complete
commands if the completion bit matches.

[1] https://lore.kernel.org/lkml/20240121204123.275441-3-lk@c--e.de/

Fixes: 72849d4fcee7 ("usb: typec: ucsi: stm32g0: add support for stm32g0 controller")
Signed-off-by: Fabrice Gasnier <fabrice.gasnier at foss.st.com>
---
Changes in v2: rebase and define ACK_PENDING as commented by Dmitry.
---
 drivers/usb/typec/ucsi/ucsi_stm32g0.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/typec/ucsi/ucsi_stm32g0.c b/drivers/usb/typec/ucsi/ucsi_stm32g0.c
index ac48b7763114..ac69288e8bb0 100644
--- a/drivers/usb/typec/ucsi/ucsi_stm32g0.c
+++ b/drivers/usb/typec/ucsi/ucsi_stm32g0.c
@@ -65,6 +65,7 @@ struct ucsi_stm32g0 {
 	struct device *dev;
 	unsigned long flags;
 #define COMMAND_PENDING	1
+#define ACK_PENDING	2
 	const char *fw_name;
 	struct ucsi *ucsi;
 	bool suspended;
@@ -396,9 +397,13 @@ static int ucsi_stm32g0_sync_write(struct ucsi *ucsi, unsigned int offset, const
 				   size_t len)
 {
 	struct ucsi_stm32g0 *g0 = ucsi_get_drvdata(ucsi);
+	bool ack = UCSI_COMMAND(*(u64 *)val) == UCSI_ACK_CC_CI;
 	int ret;
 
-	set_bit(COMMAND_PENDING, &g0->flags);
+	if (ack)
+		set_bit(ACK_PENDING, &g0->flags);
+	else
+		set_bit(COMMAND_PENDING, &g0->flags);
 
 	ret = ucsi_stm32g0_async_write(ucsi, offset, val, len);
 	if (ret)
@@ -406,9 +411,14 @@ static int ucsi_stm32g0_sync_write(struct ucsi *ucsi, unsigned int offset, const
 
 	if (!wait_for_completion_timeout(&g0->complete, msecs_to_jiffies(5000)))
 		ret = -ETIMEDOUT;
+	else
+		return 0;
 
 out_clear_bit:
-	clear_bit(COMMAND_PENDING, &g0->flags);
+	if (ack)
+		clear_bit(ACK_PENDING, &g0->flags);
+	else
+		clear_bit(COMMAND_PENDING, &g0->flags);
 
 	return ret;
 }
@@ -429,8 +439,9 @@ static irqreturn_t ucsi_stm32g0_irq_handler(int irq, void *data)
 	if (UCSI_CCI_CONNECTOR(cci))
 		ucsi_connector_change(g0->ucsi, UCSI_CCI_CONNECTOR(cci));
 
-	if (test_bit(COMMAND_PENDING, &g0->flags) &&
-	    cci & (UCSI_CCI_ACK_COMPLETE | UCSI_CCI_COMMAND_COMPLETE))
+	if (cci & UCSI_CCI_ACK_COMPLETE && test_and_clear_bit(ACK_PENDING, &g0->flags))
+		complete(&g0->complete);
+	if (cci & UCSI_CCI_COMMAND_COMPLETE && test_and_clear_bit(COMMAND_PENDING, &g0->flags))
 		complete(&g0->complete);
 
 	return IRQ_HANDLED;
-- 
2.25.1