Re: [Qemu-devel] [PATCH for-1.6] mips_malta: do not raise exceptions when accessing invalid memory

[Stefan Weil <sw@weilnetz.de>]

Am 12.08.2013 21:44, schrieb Aurelien Jarno:
> Since commit c658b94f6e8c206c59d02aa6fbac285b86b53d2c, MIPS raises
> exceptions when accessing invalid memory. This is not the correct
> behaviour for MIPS Malta Core LV, as the GT-64120A system controller
> just ignore undecoded access. This feature is used by the Linux kernel
> to probe for some devices.
>
> Emulate the correct behaviour in QEMU by adding an empty slot covering
> the entire memory space decoded by the GT-64120A.
>
> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
> ---
>  default-configs/mips-softmmu.mak     |    1 +
>  default-configs/mips64-softmmu.mak   |    1 +
>  default-configs/mips64el-softmmu.mak |    1 +
>  default-configs/mipsel-softmmu.mak   |    1 +
>  hw/mips/mips_malta.c                 |    6 ++++++
>  5 files changed, 10 insertions(+)
>
> diff --git a/default-configs/mips-softmmu.mak b/default-configs/mips-softmmu.mak
> index 926709a..71177ef 100644
> --- a/default-configs/mips-softmmu.mak
> +++ b/default-configs/mips-softmmu.mak
> @@ -34,3 +34,4 @@ CONFIG_JAZZ_LED=y
>  CONFIG_MC146818RTC=y
>  CONFIG_VT82C686=y
>  CONFIG_ISA_TESTDEV=y
> +CONFIG_EMPTY_SLOT=y
> diff --git a/default-configs/mips64-softmmu.mak b/default-configs/mips64-softmmu.mak
> index 0ef3f09..617301b 100644
> --- a/default-configs/mips64-softmmu.mak
> +++ b/default-configs/mips64-softmmu.mak
> @@ -34,3 +34,4 @@ CONFIG_JAZZ_LED=y
>  CONFIG_MC146818RTC=y
>  CONFIG_VT82C686=y
>  CONFIG_ISA_TESTDEV=y
> +CONFIG_EMPTY_SLOT=y
> diff --git a/default-configs/mips64el-softmmu.mak b/default-configs/mips64el-softmmu.mak
> index 6089318..317b151 100644
> --- a/default-configs/mips64el-softmmu.mak
> +++ b/default-configs/mips64el-softmmu.mak
> @@ -36,3 +36,4 @@ CONFIG_JAZZ_LED=y
>  CONFIG_MC146818RTC=y
>  CONFIG_VT82C686=y
>  CONFIG_ISA_TESTDEV=y
> +CONFIG_EMPTY_SLOT=y
> diff --git a/default-configs/mipsel-softmmu.mak b/default-configs/mipsel-softmmu.mak
> index cd59e24..532a9ae 100644
> --- a/default-configs/mipsel-softmmu.mak
> +++ b/default-configs/mipsel-softmmu.mak
> @@ -34,3 +34,4 @@ CONFIG_JAZZ_LED=y
>  CONFIG_MC146818RTC=y
>  CONFIG_VT82C686=y
>  CONFIG_ISA_TESTDEV=y
> +CONFIG_EMPTY_SLOT=y
> diff --git a/hw/mips/mips_malta.c b/hw/mips/mips_malta.c
> index 0f5de33..61cb3e4 100644
> --- a/hw/mips/mips_malta.c
> +++ b/hw/mips/mips_malta.c
> @@ -50,6 +50,7 @@
>  #include "qemu/host-utils.h"
>  #include "sysemu/qtest.h"
>  #include "qemu/error-report.h"
> +#include "hw/empty_slot.h"
>  
>  //#define DEBUG_BOARD_INIT
>  
> @@ -908,6 +909,11 @@ void mips_malta_init(QEMUMachineInitArgs *args)
>      DeviceState *dev = qdev_create(NULL, TYPE_MIPS_MALTA);
>      MaltaState *s = MIPS_MALTA(dev);
>  
> +    /* The whole address space decoded by the GT-64120A doesn't generate
> +       exception when accessing invalid memory. Create an empty slot to
> +       emulate this feature. */
> +    empty_slot_init(0, 0x1fffffff);
> +
>      qdev_init_nofail(dev);
>  
>      /* Make sure the first 3 serial ports are associated with a device. */

Hello Aurelien,

the patch fixes Linux boot with Malta, therefore

Tested-by: Stefan Weil <sw@weilnetz.de>

The 2nd parameter of empty_slot_init is not the end address
but the length, so I think it should be 0x20000000. With this
modification, the patch is good for 1.6.

I did not find a hint in the GT-64120A documentation about
handling of addresses without connected devices. It is still
strange that the exception handler throws a secondary
exception with the current code.

Regards,
Stefan