[Qemu-devel] spapr_pci: Advertise BAR reallocation capability

[Alexey Kardashevskiy]

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 address@hidden: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 <address@hidden>
---
 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);
-- 
2.17.1