firmware: exynos-acpm: check saved RX before bailing out on empty RX queue

When we're polling for responses and get a response that corresponds to
another request, we save the RX data in order to drain the RX queue.

If the response for the current request is not found in the request's
iteration of the queue, or if the queue is empty, we must check whether
the RX data was saved by a previous request when it drained the RX queue.

We failed to check for already saved responses when the queue was empty,
and requests could time out. Check saved RX before bailing out on empty
RX queue.

Fixes: a88927b534ba ("firmware: add Exynos ACPM protocol driver")
Reported-by: André Draszik <andre.draszik@linaro.org>
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Reviewed-by: André Draszik <andre.draszik@linaro.org>
Tested-by: André Draszik <andre.draszik@linaro.org>
Link: https://lore.kernel.org/r/20250324-acpm-drained-rx-queue-v1-1-577774335151@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

1 files changed, 30 insertions, 14 deletions

diff --git a/drivers/firmware/samsung/exynos-acpm.c b/drivers/firmware/samsung/exynos-acpm.c
index a85b2dbdd9f0..15e991b99f5a 100644
--- a/drivers/firmware/samsung/exynos-acpm.c
+++ b/drivers/firmware/samsung/exynos-acpm.c
@@ -185,6 +185,29 @@ struct acpm_match_data {
 #define handle_to_acpm_info(h) container_of(h, struct acpm_info, handle)
 
 /**
+ * acpm_get_saved_rx() - get the response if it was already saved.
+ * @achan:	ACPM channel info.
+ * @xfer:	reference to the transfer to get response for.
+ * @tx_seqnum:	xfer TX sequence number.
+ */
+static void acpm_get_saved_rx(struct acpm_chan *achan,
+			      const struct acpm_xfer *xfer, u32 tx_seqnum)
+{
+	const struct acpm_rx_data *rx_data = &achan->rx_data[tx_seqnum - 1];
+	u32 rx_seqnum;
+
+	if (!rx_data->response)
+		return;
+
+	rx_seqnum = FIELD_GET(ACPM_PROTOCOL_SEQNUM, rx_data->cmd[0]);
+
+	if (rx_seqnum == tx_seqnum) {
+		memcpy(xfer->rxd, rx_data->cmd, xfer->rxlen);
+		clear_bit(rx_seqnum - 1, achan->bitmap_seqnum);
+	}
+}
+
+/**
  * acpm_get_rx() - get response from RX queue.
  * @achan:	ACPM channel info.
  * @xfer:	reference to the transfer to get response for.
@@ -204,15 +227,16 @@ static int acpm_get_rx(struct acpm_chan *achan, const struct acpm_xfer *xfer)
 	rx_front = readl(achan->rx.front);
 	i = readl(achan->rx.rear);
 
-	/* Bail out if RX is empty. */
-	if (i == rx_front)
+	tx_seqnum = FIELD_GET(ACPM_PROTOCOL_SEQNUM, xfer->txd[0]);
+
+	if (i == rx_front) {
+		acpm_get_saved_rx(achan, xfer, tx_seqnum);
 		return 0;
+	}
 
 	base = achan->rx.base;
 	mlen = achan->mlen;
 
-	tx_seqnum = FIELD_GET(ACPM_PROTOCOL_SEQNUM, xfer->txd[0]);
-
 	/* Drain RX queue. */
 	do {
 		/* Read RX seqnum. */
@@ -259,16 +283,8 @@ static int acpm_get_rx(struct acpm_chan *achan, const struct acpm_xfer *xfer)
 	 * If the response was not in this iteration of the queue, check if the
 	 * RX data was previously saved.
 	 */
-	rx_data = &achan->rx_data[tx_seqnum - 1];
-	if (!rx_set && rx_data->response) {
-		rx_seqnum = FIELD_GET(ACPM_PROTOCOL_SEQNUM,
-				      rx_data->cmd[0]);
-
-		if (rx_seqnum == tx_seqnum) {
-			memcpy(xfer->rxd, rx_data->cmd, xfer->rxlen);
-			clear_bit(rx_seqnum - 1, achan->bitmap_seqnum);
-		}
-	}
+	if (!rx_set)
+		acpm_get_saved_rx(achan, xfer, tx_seqnum);
 
 	return 0;
 }