Re: [OpenBIOS] sbus slot probing

[Mark Cave-Ayland]

On 15/08/11 16:01, Bob Breuer wrote:
> Here's a preliminary patch for sbus slot probing.

Great work indeed :)
> This can be used for the preliminary dbri device patch, see my dbri-pre1
> branch at github: https://github.com/breuerr/qemu/tree/dbri-pre1
> That branch also has a rewritten fcode rom to avoid the use of the
> obsolete intr forth word.  Use the SS-20 machine to get the dbri device.
>
> Todo:
>    non-faulting reads so that an empty slot can be probed
>    extend to probe other (all?) slots as well
>    only add the slot E range for SS-20, but not SS-10
>
> Is there any existing code for sparc32 which does a non-faulting read?  It
> looks like even cpeek doesn't try to catch any faults.

Not that I know of. It looks as if there may be some work that needs to 
be done in qemu in order for this to happen as per the comment in 
hw/sun4m_iommu.c:

case IOMMU_ARBEN:
         // XXX implement SBus probing: fault when reading unmapped
         // addresses, fault cause and address stored to MMU/IOMMU
         s->regs[saddr] = (val & IOMMU_ARBEN_MASK) | IOMMU_MID;
         break;

I have a feeling that qemu invokes a known trap for unmapped memory, so 
it could be that given we know the SBus range we could just assume that 
any traps occurring during a read to that range is a failed probe?
> Bob
> Index: drivers/sbus.c
>
> --- drivers/sbus.c	(revision 1046)
> +++ drivers/sbus.c	(working copy)
> @@ -451,11 +451,36 @@
>   static void
>   sbus_probe_slot_ss10(unsigned int slot, uint64_t base)
>   {
> ucell fcode;
> unsigned char start;
> // OpenBIOS and Qemu don't know how to do Sbus probing
> switch(slot) {
> case 2: // SUNW,tcx
>     ob_tcx_init(slot, "/iommu/sbus/SUNW,tcx");
>     break;
> case 0xe: // dbri
>    fcode = ofmem_map_io(base, 0x1000);
>    // TODO: non-faulting read
>    start = *(unsigned char*)fcode;
>    if (start == 0xfd || start == 0xf1) {

See is_fcode() in libopenbios/fcode_load.c.
>        push_str("/iommu/sbus");
>        fword("select-dev");
>        fword("new-device");
>        push_str(NULL);
>        PUSH(0);    // offset
>        PUSH(slot); // space
>        push_str("encode-unit");
>        fword("$call-parent");
>        fword("set-args");
>        PUSH(fcode);
>        PUSH(1);
>        fword("byte-load");
>        fword("finish-device");
>        fword("unselect-dev");
>    }
>    ofmem_unmap(fcode, 0x1000);
>    break;
> case 0xf: // le, esp, bpp, power-management
>     ob_macio_init(slot, base, 0);
>     // Power management (APC) XXX should not exist
>
> @@ -534,6 +559,7 @@
>       { 1, 0, 0xe10000000ULL, 0x10000000,},
>       { 2, 0, 0xe20000000ULL, 0x10000000,},
>       { 3, 0, 0xe30000000ULL, 0x10000000,},
> [0xe] = { 0xe, 0, 0xee0000000ULL, 0x10000000,},
>  [0xf] = { 0xf, 0, 0xef0000000ULL, 0x10000000,},
> };

The only other thing I'd like to see, as you mention, is the probe moved 
into a separate function which can be called from the appropriate 
_init() functions. I'd be interested to follow the discussion related to 
handling the various traps that occur during a fault access on this 
thread as you progress.

ATB,

Mark.