Re: [Qemu-devel] [PATCH v3 07/10] ppc/pnv: add XSCOM infrastructure

[David Gibson]

On Mon, Sep 26, 2016 at 06:11:36PM +0200, Cédric Le Goater wrote:
> On 09/23/2016 04:46 AM, David Gibson wrote:
> > On Thu, Sep 22, 2016 at 10:25:59AM +0200, Cédric Le Goater wrote:
> >>>> @@ -493,6 +525,8 @@ static void pnv_chip_power9_class_init(ObjectClass 
> >>>> *klass, void *data)
> >>>>      k->chip_cfam_id = 0x100d104980000000ull; /* P9 Nimbus DD1.0 */
> >>>>      k->cores_mask = POWER9_CORE_MASK;
> >>>>      k->core_pir = pnv_chip_core_pir_p9;
> >>>> +    k->xscom_addr = pnv_chip_xscom_addr_p9;
> >>>> +    k->xscom_pcba = pnv_chip_xscom_pcba_p9;
> >>>
> >>> So if you do as BenH (and I) suggested and have the "scom address
> >>> space" actually be addressed by (pcba << 3), I think you can probably
> >>> avoid these.  
> >>
> >> I will look at that option again. 
> >>
> >> I was trying to untangle a few things at the same time. I have better
> >> view of the problem to solve now. The bus is gone, that's was one 
> >> thing. How we map these xscom regions is the next. 
> >>
> >> Ben suggested to add some P7/P8 mangling before the dispatch in 
> >> the &address_space_xscom. This should make things cleaner. I had 
> >> not thought of doing that and this is why I introduced these helpers :
> >>
> >> +uint32_t pnv_xscom_pcba(PnvXScomInterface *dev, uint64_t addr)
> >> +uint64_t pnv_xscom_addr(PnvXScomInterface *dev, uint32_t pcba)
> >>
> >> which I don't really like ...
> >>
> >> but we must make sure that we can do the mapping of the xscom 
> >> subregions in the &address_space_xscom using (pcba << 3)
> >>
> >>
> >>> Instead you can handle it in the chip or ADU realize function by either:
> >>>
> >>>     P8: * map one big subregion for the ADU into &address_space_memory
> >>>         * have the handler for that subregion do the address mangling,
> >>>           then redispatch into the xscom address space
> >>>
> >>>     P9: * Map the appropriate chunk of the xscom address space
> >>>           directly into address_space_memory
> >>
> >> Yes that was my feeling for a better solution but Ben chimed in with the 
> >> HMER topic. I need to look at that.
> > 
> > Right.  Doesn't change the basic concept though - it just means you
> > need (slightly different) redispatchers for both P8 and P9.
> 
> In fact they are the same, you only need an "addr to pcba" handler at the
> chip class level : 

Ok.  I'd been thinking of using different dispatchers as an
alternative to using the chip class translator hook, but I guess if
you have the decoding of those "core" registers here as well, then
that doesn't make so much sense.

> static uint64_t xscom_read(void *opaque, hwaddr addr, unsigned width)
> {
>       PnvChip *chip = opaque;
>       uint32_t pcba = PNV_CHIP_GET_CLASS(chip)->xscom_pcba(addr);
>       uint64_t val = 0;
>       MemTxResult result;
> 
>       ...
> 
>         val = address_space_ldq(&chip->xscom_as, pcba << 3,
>                                 MEMTXATTRS_UNSPECIFIED, &result);
>         if (result != MEMTX_OK) {
> 
>   
> 
> And so, the result is pretty clean. I killed the proxy object and merged 
> the regions in the chip but I have kept the pnv_xscom.c file because the 
> code related to xscom is rather large : ~250 lines. 

Sure, makes sense.

> The objects declaring a xscom region need to do some register shifting but 
> this is usual in mmio regions.
> 
> You will see in v4.

Ok.

> >>>> +static bool xscom_dispatch_read(PnvXScom *xscom, hwaddr addr, uint64_t 
> >>>> *val)
> >>>> +{
> >>>> +    uint32_t success;
> >>>> +    uint8_t data[8];
> >>>> +
> >>>> +    success = !address_space_rw(&xscom->xscom_as, addr, 
> >>>> MEMTXATTRS_UNSPECIFIED,
> >>>> +                                data, 8, false);
> >>>> +    *val = (((uint64_t) data[0]) << 56 |
> >>>> +            ((uint64_t) data[1]) << 48 |
> >>>> +            ((uint64_t) data[2]) << 40 |
> >>>> +            ((uint64_t) data[3]) << 32 |
> >>>> +            ((uint64_t) data[4]) << 24 |
> >>>> +            ((uint64_t) data[5]) << 16 |
> >>>> +            ((uint64_t) data[6]) << 8  |
> >>>> +            ((uint64_t) data[7]));
> >>>
> >>> AFAICT this is basically assuming data is always encoded BE.  With the
> >>> right choice of endian flags on the individual SCOM device
> >>> registrations with the scom address space, I think you should be able
> >>> to avoid this mangling.
> >>
> >> yes. I should but curiously I had to do this, and this works the same on
> >> an intel host or a ppc64 host.
> > 
> > Hmm.. I suspect what you actually need is NATIVE_ENDIAN on the
> > individual SCOM devices, with BIG_ENDIAN on the redispatcher region.
> 
> we should be using address_space_ldq and address_space_stq.

Ok.

> >>>> +
> >>>> +    success = !address_space_rw(&xscom->xscom_as, addr, 
> >>>> MEMTXATTRS_UNSPECIFIED,
> >>>> +                           data, 8, true);
> >>>> +    return success;
> >>>> +}
> >>>> +
> >>>> +static uint64_t xscom_read(void *opaque, hwaddr addr, unsigned width)
> >>>> +{
> >>>> +    PnvXScom *s = opaque;
> >>>> +    uint32_t pcba = s->chip_class->xscom_pcba(addr);
> >>>> +    uint64_t val = 0;
> >>>> +
> >>>> +    /* Handle some SCOMs here before dispatch */
> >>>> +    switch (pcba) {
> >>>> +    case 0xf000f:
> >>>> +        val = s->chip_class->chip_cfam_id;
> >>>> +        break;
> >>>> +    case 0x1010c00:     /* PIBAM FIR */
> >>>> +    case 0x1010c03:     /* PIBAM FIR MASK */
> >>>> +    case 0x2020007:     /* ADU stuff */
> >>>> +    case 0x2020009:     /* ADU stuff */
> >>>> +    case 0x202000f:     /* ADU stuff */
> >>>> +        val = 0;
> >>>> +        break;
> >>>> +    case 0x2013f00:     /* PBA stuff */
> >>>> +    case 0x2013f01:     /* PBA stuff */
> >>>> +    case 0x2013f02:     /* PBA stuff */
> >>>> +    case 0x2013f03:     /* PBA stuff */
> >>>> +    case 0x2013f04:     /* PBA stuff */
> >>>> +    case 0x2013f05:     /* PBA stuff */
> >>>> +    case 0x2013f06:     /* PBA stuff */
> >>>> +    case 0x2013f07:     /* PBA stuff */
> >>>> +        val = 0;
> >>>> +        break;
> >>>
> >>> It'd be theoretically nicer to actually register regions for these
> >>> special case addresses, but handling it here is a reasonable hack to
> >>> get things working quickly for the time being.
> >>
> >> I will make a default region on the whole xscomm address space to catch 
> >> these.
> > 
> > Ok.
> 
> Well, it does not bring much and we loose the ability to catch errors. 
> I will leave it that way.
> 
> Thanks,
> 
> C. 
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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