[PATCH] ppc: fix boot with sam460ex

["Michael S. Tsirkin" <mst@redhat.com>]

Recent changes to pcie_host corrected size of its internal region to
match what it expects - only the low 28 bits are ever decoded. Previous
code just ignored bit 29 (if size was 1 << 29) in the address which does
not make much sense.  We are now asserting on size > 1 << 28 instead,
but it so happened that ppc actually allows guest to configure as large
a size as it wants to, and current firmware set it to 1 << 29.

With just qemu-system-ppc -M sam460ex this triggers an assert which
seems to happen when the guest (board firmware?) writes a value to
CFGMSK reg:

(gdb) bt

This is done in the board firmware here:

https://git.qemu.org/?p=u-boot-sam460ex.git;a=blob;f=arch/powerpc/cpu/ppc4xx/4xx_pcie.c;h=13348be93dccc74c13ea043d6635a7f8ece4b5f0;hb=HEAD

when trying to map config space.

Note that what firmware does matches
https://www.hardware.com.br/comunidade/switch-cisco/1128380/

So it's not clear what the proper fix should be.

However, allowing guest to trigger an assert in qemu is not good practice anyway.

For now let's just force the mask to 256MB on guest write, this way
anything outside the expected address range is ignored.

Fixes: commit 1f1a7b2269 ("include/hw/pci/pcie_host: Correct PCIE_MMCFG_SIZE_MAX")
Reviewed-by: BALATON Zoltan <balaton@eik.bme.hu>
Tested-by: BALATON Zoltan <balaton@eik.bme.hu>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

Affected system is orphan so I guess I will merge the patch unless
someone objects.

 hw/ppc/ppc440_uc.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/hw/ppc/ppc440_uc.c b/hw/ppc/ppc440_uc.c
index 993e3ba955..a1ecf6dd1c 100644
--- a/hw/ppc/ppc440_uc.c
+++ b/hw/ppc/ppc440_uc.c
@@ -1180,6 +1180,14 @@ static void dcr_write_pcie(void *opaque, int dcrn, uint32_t val)
     case PEGPL_CFGMSK:
         s->cfg_mask = val;
         size = ~(val & 0xfffffffe) + 1;
+        /*
+         * Firmware sets this register to E0000001. Why we are not sure,
+         * but the current guess is anything above PCIE_MMCFG_SIZE_MAX is
+         * ignored.
+         */
+        if (size > PCIE_MMCFG_SIZE_MAX) {
+            size = PCIE_MMCFG_SIZE_MAX;
+        }
         pcie_host_mmcfg_update(PCIE_HOST_BRIDGE(s), val & 1, s->cfg_base, size);
         break;
     case PEGPL_MSGBAH:
-- 
MST