serial: samsung: fix DMA mode enter condition for small FIFO sizes
Due to some of serial ports can have FIFO size smaller than cache line
size, and because of need to align DMA buffer address to cache line size,
it's necessary to calculate minimum number of bytes for which we want
to start DMA transaction to be at least cache line size. The simplest
way to meet this requirement is to get maximum of cache line size and
FIFO size.
Cc: <stable@vger.kernel.org> # v3.18+
Reported-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/serial/samsung.c b/drivers/tty/serial/samsung.c
index 8c963d6..faee021 100644
--- a/drivers/tty/serial/samsung.c
+++ b/drivers/tty/serial/samsung.c
@@ -341,7 +341,8 @@
return;
}
- if (!ourport->dma || !ourport->dma->tx_chan || count < port->fifosize)
+ if (!ourport->dma || !ourport->dma->tx_chan ||
+ count < ourport->min_dma_size)
s3c24xx_serial_start_tx_pio(ourport);
else
s3c24xx_serial_start_tx_dma(ourport, count);
@@ -741,7 +742,8 @@
count = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
- if (ourport->dma && ourport->dma->tx_chan && count >= port->fifosize) {
+ if (ourport->dma && ourport->dma->tx_chan &&
+ count >= ourport->min_dma_size) {
s3c24xx_serial_start_tx_dma(ourport, count);
goto out;
}
@@ -1837,6 +1839,13 @@
else if (ourport->info->fifosize)
ourport->port.fifosize = ourport->info->fifosize;
+ /*
+ * DMA transfers must be aligned at least to cache line size,
+ * so find minimal transfer size suitable for DMA mode
+ */
+ ourport->min_dma_size = max_t(int, ourport->port.fifosize,
+ dma_get_cache_alignment());
+
probe_index++;
dbg("%s: initialising port %p...\n", __func__, ourport);