From mboxrd@z Thu Jan 1 00:00:00 1970 From: bigeasy@linutronix.de (Sebastian Andrzej Siewior) Date: Wed, 10 Sep 2014 21:29:58 +0200 Subject: [PATCH 03/16] tty: serial: 8250_core: read only RX if there is something in the FIFO In-Reply-To: <1410377411-26656-1-git-send-email-bigeasy@linutronix.de> References: <1410377411-26656-1-git-send-email-bigeasy@linutronix.de> Message-ID: <1410377411-26656-4-git-send-email-bigeasy@linutronix.de> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Archived-At: List-Archive: List-Post: 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 |[] (mem32_serial_in) from [] (serial8250_do_startup+0x220/0x85c) |[] (serial8250_do_startup) from [] (omap_8250_startup+0x5c/0xe0) |[] (omap_8250_startup) from [] (serial8250_startup+0x18/0x2c) |[] (serial8250_startup) from [] (uart_startup+0x78/0x1d8) |[] (uart_startup) from [] (uart_open+0xe8/0x114) |[] (uart_open) from [] (tty_open+0x1a8/0x5a4) Reviewed-by: Tony Lindgren Tested-by: Tony Lindgren Signed-off-by: Sebastian Andrzej Siewior --- 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 3cf5c98013e4..547afde9fdda 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -2088,8 +2088,8 @@ 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); @@ -2250,8 +2250,8 @@ 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); -- 2.1.0