[PATCH v1] platform/surface: aggregator: fix recv_buf() return value

[Francesco Dolcini]

From: Francesco Dolcini <francesco.dolcini@xxxxxxxxxxx>

Serdev recv_buf() callback is supposed to return the amount of bytes
consumed, therefore an int in between 0 and count.

Do not return negative number in case of issue, when
ssam_controller_receive_buf() returns ESHUTDOWN just returns 0, e.g. no
bytes consumed, this keep the exact same behavior as it was before.

This fixes a potential WARN in serdev-ttyport.c:ttyport_receive_buf().

Cc: <stable@xxxxxxxxxxxxxxx>
Fixes: c167b9c7e3d6 ("platform/surface: Add Surface Aggregator subsystem")
Signed-off-by: Francesco Dolcini <francesco.dolcini@xxxxxxxxxxx>
---
 drivers/platform/surface/aggregator/core.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/platform/surface/aggregator/core.c b/drivers/platform/surface/aggregator/core.c
index 1a6373dea109..6152be38398c 100644
--- a/drivers/platform/surface/aggregator/core.c
+++ b/drivers/platform/surface/aggregator/core.c
@@ -231,9 +231,12 @@ static int ssam_receive_buf(struct serdev_device *dev, const unsigned char *buf,
 			    size_t n)
 {
 	struct ssam_controller *ctrl;
+	int ret;
 
 	ctrl = serdev_device_get_drvdata(dev);
-	return ssam_controller_receive_buf(ctrl, buf, n);
+	ret = ssam_controller_receive_buf(ctrl, buf, n);
+
+	return ret < 0 ? 0 : ret;
 }
 
 static void ssam_write_wakeup(struct serdev_device *dev)
-- 
2.25.1