tty: serial: 8250_core: read only RX if there is something in the FIFO
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) Reviewed-by: Tony Lindgren <tony@atomide.com> Tested-by: Tony Lindgren <tony@atomide.com> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -2088,8 +2088,8 @@ int serial8250_do_startup(struct uart_port *port)
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/*
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* Clear the interrupt registers.
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*/
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serial_port_in(port, UART_LSR);
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serial_port_in(port, UART_RX);
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if (serial_port_in(port, UART_LSR) & UART_LSR_DR)
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serial_port_in(port, UART_RX);
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serial_port_in(port, UART_IIR);
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serial_port_in(port, UART_MSR);
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@ -2250,8 +2250,8 @@ dont_test_tx_en:
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* saved flags to avoid getting false values from polling
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* routines or the previous session.
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*/
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serial_port_in(port, UART_LSR);
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serial_port_in(port, UART_RX);
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if (serial_port_in(port, UART_LSR) & UART_LSR_DR)
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serial_port_in(port, UART_RX);
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serial_port_in(port, UART_IIR);
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serial_port_in(port, UART_MSR);
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up->lsr_saved_flags = 0;
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@ -2344,7 +2344,8 @@ void serial8250_do_shutdown(struct uart_port *port)
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* Read data port to reset things, and then unlink from
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* the IRQ chain.
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*/
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serial_port_in(port, UART_RX);
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if (serial_port_in(port, UART_LSR) & UART_LSR_DR)
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serial_port_in(port, UART_RX);
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serial8250_rpm_put(up);
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del_timer_sync(&up->timer);
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