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

From "Richard W.M. Jones" <rjones@redhat.com>
Newsgroups linux.kernel
Subject [PATCH] 8250: Hypervisors always export working 16550A UARTs.
Date 2016-04-29 00:20 +0200
Message-ID <rt2rU-3gl-11@gated-at.bofh.it> (permalink)
References <rt2rU-3gl-13@gated-at.bofh.it>
Organization linux.* mail to news gateway

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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@redhat.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

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[PATCH] 8250: Hypervisors always export working 16550A UARTs. "Richard W.M. Jones" <rjones@redhat.com> - 2016-04-29 00:20 +0200
  Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. Greg KH <gregkh@linuxfoundation.org> - 2016-04-29 01:00 +0200
    Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. "Richard W.M. Jones" <rjones@redhat.com> - 2016-04-29 10:20 +0200
      Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. Greg KH <gregkh@linuxfoundation.org> - 2016-04-29 17:20 +0200
        Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. "Richard W.M. Jones" <rjones@redhat.com> - 2016-04-29 17:40 +0200
          Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. Greg KH <gregkh@linuxfoundation.org> - 2016-04-29 18:00 +0200
            Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. "Richard W.M. Jones" <rjones@redhat.com> - 2016-04-29 18:10 +0200
              Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. Greg KH <gregkh@linuxfoundation.org> - 2016-04-29 19:40 +0200
          Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. Don Dutile <ddutile@redhat.com> - 2016-04-29 20:20 +0200

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