linux-kernel - [PATCH] 8250: Hypervisors always export working 16550A UARTs.

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Date:	Thu, 28 Apr 2016 23:18:33 +0100
From:	"Richard W.M. Jones" <rjones@...hat.com>
To:	gregkh@...uxfoundation.org
Cc:	jslaby@...e.com, peter@...leysoftware.com,
	andriy.shevchenko@...ux.intel.com, phillip.raffeck@....de,
	anton.wuerfel@....de, yamada.masahiro@...ionext.com,
	matwey@....msu.ru, valentinrothberg@...il.com,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	ddutile@...hat.com
Subject: [PATCH] 8250: Hypervisors always export working 16550A UARTs.

Currently autoconf spends 25ms (on my laptop) testing if the UART
exported to it by KVM is an 8250 without FIFO and/or with strange
quirks, which it obviously isn't.  Assume it is exported to us by a
hypervisor, it's a normal, working 16550A.

Signed-off-by: Richard W.M. Jones <rjones@...hat.com>
---
 drivers/tty/serial/8250/8250_port.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 00ad2637..de19924 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1171,6 +1171,13 @@ static void autoconfig(struct uart_8250_port *up)
 	if (!port->iobase && !port->mapbase && !port->membase)
 		return;
 
+	/* Hypervisors always export working 16550A devices. */
+	if (cpu_has_hypervisor) {
+		up->port.type = PORT_16550A;
+		up->capabilities |= UART_CAP_FIFO;
+		return;
+	}
+
 	DEBUG_AUTOCONF("ttyS%d: autoconf (0x%04lx, 0x%p): ",
 		       serial_index(port), port->iobase, port->membase);
 
-- 
2.7.4