Re: [PULL v2 75/86] include/hw/pci/pcie_host: Correct PCIE_MMCFG_SIZE_MAX

[BALATON Zoltan]

On Thu, 26 May 2022, BALATON Zoltan wrote:
> Hello,
>
> On Thu, 26 May 2022, Daniel Henrique Barboza wrote:
> > Hi,
> >
> > This patch broke the boot of the sam460ex ppc machine:
> >
> > qemu-system-ppc -M sam460ex -kernel 
> > ./buildroot/qemu_ppc_sam460ex-latest/vmlinux \
> > -device virtio-net-pci,netdev=net0 -netdev user,id=net0 -serial mon:stdio \
> > -nographic -snapshot
> > qemu-system-ppc: ../hw/pci/pcie_host.c:97: pcie_host_mmcfg_init: Assertion 
> > `size <= PCIE_MMCFG_SIZE_MAX' failed.

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

(gdb) bt
#0  0x00007ffff68ff4a0 in raise () at /lib64/libc.so.6
#1  0x00007ffff68ea536 in abort () at /lib64/libc.so.6
#2  0x00007ffff68ea42f in _nl_load_domain.cold () at /lib64/libc.so.6
#3  0x00007ffff68f7ed2 in  () at /lib64/libc.so.6
#4  0x000055555596646f in pcie_host_mmcfg_init (e=e@entry=0x5555567942f0, 
size=size@entry=0x20000000) at ../hw/pci/pcie_host.c:97
#5  0x000055555596653b in pcie_host_mmcfg_map (size=0x20000000, 
addr=0xd20000000, e=0x5555567942f0) at ../hw/pci/pcie_host.c:105
#6  pcie_host_mmcfg_update (e=0x5555567942f0, enable=0x1, addr=0xd20000000, 
size=0x20000000) at ../hw/pci/pcie_host.c:118
#7  0x0000555555a70d7c in ppc_dcr_write (dcr_env=0x555556669c10, dcrn=0x122, 
val=0xe0000001) at ../hw/ppc/ppc.c:1418
#8  0x0000555555abdabb in helper_store_dcr (env=0x555556633360, dcrn=0x122, 
val=0xe0000001) at ../target/ppc/timebase_helper.c:188

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#l963

when trying to map config space. Here the size is calculated as 0x20000000 
which does not fit the assert. I'm not sure what this means though and 
where is the problem. Any ideas?

Regards,
BALATON Zoltan

> Thanks for noticing this. I usually only test it during the freeze. Wasn't 
> there a test patch submitted by Philippe before? Isn't that yet merged or 
> included in CI? That should catch these before breaking it.
>
> > The reason is that it changed commit 58d5b22bbd5 ("ppc4xx: Add device 
> > models found in PPC440 core SoCs")) in a way that it wasn't expected by the 
> > board. The code seems to believe that, for a reason that isn't stated in 
> > the 58d5b22bbd5 commit message, PCIE_MMCFG_SIZE_MAX must be set to 1 << 29.
> >
> > I'm CCing BALATON Zoltan since he's the author of 58d5b22bbd5 and can 
> > provide context of his initial change and why the board seems to rely on 
> > it. qemu-ppc is being CCed for awareness of the sam460ex problem.
>
> I'm afraid I don't remember but maybe I did not have a definitive answer even 
> back then as the docs for this PCIe controller were not available so I've 
> mostly worked from docs for similar SoCs and U-Boot and Linux sources so 
> there were a lot of guessing. Maybe it's related to that the board maps 
> peripheral addresses above 4GB as the first 4GB is reserved for memory? Or 
> maybe there's some mixup between address spaces and the PCIe controller 
> should have a separate address space that's mapped in the system? I did not 
> have any knowledge about this back then and my understanding may still be 
> lacking on how this should work.
>
> > Zoltan, I wasn't able to amend to quickly amend the code in a way that I 
> > could preserve the current PCIE_MMCFG_SIZE_MAX setting and make sam460ex 
> > work again. Can you please take a look?
>
> The PCIe controllers of the 460EX are implemented at the end of 
> hw/ppc/ppc440_uc.c (a lot of these 4xx SoCs are sharing components and the 
> code organisation is a bit messy). As the comment near it says it's not 
> really fully tested and working. only good enough for firmware and OSes get 
> past testing it. I think trying to attach any device to it probably would 
> fail or I would be surprised if the OS could actually talk to it as there may 
> be some missing parts. So I'm happy with any solution that keeps the current 
> state of being able to boot the OSes running on it (some of which like 
> AmigaOS and MorphOS are closed source though so I don't know what their 
> drivers need; closest open source OS to them is AROS but not sure that's 
> working on real hardware). Some advice from somebody more knowledgeable about 
> PCIe emulation in QEMU would be welcome here.
>
> Regards,
> BALATON Zoltan
>
> > Thanks,
> >
> >
> > Daniel
> >
> >
> >
> > On 5/16/22 17:55, Michael S. Tsirkin wrote:
> > > From: Francisco Iglesias <frasse.iglesias@gmail.com>
> > >
> > > According to 7.2.2 in [1] bit 27 is the last bit that can be part of the
> > > bus number, this makes the ECAM max size equal to '1 << 28'. This patch
> > > restores back this value into the PCIE_MMCFG_SIZE_MAX define (which was
> > > changed in commit 58d5b22bbd5 ("ppc4xx: Add device models found in PPC440
> > > core SoCs")).
> > >
> > > [1] PCI Express® Base Specification Revision 5.0 Version 1.0
> > >
> > > Signed-off-by: Francisco Iglesias <frasse.iglesias@gmail.com>
> > > Message-Id: <20220411221836.17699-3-frasse.iglesias@gmail.com>
> > > Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > ---
> > >   include/hw/pci/pcie_host.h | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/include/hw/pci/pcie_host.h b/include/hw/pci/pcie_host.h
> > > index b3c8ce973c..82d92177da 100644
> > > --- a/include/hw/pci/pcie_host.h
> > > +++ b/include/hw/pci/pcie_host.h
> > > @@ -65,7 +65,7 @@ void pcie_host_mmcfg_update(PCIExpressHost *e,
> > >    * bit 12 - 14: function number
> > >    * bit  0 - 11: offset in configuration space of a given device
> > >    */
> > > -#define PCIE_MMCFG_SIZE_MAX             (1ULL << 29)
> > > +#define PCIE_MMCFG_SIZE_MAX             (1ULL << 28)
> > >   #define PCIE_MMCFG_SIZE_MIN             (1ULL << 20)
> > >   #define PCIE_MMCFG_BUS_BIT              20
> > >   #define PCIE_MMCFG_BUS_MASK             0xff