Re: [Qemu-devel] [Qemu-ppc] [PATCH qemu v13 02/16] spapr_pci: Move DMA window enablement to a helper

[Alexey Kardashevskiy]

On 03/03/2016 12:40 PM, David Gibson wrote:
> On Tue, Mar 01, 2016 at 08:10:27PM +1100, Alexey Kardashevskiy wrote:
> > We are going to have multiple DMA windows soon so let's start preparing.
> >
> > This adds a new helper to create a DMA window and makes use of it in
> > sPAPRPHBState::realize().
> >
> > Signed-off-by: Alexey Kardashevskiy <address@hidden>
> > ---
> >   hw/ppc/spapr_pci.c | 40 +++++++++++++++++++++++++++-------------
> >   1 file changed, 27 insertions(+), 13 deletions(-)
> >
> > diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> > index 3d1145e..248f20a 100644
> > --- a/hw/ppc/spapr_pci.c
> > +++ b/hw/ppc/spapr_pci.c
> > @@ -803,6 +803,29 @@ static char *spapr_phb_get_loc_code(sPAPRPHBState *sphb, 
> > PCIDevice *pdev)
> >       return buf;
> >   }
> >
> > +static int spapr_phb_dma_window_enable(sPAPRPHBState *sphb,
> > +                                       uint32_t liobn, uint32_t page_shift,
> > +                                       uint64_t window_addr,
> > +                                       uint64_t window_size)
> > +{
> > +    sPAPRTCETable *tcet;
> > +    uint32_t nb_table = window_size >> page_shift;
> > +
> > +    if (!nb_table) {
> > +        return -1;
> > +    }
>
> The caller shouldn't do this, so this probably makes more sense as an
> assert() than an error return.


@dma_win_size is a PHB property so the cli can set it to zero - where is it 
supposed to fail? When DMA won't work? This will be not really obvious for 
the user. Check dma_win_size==0 where we check mem_win_addr/...?

> > +
> > +    tcet = spapr_tce_new_table(DEVICE(sphb), liobn, window_addr,
> > +                               page_shift, nb_table, false);
> > +    if (!tcet) {
> > +        return -1;
> > +    }
>
> Since you're adding error reporting, you might as well make it via the
> error API instead of a return code.  That way if we wasnt to add more
> detailed error API reporting to spapr_tce_new_table() in future,
> there's less to change.

Well, the table allocation is the only real thing which may fail there and 
spapr_phb_realize() does not pass Error to the callers so 
spapr_phb_dma_window_enable() would be the first one to propagate an error 
and it just seems a bit over engineered. Should I still do that?


> > +
> > +    memory_region_add_subregion(&sphb->iommu_root, tcet->bus_offset,
> > +                                spapr_tce_get_iommu(tcet));
> > +    return 0;
> > +}
> > +
> >   /* Macros to operate with address in OF binding to PCI */
> >   #define b_x(x, p, l)    (((x) & ((1<<(l))-1)) << (p))
> >   #define b_n(x)          b_x((x), 31, 1) /* 0 if relocatable */
> > @@ -1228,8 +1251,6 @@ static void spapr_phb_realize(DeviceState *dev, Error 
> > **errp)
> >       int i;
> >       PCIBus *bus;
> >       uint64_t msi_window_size = 4096;
> > -    sPAPRTCETable *tcet;
> > -    uint32_t nb_table;
> >
> >       if (sphb->index != (uint32_t)-1) {
> >           hwaddr windows_base;
> > @@ -1381,18 +1402,11 @@ static void spapr_phb_realize(DeviceState *dev, Error 
> > **errp)
> >           }
> >       }
> >
> > -    nb_table = sphb->dma_win_size >> SPAPR_TCE_PAGE_SHIFT;
> > -    tcet = spapr_tce_new_table(DEVICE(sphb), sphb->dma_liobn,
> > -                               0, SPAPR_TCE_PAGE_SHIFT, nb_table, false);
> > -    if (!tcet) {
> > -        error_setg(errp, "Unable to create TCE table for %s",
> > -                   sphb->dtbusname);
> > -        return;
> > -    }
> > -
> >       /* Register default 32bit DMA window */
> > -    memory_region_add_subregion(&sphb->iommu_root, sphb->dma_win_addr,
> > -                                spapr_tce_get_iommu(tcet));
> > +    if (spapr_phb_dma_window_enable(sphb, sphb->dma_liobn, 
> > SPAPR_TCE_PAGE_SHIFT,
> > +                                    sphb->dma_win_addr, sphb->dma_win_size)) {
> > +        error_setg(errp, "Unable to create TCE table for %s", sphb->dtbusname);
> > +    }
> >
> >       sphb->msi = g_hash_table_new_full(g_int_hash, g_int_equal, g_free, 
> > g_free);
> >   }


--
Alexey