On Thu, Jun 06, 2019 at 02:09:19PM +1000, Alexey Kardashevskiy wrote: > The pseries guests do not normally allocate PCI resouces and rely on > the system firmware doing so. Furthermore at least at some point in > the past the pseries guests won't even be allowed to change BARs, probably > it is still the case for phyp. So since the initial commit we have [1] > which prevents resource reallocation. > > This is not a problem until we want specific BAR alignments, for example, > PAGE_SIZE==64k to make sure we can still map MMIO BARs directly. For > the boot time devices we handle this in SLOF [2] but since QEMU's RTAS > does not allocate BARs, the guest does this instead and does not align > BARs even if Linux is given pci=resource_alignment=16@pci:0:0 as > PCI_PROBE_ONLY makes Linux ignore alignment requests. > > ARM folks added a dial to control PCI_PROBE_ONLY via the device tree [3]. > This makes use of the dial to advertise to the guest that we can handle > BAR reassignments. > > We do not remove the flag from [1] as pseries guests are still supported > under phyp so having that removed may cause problems. > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/platforms/pseries/setup.c?h=v5.1#n773 > [2] > https://git.qemu.org/?p=SLOF.git;a=blob;f=board-qemu/slof/pci-phb.fs;h=06729bcf77a0d4e900c527adcd9befe2a269f65d;hb=HEAD#l338 > [3] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f81c11af > Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>
Changing a guest visible property, that could have a big effect on how
the guest behaves, without a machine version change seems... unwise.
> ---
> hw/ppc/spapr.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 6dd8aaac3340..84d16f9edaca 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1209,6 +1209,9 @@ static void spapr_dt_chosen(SpaprMachineState *spapr,
> void *fdt)
> _FDT(fdt_setprop_string(fdt, chosen, "stdout-path", stdout_path));
> }
>
> + /* We can deal with BAR reallocation just fine, advertise it to the
> guest */
> + _FDT(fdt_setprop_cell(fdt, chosen, "linux,pci-probe-only", 0));
> +
> spapr_dt_ov5_platform_support(spapr, fdt, chosen);
>
> g_free(stdout_path);
--
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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