-----Original Message-----
From: Uwe Kleine-König <redacted>
Sent: 2018年9月20日 15:55
To: Robin Gong <redacted>
Cc: jslaby@suse.com; Andy Duan <redacted>;
linux-serial@vger.kernel.org; linux-kernel@vger.kernel.org; dl-linux-imx
[off-list ref]; kernel@pengutronix.de
Subject: Re: [PATCH v1] tty: serial: imx: enable IDDMAEN for the last tail data

Hello,

On Thu, Sep 20, 2018 at 11:26:00PM +0800, Robin Gong wrote:

quoted

enable IDDMAEN in UCR4 to let sdma script has the chance to detect the
idle status and transfer the last tail data with the interrupt
notifying uart driver.Otherwise, the last dma done interrupt of the
tail data in rxfifo whose size is less than watermark may never be
received by uart driver.

Is this a theoretic issue? Or does it fix a real problem?

If the former I'd say UCR1_ATDMAEN being set should prevent this stall.

It's a real fix, you will see 'timeout We read 0 byte' with the attached stress test
running on i.mx7d or i.mx6 if no this patch applied. 
' while [ 1 ]; do /unit_tests/UART/mxc_uart_stress_test.out /dev/ttymxc5 2000000 D L 100 100 L; done &'
Please make sure dma enabled on ttymxcX for your test, and sdma firmware setup in your rootfs 
/lib/firmware/imx/sdma/sdma-imx6q.bin or /lib/firmware/imx/sdma/sdma-imx7d.bin.
You can get sdma firmware from below:
https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/tree/imx/sdma

Also I'd say the SDMA scripts I know don't properly handle the IDDMA request.

Best regards
Uwe

quoted

Signed-off-by: Robin Gong <redacted>
---
 drivers/tty/serial/imx.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index

239c0fa..bbb1693 100644

--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c

@@ -1278,7 +1278,7 @@ static int imx_uart_dma_init(struct imx_port

*sport)

 static void imx_uart_enable_dma(struct imx_port *sport)  {
-	u32 ucr1;
+	u32 ucr1, ucr4;

 	imx_uart_setup_ufcr(sport, TXTL_DMA, RXTL_DMA);

@@ -1287,18 +1287,26 @@ static void imx_uart_enable_dma(struct

imx_port *sport)

quoted

 	ucr1 |= UCR1_RXDMAEN | UCR1_TXDMAEN | UCR1_ATDMAEN;
 	imx_uart_writel(sport, ucr1, UCR1);

+	ucr4 = imx_uart_readl(sport, UCR4);
+	ucr4 |= UCR4_IDDMAEN;
+	imx_uart_writel(sport, ucr4, UCR4);
+
 	sport->dma_is_enabled = 1;
 }

 static void imx_uart_disable_dma(struct imx_port *sport)  {
-	u32 ucr1;
+	u32 ucr1, ucr4;

 	/* clear UCR1 */
 	ucr1 = imx_uart_readl(sport, UCR1);
 	ucr1 &= ~(UCR1_RXDMAEN | UCR1_TXDMAEN | UCR1_ATDMAEN);
 	imx_uart_writel(sport, ucr1, UCR1);

+	ucr4 = imx_uart_readl(sport, UCR4);
+	ucr4 &= ~UCR4_IDDMAEN;
+	imx_uart_writel(sport, ucr4, UCR4);
+
 	imx_uart_setup_ufcr(sport, TXTL_DEFAULT, RXTL_DEFAULT);

 	sport->dma_is_enabled = 0;
--
2.7.4

--
Pengutronix e.K.                           | Uwe Kleine-König
|
Industrial Linux Solutions                 |
https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.
pengutronix.de%2F&data=02%7C01%7Cyibin.gong%40nxp.com%7Cebbc2
26ea12d4f6dd93b08d61ece6add%7C686ea1d3bc2b4c6fa92cd99c5c301635%7
C0%7C0%7C636730269265048370&sdata=7NstF74mOGOFajEwFjBw7FAh
h3JdvGAIC9nliwrsf0Y%3D&reserved=0  |