This is a note to let you know that I've just added the patch titled
serial: fsl_lpuart: avoid new transfer while DMA is running
to my tty git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-testing branch.
The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)
The patch will be merged to the tty-next branch sometime soon,
after it passes testing, and the merge window is open.
If you have any questions about this process, please let me know.
>From d3591f081b691a907835d121075226655ccec772 Mon Sep 17 00:00:00 2001
From: Stefan Agner <stefan@xxxxxxxx>
Date: Sat, 10 Jan 2015 01:08:59 +0100
Subject: serial: fsl_lpuart: avoid new transfer while DMA is running
When the UART is in DMA receive mode (RDMAS set) and one character
just arrived while another interrupt is handled (e.g. TX), the RDRF
(receiver data register full flag) is set due to the water level of
1. But since the DMA will take care of this character, there is no
need to handle it by calling lpuart_prepare_rx. Handling it leads to
adding the RX timeout timer twice:
[ 74.336698] Kernel BUG at 80053070 [verbose debug info unavailable]
[ 74.342999] Internal error: Oops - BUG: 0 [#1] ARM0:00.00 khungtaskd
[ 74.347817] Modules linked in: 0 S 0.0 0.0 0:00.00 writeback
[ 74.350926] CPU: 0 PID: 0 Comm: swapper Not tainted 3.19.0-rc3-00001-g39d78e2 #1788
[ 74.358617] Hardware name: Freescale Vybrid VF610 (Device Tree)t
[ 74.364563] task: 807a7678 ti: 8079c000 task.ti: 8079c000 kblockd
[ 74.370002] PC is at add_timer+0x24/0x28.0 0.0 0:00.09 kworker/u2:1
[ 74.373960] LR is at lpuart_int+0x15c/0x3d8
[ 74.378171] pc : [<80053070>] lr : [<802e0d88>] psr: a0010193
[ 74.378171] sp : 8079de10 ip : 8079de20 fp : 8079de1c
[ 74.389694] r10: 807d44c0 r9 : 8688c300 r8 : 00000013
[ 74.394943] r7 : 20010193 r6 : 00000000 r5 : 000000a0 r4 : 86997210
[ 74.401498] r3 : ffffa7da r2 : 80817868 r1 : 86997210 r0 : 86997344
[ 74.408052] Flags: NzCv IRQs off FIQs on Mode SVC_32 ISA ARM Segment kernel
[ 74.415489] Control: 10c5387d Table: 8611c059 DAC: 00000015
[ 74.421265] Process swapper (pid: 0, stack limit = 0x8079c230)
...
Solve this by only execute the receiver path (lpuart_prepare_rx) if
the DMA receive mode (RDMAS) is not set. Also, make sure the flag is
cleared on initialization, in case it has been left set.
This can be best reproduced using UART as a serial console, then
running top while dd'ing data into the terminal.
Signed-off-by: Stefan Agner <stefan@xxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx> # 3.14
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/serial/fsl_lpuart.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 29932b73c004..e95c4971327b 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -755,18 +755,18 @@ out:
static irqreturn_t lpuart_int(int irq, void *dev_id)
{
struct lpuart_port *sport = dev_id;
- unsigned char sts;
+ unsigned char sts, crdma;
sts = readb(sport->port.membase + UARTSR1);
+ crdma = readb(sport->port.membase + UARTCR5);
- if (sts & UARTSR1_RDRF) {
+ if (sts & UARTSR1_RDRF && !(crdma & UARTCR5_RDMAS)) {
if (sport->lpuart_dma_use)
lpuart_prepare_rx(sport);
else
lpuart_rxint(irq, dev_id);
}
- if (sts & UARTSR1_TDRE &&
- !(readb(sport->port.membase + UARTCR5) & UARTCR5_TDMAS)) {
+ if (sts & UARTSR1_TDRE && !(crdma & UARTCR5_TDMAS)) {
if (sport->lpuart_dma_use)
lpuart_pio_tx(sport);
else
@@ -1106,6 +1106,7 @@ static int lpuart_startup(struct uart_port *port)
setup_timer(&sport->lpuart_timer, lpuart_timer_func,
(unsigned long)sport);
temp = readb(port->membase + UARTCR5);
+ temp &= ~UARTCR5_RDMAS;
writeb(temp | UARTCR5_TDMAS, port->membase + UARTCR5);
}
--
2.2.2
--
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