Re: [Qemu-devel] [PATCH] hw/arm/virt: mark the PCIe host controller as DMA coherent in the DT

[Andrew Jones]

On Thu, Jun 30, 2016 at 03:09:53PM +0100, Peter Maydell wrote:
> On 28 June 2016 at 18:14, Ard Biesheuvel <address@hidden> wrote:
> > Since QEMU performs cacheable accesses to guest memory when doing DMA
> > as part of the implementation of emulated PCI devices, guest drivers
> > should use cacheable accesses as well when running under KVM. Since this
> > essentially means that emulated PCI devices are DMA coherent, set the
> > 'dma-coherent' DT property on the PCIe host controller DT node.
> >
> > Signed-off-by: Ard Biesheuvel <address@hidden>
> > ---
> >  hw/arm/virt.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> > index c5c125e9204a..6e098afd1fe5 100644
> > --- a/hw/arm/virt.c
> > +++ b/hw/arm/virt.c
> > @@ -1021,6 +1021,7 @@ static void create_pcie(const VirtBoardInfo *vbi, 
> > qemu_irq *pic,
> >      qemu_fdt_setprop_cell(vbi->fdt, nodename, "#size-cells", 2);
> >      qemu_fdt_setprop_cells(vbi->fdt, nodename, "bus-range", 0,
> >                             nr_pcie_buses - 1);
> > +    qemu_fdt_setprop(vbi->fdt, nodename, "dma-coherent", NULL, 0);
> >
> >      if (vbi->v2m_phandle) {
> >          qemu_fdt_setprop_cells(vbi->fdt, nodename, "msi-parent",
> > --
> > 2.7.4
> 
> Applied, thanks.
> 
> -- PMM
>

I might have mentioned in the commit message that the ACPI generation
already does this, as _CCA is set to 1, added with commit bc64b96c
(assuming I'm right, and a value of 1 there is the ACPI equivalent of
 this patch)

bc64b96c's commit message is also lacking, in the fact it doesn't
state why the value of 1 is chosen, only that the attribute is
compulsory, which I presume could have been added with the value 0
to satisfy that.

Anyway, I just wanted to point out that I *think* we're fine for
ACPI. Perhaps I'm the only one who didn't know that already though...

Thanks,
drew