linux-kernel - [PATCH v2] serial: imx: adapt rx buffer and dma periods

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Date:   Thu, 19 Sep 2019 12:26:28 +0200
From:   Philipp Puschmann <philipp.puschmann@...ix.com>
To:     linux-kernel@...r.kernel.org
Cc:     gregkh@...uxfoundation.org, yibin.gong@....com,
        fugang.duan@....com, l.stach@...gutronix.de, jslaby@...e.com,
        shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
        festevam@...il.com, linux-imx@....com,
        linux-serial@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Philipp Puschmann <philipp.puschmann@...ix.com>
Subject: [PATCH v2] serial: imx: adapt rx buffer and dma periods

Using only 4 DMA periods for UART RX is very few if we have a high
frequency of small transfers - like in our case using Bluetooth with
many small packets via UART - causing many dma transfers but in each
only filling a fraction of a single buffer. Such a case may lead to
the situation that DMA RX transfer is triggered but no free buffer is
available. While we have addressed the dma handling already with
"dmaengine: imx-sdma: fix dma freezes" we still want to avoid
UART RX FIFO overrun. So we decrease the size of the buffers and
increase their number and the total buffer size.

Signed-off-by: Philipp Puschmann <philipp.puschmann@...ix.com>
Reviewed-by: Lucas Stach <l.stach@...gutronix.de>
---

Changelog v2:
 - split this patch from series "Fix UART DMA freezes for iMX6"
 - add Reviewed-by tag

 drivers/tty/serial/imx.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 87c58f9f6390..51dc19833eab 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1034,8 +1034,6 @@ static void imx_uart_timeout(struct timer_list *t)
 	}
 }
 
-#define RX_BUF_SIZE	(PAGE_SIZE)
-
 /*
  * There are two kinds of RX DMA interrupts(such as in the MX6Q):
  *   [1] the RX DMA buffer is full.
@@ -1118,7 +1116,8 @@ static void imx_uart_dma_rx_callback(void *data)
 }
 
 /* RX DMA buffer periods */
-#define RX_DMA_PERIODS 4
+#define RX_DMA_PERIODS	16
+#define RX_BUF_SIZE	(PAGE_SIZE / 4)
 
 static int imx_uart_start_rx_dma(struct imx_port *sport)
 {
-- 
2.23.0