Re: [Qemu-devel] [PATCH 6/7] s390x/pci: move the memory region write from pcistg

[Pierre Morel]

On 10/11/2017 10:51, Cornelia Huck wrote:
> On Fri, 10 Nov 2017 17:40:12 +0800
> Yi Min Zhao <address@hidden> wrote:
>
> > 在 2017/11/10 上午3:23, Cornelia Huck 写道:
> > > On Tue,  7 Nov 2017 18:24:38 +0100
> > > Pierre Morel <address@hidden> wrote:
> > >   
> > > > Let's move the memory region write from pcistg into a dedicated
> > > > function.
> > > > This allows us to prepare a later patch searching for subregions
> > > > inside of the memory region.
> > > OK, so here is the memory region write. Do we have any sleeping
> > > endianness bugs in there for when we wire up tcg? I'm not sure how this
> > > plays with the bswaps (see patch 1).
> > >
> > > But maybe I've just gotten lost somewhere.
> > I think there's no error. For PCI bars' MRs, we got the little-endian data
> > that is exactly fit to the byte ordering of pcilg instruction. For PCI
> > config
> > space, the data has been swapped according to the cpu byte ordering.
>
> Host or target cpu?
>
> > So we use zpci_swap_endian() to swap the data back to the little-endian
> > ordering.

I do not see where we use the zpci_swap_endian() function in this patch 
or in the zpci_write_bar() function.

> That swap is unconditional. If we were running on a little-endian host,
> it would be wrong, wouldn't it?

I think there is no problem here, we do not use this function but we use 
the memory_region_dispatch_write() to access a subregion of the PCI 
device which is defined as DEVICE_LITTLE_ENDIAN

AFAIU The memory access process the endianness correctly.

> > >   
> > > > Signed-off-by: Pierre Morel <address@hidden>
> > > > Reviewed-by: Yi Min Zhao <address@hidden>
> > > > ---
> > > >    hw/s390x/s390-pci-inst.c | 27 +++++++++++++++++----------
> > > >    1 file changed, 17 insertions(+), 10 deletions(-)


--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany