Re: [PATCH 06/21] q800: allow accesses to RAM area even if less memory is available

[Laurent Vivier <laurent@vivier.eu>]

Le 02/07/2023 à 17:48, Mark Cave-Ayland a écrit :
> MacOS attempts a series of writes and reads over the entire RAM area in order
> to determine the amount of RAM within the machine. Allow accesses to the
> entire RAM area ignoring writes and always reading zero for areas where there
> is no physical RAM installed to allow MacOS to detect the memory size without
> faulting.
> 
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> ---
>   hw/m68k/q800.c         | 30 +++++++++++++++++++++++++++++-
>   include/hw/m68k/q800.h |  1 +
>   2 files changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/m68k/q800.c b/hw/m68k/q800.c
> index 081b95e9cf..3209309173 100644
> --- a/hw/m68k/q800.c
> +++ b/hw/m68k/q800.c
> @@ -86,6 +86,9 @@
>   
>   #define MAC_CLOCK  3686418
>   
> +/* Size of whole RAM area */
> +#define RAM_SIZE              0x40000000
> +
>   /*
>    * Slot 0x9 is reserved for use by the in-built framebuffer whilst only
>    * slots 0xc, 0xd and 0xe physically exist on the Quadra 800
> @@ -218,6 +221,27 @@ static const MemoryRegionOps machine_id_ops = {
>       },
>   };
>   
> +static uint64_t ramio_read(void *opaque, hwaddr addr, unsigned size)
> +{
> +    return 0x0;
> +}
> +
> +static void ramio_write(void *opaque, hwaddr addr, uint64_t val,
> +                        unsigned size)
> +{
> +    return;
> +}
> +
> +static const MemoryRegionOps ramio_ops = {
> +    .read = ramio_read,
> +    .write = ramio_write,
> +    .endianness = DEVICE_BIG_ENDIAN,
> +    .valid = {
> +        .min_access_size = 1,
> +        .max_access_size = 4,
> +    },
> +};
> +
>   static void q800_machine_init(MachineState *machine)
>   {
>       Q800MachineState *m = Q800_MACHINE(machine);
> @@ -262,7 +286,11 @@ static void q800_machine_init(MachineState *machine)
>       qemu_register_reset(main_cpu_reset, &m->cpu);
>   
>       /* RAM */
> -    memory_region_add_subregion(get_system_memory(), 0, machine->ram);
> +    memory_region_init_io(&m->ramio, OBJECT(machine), &ramio_ops, &m->ramio,
> +                          "ram", RAM_SIZE);
> +    memory_region_add_subregion(get_system_memory(), 0x0, &m->ramio);
> +
> +    memory_region_add_subregion(&m->ramio, 0, machine->ram);
>   
>       /*
>        * Create container for all IO devices
> diff --git a/include/hw/m68k/q800.h b/include/hw/m68k/q800.h
> index 98097165d9..04e4e0bce3 100644
> --- a/include/hw/m68k/q800.h
> +++ b/include/hw/m68k/q800.h
> @@ -60,6 +60,7 @@ struct Q800MachineState {
>       MacfbNubusState macfb;
>       DJMEMCState djmemc;
>       IOSBState iosb;
> +    MemoryRegion ramio;
>       MemoryRegion macio;
>       MemoryRegion macio_alias;
>       MemoryRegion machine_id;

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