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serial: 8250: enable AFE on ports where FIFO is 16 bytes 

Intel Quark has 16550A compatible UART with autoflow feature enabled. It has
only 16 bytes of FIFO. Currently serial8250_do_set_termios() prevents to enable
autoflow since the minimum requirement of 32 bytes of FIFO size.

Drop a FIFO size limitation to allow autoflow control be enabled on such UARTs.

While here, comment out UART_CAP_AFE for PORT_AR7 since it wasn't working and
it will be not a good idea to use it in conjunction with trigger level of 1
byte.

Suggested-by: Peter Hurley <peter@hurleysoftware.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Bryan O'Donoghue <pure.logic@nexus-software.ie>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Andy Shevchenko 2016-08-17 19:20:26 +03:00 committed by Greg Kroah-Hartman
parent d1834babe4
commit 68af490b03
1 changed files with 3 additions and 6 deletions
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9
drivers/tty/serial/8250/8250_port.c
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@ -178,7 +178,7 @@ static const struct serial8250_config uart_config[] = {
.fifo_size = 16,
.tx_loadsz = 16,
.fcr = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_00,
.flags = UART_CAP_FIFO | UART_CAP_AFE,
.flags = UART_CAP_FIFO /* | UART_CAP_AFE */,
},
[PORT_U6_16550A] = {
.name = "U6_16550A",
@ -2549,12 +2549,9 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
/*
* MCR-based auto flow control. When AFE is enabled, RTS will be
* deasserted when the receive FIFO contains more characters than
* the trigger, or the MCR RTS bit is cleared. In the case where
* the remote UART is not using CTS auto flow control, we must
* have sufficient FIFO entries for the latency of the remote
* UART to respond. IOW, at least 32 bytes of FIFO.
* the trigger, or the MCR RTS bit is cleared.
*/
if (up->capabilities & UART_CAP_AFE && port->fifosize >= 32) {
if (up->capabilities & UART_CAP_AFE) {
up->mcr &= ~UART_MCR_AFE;
if (termios->c_cflag & CRTSCTS)
up->mcr |= UART_MCR_AFE;