On 21-02-02 10:51:55, Michael S. Tsirkin wrote: > On Tue, Feb 02, 2021 at 07:42:57AM -0800, Ben Widawsky wrote: > > Thanks for looking! Mixing comments to Jonathan and Michael.. > > > > On 21-02-02 10:24:43, Michael S. Tsirkin wrote: > > > On Tue, Feb 02, 2021 at 03:00:56PM +0000, Jonathan Cameron wrote: > > > > On Mon, 1 Feb 2021 16:59:33 -0800 > > > > Ben Widawsky <ben.widaw...@intel.com> wrote: > > > > > > > > > Currently, QEMU makes _UID equivalent to the bus number (_BBN). While > > > > > there is nothing wrong with doing it this way, CXL spec has a heavy > > > > > reliance on _UID to identify host bridges and there is no link to the > > > > > bus number. Having a distinct UID solves two problems. The first is it > > > > > gets us around the limitation of 256 (current max bus number). > > > > > > Not sure I understand. You want more than 256 host bridges? > > > > > > > I don't want more than 256 host bridges, but I want the ability to > > disaggregate > > _UID and bus (_BBN). The reasoning is just to align with the spec where > > _UID is > > used to identify a CXL host bridge which is unrelated (perhaps) to the bus > > number. > > Which spec is that? >
CXL spec https://www.computeexpresslink.org/download-the-specification The spec introduces a new ACPI table which links information about a host bridge based on the _UID. The _UID is 4 bytes. "In an ACPI compliant system, there shall be one instance of CXL Host Bridge Device object in ACPI namespace (HID=”ACPI0016”) for every CHBS entry. The _UID object under a CXL Host Bridge object, when evaluated, shall match the UID field in the associated CHBS entry." "CXL Host Bridge Unique ID. Used to associate a CHBS instance with CXL Host Bridge instance. The value of this field shall match the output of _UID under the associated CXL Host Bridge in ACPI namespace" > > > > The > > > > > second is it allows us to replicate hardware configurations where bus > > > > > number and uid aren't equivalent. > > > > > > A bit more data on when this needs to be the case? > > > > > > > Doesn't *need* to be the case. I was making a concerted effort to allow full > > spec flexibility, but I don't believe it to be necessary unless we want to > > accurately emulate a real platform. > > > > > > The latter has benefits for our > > > > > development and debugging using QEMU. > > > > > > > > > > The other way to do this would be to implement the expanded bus > > > > > numbering, but having an explicit uid makes more sense when trying to > > > > > replicate real hardware configurations. > > > > > > > > > > The QEMU commandline to utilize this would be: > > > > > -device pxb-cxl,id=cxl.0,bus="pcie.0",bus_nr=1,uid=x > > > > > > > > > > Signed-off-by: Ben Widawsky <ben.widaw...@intel.com> > > > > > > However, if doing this how do we ensure UID is still unique? > > > What do we do for cases where UID was not specified? > > > One idea is to generate a string UID and just stick the bus # > > > in there. > > > > This is totally mishandled in the code currently. I like your idea though. > > > > > > > > > > > > > -- > > > > > > > > > > I'm guessing this patch will be somewhat controversial. For early CXL > > > > > work, this can be dropped without too much heartache. > > > > > > > > Whilst I'm not personally against, this maybe best to drop for now as > > > > you > > > > say. > > > > > > > > I think it'd be good to understand from the PCIe experts if CXL matches in > > this > > regard. If PCIe generally allows (and does in practice) _UID not matching > > _BBN, > > perhaps this is an overall improvement to the code. > > Well > > 6.1.12 _UID (Unique ID) > This object provides OSPM with a logical device ID that does not change > across reboots. This object > is optional, but is required when the device has no other way to report > a persistent unique device ID. > The _UID must be unique across all devices with either a common _HID or > _CID. This is because a > device needs to be uniquely identified to the OSPM, which may match on > either a _HID or a _CID to > identify the device. The uniqueness match must be true regardless of > whether the OSPM uses the > _HID or the _CID. OSPM typically uses the unique device ID to ensure > that the device-specific > information, such as network protocol binding information, is > remembered for the device even if its > relative location changes. For most integrated devices, this object > contains a unique identifier. > A _UID object evaluates to either a numeric value or a string. > > > IOW _UID is there so guest can tell devices with identical HID/CID apart. > Right, so it's pretty much the same thing. There's ancillary data about the CXL host bridge that is identified by the _UID. > > > > > > > > --- > > > > > hw/i386/acpi-build.c | 3 ++- > > > > > hw/pci-bridge/pci_expander_bridge.c | 19 +++++++++++++++++++ > > > > > hw/pci/pci.c | 11 +++++++++++ > > > > > include/hw/pci/pci.h | 1 + > > > > > include/hw/pci/pci_bus.h | 1 + > > > > > 5 files changed, 34 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c > > > > > index cf6eb54c22..145a503e92 100644 > > > > > --- a/hw/i386/acpi-build.c > > > > > +++ b/hw/i386/acpi-build.c > > > > > @@ -1343,6 +1343,7 @@ build_dsdt(GArray *table_data, BIOSLinker > > > > > *linker, > > > > > QLIST_FOREACH(bus, &bus->child, sibling) { > > > > > uint8_t bus_num = pci_bus_num(bus); > > > > > uint8_t numa_node = pci_bus_numa_node(bus); > > > > > + int32_t uid = pci_bus_uid(bus); > > > > > > > > > > /* look only for expander root buses */ > > > > > if (!pci_bus_is_root(bus)) { > > > > > @@ -1356,7 +1357,7 @@ build_dsdt(GArray *table_data, BIOSLinker > > > > > *linker, > > > > > scope = aml_scope("\\_SB"); > > > > > dev = aml_device("PC%.02X", bus_num); > > > > > aml_append(dev, aml_name_decl("_BBN", aml_int(bus_num))); > > > > > - init_pci_acpi(dev, bus_num, pci_bus_is_express(bus) ? > > > > > PCIE : PCI); > > > > > + init_pci_acpi(dev, uid, pci_bus_is_express(bus) ? PCIE : > > > > > PCI); > > > > > > > > > > if (numa_node != NUMA_NODE_UNASSIGNED) { > > > > > aml_append(dev, aml_name_decl("_PXM", > > > > > aml_int(numa_node))); > > > > > diff --git a/hw/pci-bridge/pci_expander_bridge.c > > > > > b/hw/pci-bridge/pci_expander_bridge.c > > > > > index b42592e1ff..5021b60435 100644 > > > > > --- a/hw/pci-bridge/pci_expander_bridge.c > > > > > +++ b/hw/pci-bridge/pci_expander_bridge.c > > > > > @@ -67,6 +67,7 @@ struct PXBDev { > > > > > > > > > > uint8_t bus_nr; > > > > > uint16_t numa_node; > > > > > + int32_t uid; > > > > > }; > > > > > > > > > > static PXBDev *convert_to_pxb(PCIDevice *dev) > > > > > > As long as we are doing this, do we want to support a string uid too? > > > How about a 64 bit uid? Why not? > > > > If generally the idea of the patch is welcome, I am happy to change it. > > I am still not sure, let's figure out the motivation. > > For example, grep for UID and you will find more cases > like this. E.g. hw/pci-host/gpex-acpi.c > > Do we care? For my purposes, I do not. > > > > > > > > > > > > > > @@ -98,12 +99,20 @@ static uint16_t pxb_bus_numa_node(PCIBus *bus) > > > > > return pxb->numa_node; > > > > > } > > > > > > > > > > +static int32_t pxb_bus_uid(PCIBus *bus) > > > > > +{ > > > > > + PXBDev *pxb = convert_to_pxb(bus->parent_dev); > > > > > + > > > > > + return pxb->uid; > > > > > +} > > > > > + > > > > > static void pxb_bus_class_init(ObjectClass *class, void *data) > > > > > { > > > > > PCIBusClass *pbc = PCI_BUS_CLASS(class); > > > > > > > > > > pbc->bus_num = pxb_bus_num; > > > > > pbc->numa_node = pxb_bus_numa_node; > > > > > + pbc->uid = pxb_bus_uid; > > > > > } > > > > > > > > > > static const TypeInfo pxb_bus_info = { > > > > > @@ -329,6 +338,7 @@ static Property pxb_dev_properties[] = { > > > > > /* Note: 0 is not a legal PXB bus number. */ > > > > > DEFINE_PROP_UINT8("bus_nr", PXBDev, bus_nr, 0), > > > > > DEFINE_PROP_UINT16("numa_node", PXBDev, numa_node, > > > > > NUMA_NODE_UNASSIGNED), > > > > > + DEFINE_PROP_INT32("uid", PXBDev, uid, -1), > > > > > DEFINE_PROP_END_OF_LIST(), > > > > > }; > > > > > > > > > > @@ -400,12 +410,21 @@ static const TypeInfo pxb_pcie_dev_info = { > > > > > > > > > > static void pxb_cxl_dev_realize(PCIDevice *dev, Error **errp) > > > > > { > > > > > + PXBDev *pxb = convert_to_pxb(dev); > > > > > + > > > > > /* A CXL PXB's parent bus is still PCIe */ > > > > > if (!pci_bus_is_express(pci_get_bus(dev))) { > > > > > error_setg(errp, "pxb-cxl devices cannot reside on a PCI > > > > > bus"); > > > > > return; > > > > > } > > > > > > > > > > + if (pxb->uid < 0) { > > > > > + error_setg(errp, "pxb-cxl devices must have a valid uid > > > > > (0-2147483647)"); > > > > > + return; > > > > > + } > > > > > + > > > > > + /* FIXME: Check that uid doesn't collide with UIDs of other host > > > > > bridges */ > > > > > + > > > > > pxb_dev_realize_common(dev, CXL, errp); > > > > > } > > > > > > > > > > diff --git a/hw/pci/pci.c b/hw/pci/pci.c > > > > > index adbe8aa260..bf019d91a0 100644 > > > > > --- a/hw/pci/pci.c > > > > > +++ b/hw/pci/pci.c > > > > > @@ -170,6 +170,11 @@ static uint16_t pcibus_numa_node(PCIBus *bus) > > > > > return NUMA_NODE_UNASSIGNED; > > > > > } > > > > > > > > > > +static int32_t pcibus_uid(PCIBus *bus) > > > > > +{ > > > > > + return -1; > > > > > +} > > > > > + > > > > > static void pci_bus_class_init(ObjectClass *klass, void *data) > > > > > { > > > > > BusClass *k = BUS_CLASS(klass); > > > > > @@ -184,6 +189,7 @@ static void pci_bus_class_init(ObjectClass > > > > > *klass, void *data) > > > > > > > > > > pbc->bus_num = pcibus_num; > > > > > pbc->numa_node = pcibus_numa_node; > > > > > + pbc->uid = pcibus_uid; > > > > > } > > > > > > > > > > static const TypeInfo pci_bus_info = { > > > > > @@ -530,6 +536,11 @@ int pci_bus_numa_node(PCIBus *bus) > > > > > return PCI_BUS_GET_CLASS(bus)->numa_node(bus); > > > > > } > > > > > > > > > > +int pci_bus_uid(PCIBus *bus) > > > > > +{ > > > > > + return PCI_BUS_GET_CLASS(bus)->uid(bus); > > > > > +} > > > > > + > > > > > static int get_pci_config_device(QEMUFile *f, void *pv, size_t size, > > > > > const VMStateField *field) > > > > > { > > > > > diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h > > > > > index bde3697bee..a46de48ccd 100644 > > > > > --- a/include/hw/pci/pci.h > > > > > +++ b/include/hw/pci/pci.h > > > > > @@ -463,6 +463,7 @@ static inline int pci_dev_bus_num(const PCIDevice > > > > > *dev) > > > > > } > > > > > > > > > > int pci_bus_numa_node(PCIBus *bus); > > > > > +int pci_bus_uid(PCIBus *bus); > > > > > void pci_for_each_device(PCIBus *bus, int bus_num, > > > > > void (*fn)(PCIBus *bus, PCIDevice *d, void > > > > > *opaque), > > > > > void *opaque); > > > > > diff --git a/include/hw/pci/pci_bus.h b/include/hw/pci/pci_bus.h > > > > > index eb94e7e85c..3c9fbc55bb 100644 > > > > > --- a/include/hw/pci/pci_bus.h > > > > > +++ b/include/hw/pci/pci_bus.h > > > > > @@ -17,6 +17,7 @@ struct PCIBusClass { > > > > > > > > > > int (*bus_num)(PCIBus *bus); > > > > > uint16_t (*numa_node)(PCIBus *bus); > > > > > + int32_t (*uid)(PCIBus *bus); > > > > > }; > > > > > > > > > > enum PCIBusFlags { > > > >