Patch "serial: samsung: fix DMA mode enter condition for small FIFO sizes" has been added to the 4.1-stable tree

Patch "serial: samsung: fix DMA mode enter condition for small FIFO sizes" has been added to the 4.1-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    serial: samsung: fix DMA mode enter condition for small FIFO sizes

to the 4.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     serial-samsung-fix-dma-mode-enter-condition-for-small-fifo-sizes.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 81ccb2a69f76b88295a1da9fc9484df715fe3bfa Mon Sep 17 00:00:00 2001
From: Marek Szyprowski <m.szyprowski@samsung.com>
Date: Fri, 31 Jul 2015 10:58:27 +0200
Subject: serial: samsung: fix DMA mode enter condition for small FIFO sizes

From: Marek Szyprowski <m.szyprowski@samsung.com>

commit 81ccb2a69f76b88295a1da9fc9484df715fe3bfa upstream.

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.

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>

---
 drivers/tty/serial/samsung.c |   13 +++++++++++--
 drivers/tty/serial/samsung.h |    1 +
 2 files changed, 12 insertions(+), 2 deletions(-)

--- a/drivers/tty/serial/samsung.c
+++ b/drivers/tty/serial/samsung.c
@@ -342,7 +342,8 @@ static void s3c24xx_serial_start_next_tx
 		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);
@@ -742,7 +743,8 @@ static irqreturn_t s3c24xx_serial_tx_cha
 
 	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;
 	}
@@ -1838,6 +1840,13 @@ static int s3c24xx_serial_probe(struct p
 	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);
--- a/drivers/tty/serial/samsung.h
+++ b/drivers/tty/serial/samsung.h
@@ -82,6 +82,7 @@ struct s3c24xx_uart_port {
 	unsigned char			tx_claimed;
 	unsigned int			pm_level;
 	unsigned long			baudclk_rate;
+	unsigned int			min_dma_size;
 
 	unsigned int			rx_irq;
 	unsigned int			tx_irq;


Patches currently in stable-queue which might be from m.szyprowski@samsung.com are

queue-4.1/serial-samsung-fix-dma-mode-enter-condition-for-small-fifo-sizes.patch
queue-4.1/clk-s5pv210-add-missing-call-to.patch