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serial: 8250: Add flag so drivers can avoid THRE probe 

The probing of THRE irq behaviour assumes the other end will be reading
bytes out of the buffer in order to probe the port at driver init. In
some cases the other end cannot be relied upon to read these bytes, so
provide a flag for them to skip this step.

Bit 19 was chosen as the flags are a int and the top bits are taken.

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
hifive-unleashed-5.1
Joel Stanley 2017-05-02 17:15:42 +09:30 committed by Greg Kroah-Hartman
parent 70b2fe355a
commit ea5244e2af
2 changed files with 2 additions and 1 deletions
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2
drivers/tty/serial/8250/8250_port.c
View File

@ -2229,7 +2229,7 @@ int serial8250_do_startup(struct uart_port *port)
}
}
if (port->irq) {
if (port->irq && !(up->port.flags & UPF_NO_THRE_TEST)) {
unsigned char iir1;
/*
* Test for UARTs that do not reassert THRE when the

1
include/linux/serial_core.h
View File

@ -195,6 +195,7 @@ struct uart_port {
#define UPF_NO_TXEN_TEST ((__force upf_t) (1 << 15))
#define UPF_MAGIC_MULTIPLIER ((__force upf_t) ASYNC_MAGIC_MULTIPLIER /* 16 */ )
#define UPF_NO_THRE_TEST ((__force upf_t) (1 << 19))
/* Port has hardware-assisted h/w flow control */
#define UPF_AUTO_CTS ((__force upf_t) (1 << 20))
#define UPF_AUTO_RTS ((__force upf_t) (1 << 21))