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Re: [PULL 70/73] hw/pxb-cxl: Support passthrough HDM Decoders unless ove
From: |
Jonathan Cameron |
Subject: |
Re: [PULL 70/73] hw/pxb-cxl: Support passthrough HDM Decoders unless overridden |
Date: |
Wed, 19 Apr 2023 14:57:54 +0100 |
On Tue, 11 Apr 2023 11:26:16 +0100
Peter Maydell <peter.maydell@linaro.org> wrote:
> On Wed, 8 Mar 2023 at 01:14, Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> >
> > The CXL r3.0 specification allows for there to be no HDM decoders on CXL
> > Host Bridges if they have only a single root port. Instead, all accesses
> > directed to the host bridge (as specified in CXL Fixed Memory Windows)
> > are assumed to be routed to the single root port.
>
> Hi; in issue https://gitlab.com/qemu-project/qemu/-/issues/1586
> it's been pointed out that this commit causes an assertion
> failure during 'make check' if you configure with
> --enable-qom-cast-debug. You can repro by doing that and running:
>
> qemu-system-i386 -display none -machine q35,cxl=on -device pxb-cxl,bus=pcie.0
>
> Here's a backtrace:
>
> Thread 1 "qemu-system-i38" received signal SIGABRT, Aborted.
> __pthread_kill_implementation (no_tid=0, signo=6,
> threadid=140737217810816) at ./nptl/pthread_kill.c:44
> 44 ./nptl/pthread_kill.c: No such file or directory.
> (gdb) bt
> #0 __pthread_kill_implementation (no_tid=0, signo=6,
> threadid=140737217810816) at ./nptl/pthread_kill.c:44
> #1 __pthread_kill_internal (signo=6, threadid=140737217810816) at
> ./nptl/pthread_kill.c:78
> #2 __GI___pthread_kill (threadid=140737217810816,
> signo=signo@entry=6) at ./nptl/pthread_kill.c:89
> #3 0x00007ffff4b1c476 in __GI_raise (sig=sig@entry=6) at
> ../sysdeps/posix/raise.c:26
> #4 0x00007ffff4b027f3 in __GI_abort () at ./stdlib/abort.c:79
> #5 0x0000555555cecfab in object_dynamic_cast_assert
> (obj=obj@entry=0x555557a70b60, typename=0x555555f80406 "pxb",
> file=0x555555f80357 "../../hw/pci-bridge/pci_expander_bridge.c",
> line=line@entry=55, func=0x555555f8040a "PXB_DEV") at
> ../../qom/object.c:890
> #6 0x00005555559c7bbd in PXB_DEV (obj=0x555557a70b60) at
> ../../hw/pci-bridge/pci_expander_bridge.c:54
> #7 pxb_cxl_dev_reset (dev=0x555557a70b60) at
> ../../hw/pci-bridge/pci_expander_bridge.c:314
> #8 0x00005555559bd624 in pci_qdev_realize (qdev=0x555557a70b60,
> errp=0x7fffffffdd28) at ../../hw/pci/pci.c:2098
> #9 0x0000555555ce8ada in device_set_realized (obj=<optimised out>,
> value=true, errp=0x7fffffffdea8) at ../../hw/core/qdev.c:510
> #10 0x0000555555cf0219 in property_set_bool
> (obj=obj@entry=0x555557a70b60, v=v@entry=0x555557a727b0,
> name=name@entry=0x55555601db04 "realized", opaque=0x55555687b780,
> errp=errp@entry=0x7fffffffdea8) at ../../qom/object.c:2285
> #11 0x0000555555cee4e5 in object_property_set
> (obj=obj@entry=0x555557a70b60, name=name@entry=0x55555601db04
> "realized", v=0x555557a727b0, errp=errp@entry=0x7fffffffdea8) at
> ../../qom/object.c:1420
> #12 0x0000555555cf23cd in object_property_set_qobject
> (obj=obj@entry=0x555557a70b60, name=name@entry=0x55555601db04
> "realized", value=<optimised out>, errp=errp@entry=0x7fffffffdea8) at
> ../../qom/qom-qobject.c:28
> #13 0x0000555555cee93b in object_property_set_bool
> (obj=0x555557a70b60, name=0x55555601db04 "realized", value=<optimised
> out>, errp=0x7fffffffdea8)
> at ../../qom/object.c:1489
> #14 0x0000555555a6ae42 in qdev_device_add_from_qdict
> (opts=0x555557a6fb40, from_json=false, errp=0x7fffffffdea8,
> errp@entry=0x555556765830 <error_fatal>)
> at ../../softmmu/qdev-monitor.c:714
> #15 0x0000555555a6b202 in qdev_device_add
> (opts=opts@entry=0x5555568776f0, errp=errp@entry=0x555556765830
> <error_fatal>) at ../../softmmu/qdev-monitor.c:733
> #16 0x0000555555a7367f in device_init_func (opaque=opaque@entry=0x0,
> opts=0x3cd16a, opts@entry=0x5555568776f0, errp=0x6,
> errp@entry=0x555556765830 <error_fatal>)
> at ../../softmmu/vl.c:1140
> #17 0x0000555555e78331 in qemu_opts_foreach
> (list=<optimised out>, func=0x555555a73670 <device_init_func>,
> opaque=opaque@entry=0x0, errp=0x555556765830 <error_fatal>) at
> ../../util/qemu-option.c:1135
> #18 0x0000555555a6dd61 in qemu_create_cli_devices () at
> ../../softmmu/vl.c:2542
> #19 qmp_x_exit_preconfig (errp=<optimised out>) at ../../softmmu/vl.c:2610
> #20 0x0000555555a7177b in qemu_init (argc=<optimised out>,
> argv=<optimised out>) at ../../softmmu/vl.c:3612
> #21 0x000055555587b656 in main (argc=3985770, argv=0x3cd16a) at
> ../../softmmu/main.c:47
>
> The problem is here:
>
> > -static void pxb_dev_reset(DeviceState *dev)
> > +static void pxb_cxl_dev_reset(DeviceState *dev)
>
> This function is called from pxb_cxl_dev_realize(),
> which is the realize function for TYPE_PXB_CXL_DEVICE.
> That type's parent is TYPE_PCI_DEVICE.
>
> > {
> > CXLHost *cxl = PXB_CXL_DEV(dev)->cxl.cxl_host_bridge;
> > CXLComponentState *cxl_cstate = &cxl->cxl_cstate;
> > + PCIHostState *hb = PCI_HOST_BRIDGE(cxl);
> > uint32_t *reg_state = cxl_cstate->crb.cache_mem_registers;
> > uint32_t *write_msk = cxl_cstate->crb.cache_mem_regs_write_mask;
> > + int dsp_count = 0;
> >
> > cxl_component_register_init_common(reg_state, write_msk,
> > CXL2_ROOT_PORT);
> > - ARRAY_FIELD_DP32(reg_state, CXL_HDM_DECODER_CAPABILITY, TARGET_COUNT,
> > 8);
> > + /*
> > + * The CXL specification allows for host bridges with no HDM decoders
> > + * if they only have a single root port.
> > + */
> > + if (!PXB_DEV(dev)->hdm_for_passthrough) {
>
> However, here we try to cast the device pointer to PXB_DEV.
> That is not permitted because dev is not of type TYPE_PXB_DEVICE
> (either directly or as a parent class). So if you have the QOM
> debugging enabled then the attempt to cast causes an assertion
> failure.
>
> > + dsp_count = pcie_count_ds_ports(hb->bus);
> > + }
> > + /* Initial reset will have 0 dsp so wait until > 0 */
> > + if (dsp_count == 1) {
> > + cxl->passthrough = true;
> > + /* Set Capability ID in header to NONE */
> > + ARRAY_FIELD_DP32(reg_state, CXL_HDM_CAPABILITY_HEADER, ID, 0);
> > + } else {
> > + ARRAY_FIELD_DP32(reg_state, CXL_HDM_DECODER_CAPABILITY,
> > TARGET_COUNT,
> > + 8);
> > + }
> > }
>
> What was the intention here with the type hierarchy?
> Should TYPE_PXB_CXL_DEVICE be a subclass of TYPE_PXB_DEVICE,
> or should the cxl-related functions not be trying to treat
> it as a PXB device ?
I can't immediately recall why, but PXB_DEV and PXB_CXL_DEV use the
same struct PXBDev so here switching to PXB_CXL_DEV(dev)->hdm_for_passthrough
looks to be the minimum fix.
I'll dig into why / if there is a good reason for why PXB_CXL_DEV doesn't
simply inherit from PXB_DEV then use runtime type checking in the few places it
will matter.
Jonathan
>
> thanks
> -- PMM