svn commit: r246016 - head/sys/dev/uart

[Ronald Klop]

On Mon, 28 Jan 2013 00:33:43 +0100, Colin Percival <cperciva at freebsd.org>  
wrote:

> Author: cperciva
> Date: Sun Jan 27 23:33:42 2013
> New Revision: 246016
> URL: http://svnweb.freebsd.org/changeset/base/246016
>
> Log:
>   Add a loader tunable "hw.broken_txfifo" which enables a workaround for  
> a
>   bug in old versions of QEMU (and Xen, and other places using QEMU  
> code).
>   On those buggy emulated UARTs, the "TX idle" interrupt gets lost; with
>   this workaround, we spinwait for the TX to happen and then send  
> ourselves
>   the interrupt.  It's ugly but it works, while minimizing the impact on
>   the code for the !broken_txfifo case.
>  MFC after:	2 weeks

Would hw.uart.broken_txfifo not be a better name?
It looks more in line with the other devices under hw.* and avoids naming  
collisions.

Regards,
Ronald.


>
> Modified:
>   head/sys/dev/uart/uart_dev_ns8250.c
>
> Modified: head/sys/dev/uart/uart_dev_ns8250.c
> ==============================================================================
> --- head/sys/dev/uart/uart_dev_ns8250.c	Sun Jan 27 23:21:51  
> 2013	(r246015)
> +++ head/sys/dev/uart/uart_dev_ns8250.c	Sun Jan 27 23:33:42  
> 2013	(r246016)
> @@ -31,6 +31,8 @@ __FBSDID("$FreeBSD$");
>  #include <sys/systm.h>
>  #include <sys/bus.h>
>  #include <sys/conf.h>
> +#include <sys/kernel.h>
> +#include <sys/sysctl.h>
>  #include <machine/bus.h>
> #include <dev/uart/uart.h>
> @@ -845,6 +847,11 @@ ns8250_bus_setsig(struct uart_softc *sc,
>  	return (0);
>  }
> +static int broken_txfifo = 0;
> +SYSCTL_INT(_hw, OID_AUTO, broken_txfifo, CTLFLAG_RW | CTLFLAG_TUN,
> +	&broken_txfifo, 0, "UART FIFO has QEMU emulation bug");
> +TUNABLE_INT("hw.broken_txfifo", &broken_txfifo);
> +
>  static int
>  ns8250_bus_transmit(struct uart_softc *sc)
>  {
> @@ -862,7 +869,12 @@ ns8250_bus_transmit(struct uart_softc *s
>  		uart_setreg(bas, REG_DATA, sc->sc_txbuf[i]);
>  		uart_barrier(bas);
>  	}
> -	sc->sc_txbusy = 1;
> +	if (broken_txfifo)
> +		ns8250_drain(bas, UART_DRAIN_TRANSMITTER);
> +	else
> +		sc->sc_txbusy = 1;
>  	uart_unlock(sc->sc_hwmtx);
> +	if (broken_txfifo)
> +		uart_sched_softih(sc, SER_INT_TXIDLE);
>  	return (0);
>  }
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