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Commit 68af490b authored by Andy Shevchenko's avatar Andy Shevchenko Committed by Greg Kroah-Hartman
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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: default avatarPeter Hurley <peter@hurleysoftware.com>
Reviewed-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: default avatarBryan O'Donoghue <pure.logic@nexus-software.ie>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d1834bab

drivers/tty/serial/8250/8250_port.c

+3 −6
Original line number Diff line number Diff line
@@ -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;