serial: pl011: Avoid assumptions about buffer size when refilling TX DMA

The existing code assumed that PL011_DMA_BUFFER_SIZE == UART_XMIT_SIZE,
which may not always be the case.  This allows for these two being
different sizes and not copying too much data.

Signed-off-by: Andrew Jackson <Andrew.Jackson@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 8654049a70c0..6153a42d68db 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -501,7 +501,11 @@ static int pl011_dma_tx_refill(struct uart_amba_port *uap)
                 memcpy(&dmatx->buf[0], &xmit->buf[xmit->tail], count);
         else {
                 size_t first = UART_XMIT_SIZE - xmit->tail;
-                size_t second = xmit->head;
+                size_t second;
+
+                if (first > count)
+                        first = count;
+                second = count - first;
 
                 memcpy(&dmatx->buf[0], &xmit->buf[xmit->tail], first);
                 if (second)