Re: [PATCH v4 08/20] nubus: generate bus error when attempting to access empty slots

[Laurent Vivier]

Le 17/09/2021 à 09:50, Mark Cave-Ayland a écrit :
> According to "Designing Cards and Drivers for the Macintosh Family" any 
> attempt
> to access an unimplemented address location on Nubus generates a bus error. 
> MacOS
> uses a custom bus error handler to detect empty Nubus slots, and with the 
> current
> implementation assumes that all slots are occupied as the Nubus transactions
> never fail.
> 
> Switch nubus_slot_ops and nubus_super_slot_ops over to use 
> {read,write}_with_attrs
> and hard-code them to return MEMTX_DECODE_ERROR so that unoccupied Nubus slots
> will generate the expected bus error.
> 
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>  hw/nubus/nubus-bus.c | 34 ++++++++++++++++++----------------
>  1 file changed, 18 insertions(+), 16 deletions(-)
> 
> diff --git a/hw/nubus/nubus-bus.c b/hw/nubus/nubus-bus.c
> index 39182db065..a617459a4f 100644
> --- a/hw/nubus/nubus-bus.c
> +++ b/hw/nubus/nubus-bus.c
> @@ -20,23 +20,23 @@ static NubusBus *nubus_find(void)
>      return NUBUS_BUS(object_resolve_path_type("", TYPE_NUBUS_BUS, NULL));
>  }
>  
> -static void nubus_slot_write(void *opaque, hwaddr addr, uint64_t val,
> -                             unsigned int size)
> +static MemTxResult nubus_slot_write(void *opaque, hwaddr addr, uint64_t val,
> +                                    unsigned size, MemTxAttrs attrs)
>  {
> -    /* read only */
>      trace_nubus_slot_write(addr, val, size);
> +    return MEMTX_DECODE_ERROR;
>  }
>  
> -static uint64_t nubus_slot_read(void *opaque, hwaddr addr,
> -                                unsigned int size)
> +static MemTxResult nubus_slot_read(void *opaque, hwaddr addr, uint64_t *data,
> +                                   unsigned size, MemTxAttrs attrs)
>  {
>      trace_nubus_slot_read(addr, size);
> -    return 0;
> +    return MEMTX_DECODE_ERROR;
>  }
>  
>  static const MemoryRegionOps nubus_slot_ops = {
> -    .read  = nubus_slot_read,
> -    .write = nubus_slot_write,
> +    .read_with_attrs  = nubus_slot_read,
> +    .write_with_attrs = nubus_slot_write,
>      .endianness = DEVICE_BIG_ENDIAN,
>      .valid = {
>          .min_access_size = 1,
> @@ -44,23 +44,25 @@ static const MemoryRegionOps nubus_slot_ops = {
>      },
>  };
>  
> -static void nubus_super_slot_write(void *opaque, hwaddr addr, uint64_t val,
> -                                   unsigned int size)
> +static MemTxResult nubus_super_slot_write(void *opaque, hwaddr addr,
> +                                          uint64_t val, unsigned size,
> +                                          MemTxAttrs attrs)
>  {
> -    /* read only */
>      trace_nubus_super_slot_write(addr, val, size);
> +    return MEMTX_DECODE_ERROR;
>  }
>  
> -static uint64_t nubus_super_slot_read(void *opaque, hwaddr addr,
> -                                      unsigned int size)
> +static MemTxResult nubus_super_slot_read(void *opaque, hwaddr addr,
> +                                         uint64_t *data, unsigned size,
> +                                         MemTxAttrs attrs)
>  {
>      trace_nubus_super_slot_read(addr, size);
> -    return 0;
> +    return MEMTX_DECODE_ERROR;
>  }
>  
>  static const MemoryRegionOps nubus_super_slot_ops = {
> -    .read  = nubus_super_slot_read,
> -    .write = nubus_super_slot_write,
> +    .read_with_attrs = nubus_super_slot_read,
> +    .write_with_attrs = nubus_super_slot_write,
>      .endianness = DEVICE_BIG_ENDIAN,
>      .valid = {
>          .min_access_size = 1,
> 

Reviewed-by: Laurent Vivier <laurent@vivier.eu>