Re: [RFC PATCH v3 17/31] hw/cxl/component: Implement host bridge MMIO (8.2.5, table 142)

[Jonathan Cameron]

On Mon, 1 Feb 2021 16:59:34 -0800
Ben Widawsky <ben.widawsky@intel.com> wrote:

> CXL host bridges themselves may have MMIO. Since host bridges don't have
> a BAR they are treated as special for MMIO.
> 
> Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
> 
> --
> 
> It's arbitrarily chosen here to pick 0xD0000000 as the base for the host
> bridge MMIO. I'm not sure what the right way to find free space for
> platform hardcoded things like this is.

Seems like this needs to come from the machine definition.
This is fairly easy for arm/virt, where there is a clearly laid out memory map.
For hw/i386 I'm less sure on how to do it.

Having said that, for this particular magic device, we do have a PCI EP
associated with it.  How about putting all the host bridge MMIO into a
BAR of that rather than having it separate.   
That has the added advantage of making it discoverable from firmware.

Any normal system is going to have this is impdef for discovery anyway.

That would then let you drop the separate definition of CXLHost structure
though it needs a bit of figuring out what to do with the memory window
setup etc.

I tried hacking it together, but not gotten it working yet.

> ---
>  hw/pci-bridge/pci_expander_bridge.c | 53 ++++++++++++++++++++++++++++-
>  include/hw/cxl/cxl.h                |  2 ++
>  2 files changed, 54 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/pci-bridge/pci_expander_bridge.c 
> b/hw/pci-bridge/pci_expander_bridge.c
> index 5021b60435..226a8a5fff 100644
> --- a/hw/pci-bridge/pci_expander_bridge.c
> +++ b/hw/pci-bridge/pci_expander_bridge.c
> @@ -17,6 +17,7 @@
>  #include "hw/pci/pci_host.h"
>  #include "hw/qdev-properties.h"
>  #include "hw/pci/pci_bridge.h"
> +#include "hw/cxl/cxl.h"
>  #include "qemu/range.h"
>  #include "qemu/error-report.h"
>  #include "qemu/module.h"
> @@ -70,6 +71,12 @@ struct PXBDev {
>      int32_t uid;
>  };
>  
> +typedef struct CXLHost {
> +    PCIHostState parent_obj;
> +
> +    CXLComponentState cxl_cstate;
> +} CXLHost;
> +
>  static PXBDev *convert_to_pxb(PCIDevice *dev)
>  {
>      /* A CXL PXB's parent bus is PCIe, so the normal check won't work */
> @@ -85,6 +92,9 @@ static GList *pxb_dev_list;
>  
>  #define TYPE_PXB_HOST "pxb-host"
>  
> +#define TYPE_PXB_CXL_HOST "pxb-cxl-host"
> +#define PXB_CXL_HOST(obj) OBJECT_CHECK(CXLHost, (obj), TYPE_PXB_CXL_HOST)
> +
>  static int pxb_bus_num(PCIBus *bus)
>  {
>      PXBDev *pxb = convert_to_pxb(bus->parent_dev);
> @@ -198,6 +208,46 @@ static const TypeInfo pxb_host_info = {
>      .class_init    = pxb_host_class_init,
>  };
>  
> +static void pxb_cxl_realize(DeviceState *dev, Error **errp)
> +{
> +    SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
> +    PCIHostState *phb = PCI_HOST_BRIDGE(dev);
> +    CXLHost *cxl = PXB_CXL_HOST(dev);
> +    CXLComponentState *cxl_cstate = &cxl->cxl_cstate;
> +    struct MemoryRegion *mr = &cxl_cstate->crb.component_registers;
> +
> +    cxl_component_register_block_init(OBJECT(dev), cxl_cstate,
> +                                      TYPE_PXB_CXL_HOST);
> +    sysbus_init_mmio(sbd, mr);
> +
> +    /* FIXME: support multiple host bridges. */
> +    sysbus_mmio_map(sbd, 0, CXL_HOST_BASE +
> +                            memory_region_size(mr) * pci_bus_uid(phb->bus));
> +}
> +
> +static void pxb_cxl_host_class_init(ObjectClass *class, void *data)
> +{
> +    DeviceClass *dc = DEVICE_CLASS(class);
> +    PCIHostBridgeClass *hc = PCI_HOST_BRIDGE_CLASS(class);
> +
> +    hc->root_bus_path = pxb_host_root_bus_path;
> +    dc->fw_name = "cxl";
> +    dc->realize = pxb_cxl_realize;
> +    /* Reason: Internal part of the pxb/pxb-pcie device, not usable by 
> itself */
> +    dc->user_creatable = false;
> +}
> +
> +/*
> + * This is a device to handle the MMIO for a CXL host bridge. It does nothing
> + * else.
> + */
> +static const TypeInfo cxl_host_info = {
> +    .name          = TYPE_PXB_CXL_HOST,
> +    .parent        = TYPE_PCI_HOST_BRIDGE,
> +    .instance_size = sizeof(CXLHost),
> +    .class_init    = pxb_cxl_host_class_init,
> +};
> +
>  /*
>   * Registers the PXB bus as a child of pci host root bus.
>   */
> @@ -272,7 +322,7 @@ static void pxb_dev_realize_common(PCIDevice *dev, enum 
> BusType type,
>          dev_name = dev->qdev.id;
>      }
>  
> -    ds = qdev_new(TYPE_PXB_HOST);
> +    ds = qdev_new(type == CXL ? TYPE_PXB_CXL_HOST : TYPE_PXB_HOST);
>      if (type == PCIE) {
>          bus = pci_root_bus_new(ds, dev_name, NULL, NULL, 0, 
> TYPE_PXB_PCIE_BUS);
>      } else if (type == CXL) {
> @@ -466,6 +516,7 @@ static void pxb_register_types(void)
>      type_register_static(&pxb_pcie_bus_info);
>      type_register_static(&pxb_cxl_bus_info);
>      type_register_static(&pxb_host_info);
> +    type_register_static(&cxl_host_info);
>      type_register_static(&pxb_dev_info);
>      type_register_static(&pxb_pcie_dev_info);
>      type_register_static(&pxb_cxl_dev_info);
> diff --git a/include/hw/cxl/cxl.h b/include/hw/cxl/cxl.h
> index 362cda40de..6bc344f205 100644
> --- a/include/hw/cxl/cxl.h
> +++ b/include/hw/cxl/cxl.h
> @@ -17,5 +17,7 @@
>  #define COMPONENT_REG_BAR_IDX 0
>  #define DEVICE_REG_BAR_IDX 2
>  
> +#define CXL_HOST_BASE 0xD0000000
> +
>  #endif
>