[PATCH 04/15] tty: serial: 8250_core: read only RX if there is something in the FIFO
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: 2014-08-15 17:44:10
Also in:
linux-arm-kernel, linux-omap, lkml
Subsystem:
8250/16?50 (and clone uarts) serial driver, the rest, tty layer and serial drivers · Maintainers:
Greg Kroah-Hartman, Linus Torvalds, Jiri Slaby
The serial8250_do_startup() function unconditionally clears the interrupts and for that it reads from the RX-FIFO without checking if there is a byte in the FIFO or not. This works fine on OMAP4+ HW like AM335x or DRA7. OMAP3630 ES1.1 (which means probably all OMAP3 and earlier) does not like this: |Unhandled fault: external abort on non-linefetch (0x1028) at 0xfb020000 |Internal error: : 1028 [#1] ARM |Modules linked in: |CPU: 0 PID: 1 Comm: swapper Not tainted 3.16.0-00022-g7edcb57-dirty #1213 |task: de0572c0 ti: de058000 task.ti: de058000 |PC is at mem32_serial_in+0xc/0x1c |LR is at serial8250_do_startup+0x220/0x85c |Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment kernel |Control: 10c5387d Table: 80004019 DAC: 00000015 |[<c03051d4>] (mem32_serial_in) from [<c0307fe8>] (serial8250_do_startup+0x220/0x85c) |[<c0307fe8>] (serial8250_do_startup) from [<c0309e00>] (omap_8250_startup+0x5c/0xe0) |[<c0309e00>] (omap_8250_startup) from [<c030863c>] (serial8250_startup+0x18/0x2c) |[<c030863c>] (serial8250_startup) from [<c030394c>] (uart_startup+0x78/0x1d8) |[<c030394c>] (uart_startup) from [<c0304678>] (uart_open+0xe8/0x114) |[<c0304678>] (uart_open) from [<c02e9e10>] (tty_open+0x1a8/0x5a4) Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- drivers/tty/serial/8250/8250_core.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index ae268e3..cc90c19 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c@@ -2087,8 +2087,8 @@ int serial8250_do_startup(struct uart_port *port) /* * Clear the interrupt registers. */ - serial_port_in(port, UART_LSR); - serial_port_in(port, UART_RX); + if (serial_port_in(port, UART_LSR) & UART_LSR_DR) + serial_port_in(port, UART_RX); serial_port_in(port, UART_IIR); serial_port_in(port, UART_MSR);
@@ -2249,8 +2249,8 @@ int serial8250_do_startup(struct uart_port *port) * saved flags to avoid getting false values from polling * routines or the previous session. */ - serial_port_in(port, UART_LSR); - serial_port_in(port, UART_RX); + if (serial_port_in(port, UART_LSR) & UART_LSR_DR) + serial_port_in(port, UART_RX); serial_port_in(port, UART_IIR); serial_port_in(port, UART_MSR); up->lsr_saved_flags = 0;
@@ -2344,7 +2344,8 @@ void serial8250_do_shutdown(struct uart_port *port) * Read data port to reset things, and then unlink from * the IRQ chain. */ - serial_port_in(port, UART_RX); + if (serial_port_in(port, UART_LSR) & UART_LSR_DR) + serial_port_in(port, UART_RX); serial8250_rpm_put(up); del_timer_sync(&up->timer);
--
2.0.1