RE: [PATCH v4] serial: 8250_omap: clear rx_running on zero-length DMA completes

[Matthias Feser]

On AM33xx RX DMA only triggers when the FIFO reaches the
configured threshold (typically 48 bytes). For smaller bursts
no DMA request is issued and the FIFO is drained by RX timeout.

In this case __dma_rx_do_complete() can legitimately see count == 0.

The current code exits early in this case and does not clear
dma->rx_running, leaving the DMA state inconsistent. This can
prevent RX DMA from restarting and may cause
omap_8250_rx_dma_flush() to fail, marking DMA as broken.

Fix this by clearing dma->rx_running once the DMA transfer has
completed or been terminated, even if no data was transferred.

Signed-off-by: Matthias Feser <mfe@xxxxxxxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Moteen Shah <m-shah@xxxxxx>
---
Changes in v4:
- Add blank line before dma->rx_running as suggested

Changes in v3:
- Move "Changes in v2" below the tear line as suggested

Changes in v2:
- Move dma->rx_running clear before the count check

 drivers/tty/serial/8250/8250_omap.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index c552c6b9a037..3c7775df27ef 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -944,11 +944,12 @@ static void __dma_rx_do_complete(struct uart_8250_port *p)
 				dev_err(p->port.dev, "teardown incomplete\n");
 		}
 	}
+
+	dma->rx_running = 0;
 	if (!count)
 		goto out;
 	ret = tty_insert_flip_string(tty_port, dma->rx_buf, count);
 
-	dma->rx_running = 0;
 	p->port.icount.rx += ret;
 	p->port.icount.buf_overrun += count - ret;
 out:
-- 
2.39.5