[RFC PATCH 16/25] hw/pxb/cxl: Add "windows" for host bridges

[Ben Widawsky]

In a bare metal CXL capable system, system firmware will program
physical address ranges on the host. This is done by programming
internal registers that aren't typically known to OS. These address
ranges might be contiguous or interleaved across host bridges.

For a QEMU guest a new construct is introduced allowing passing a memory
backend to the host bridge for this same purpose. Each memory backend
needs to be passed to the host bridge as well as any device that will be
emulating that memory (not implemented here).

I'm hopeful the interleaving work in the link can be re-purposed here
(see Link).

An example to create a host bridges with a 512M window at 0x4c0000000
 -object memory-backend-file,id=cxl-mem1,share,mem-path=cxl-type3,size=512M
 -device 
pxb-cxl,id=cxl.0,bus=pcie.0,bus_nr=52,uid=0,len-memory-base=1,memory-base\[0\]=0x4c0000000,memory\[0\]=cxl-mem1

Link: https://lists.nongnu.org/archive/html/qemu-devel/2020-08/msg03680.html
Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
---
 hw/pci-bridge/pci_expander_bridge.c | 65 +++++++++++++++++++++++++++--
 include/hw/cxl/cxl.h                |  1 +
 2 files changed, 62 insertions(+), 4 deletions(-)

diff --git a/hw/pci-bridge/pci_expander_bridge.c 
b/hw/pci-bridge/pci_expander_bridge.c
index eca5c71d45..75910f5870 100644
--- a/hw/pci-bridge/pci_expander_bridge.c
+++ b/hw/pci-bridge/pci_expander_bridge.c
@@ -69,12 +69,19 @@ struct PXBDev {
     uint8_t bus_nr;
     uint16_t numa_node;
     int32_t uid;
+    struct cxl_dev {
+        HostMemoryBackend *memory_window[CXL_WINDOW_MAX];
+
+        uint32_t num_windows;
+        hwaddr *window_base[CXL_WINDOW_MAX];
+    } cxl;
 };
 
 typedef struct CXLHost {
     PCIHostState parent_obj;
 
     CXLComponentState cxl_cstate;
+    PXBDev *dev;
 } CXLHost;
 
 static PXBDev *convert_to_pxb(PCIDevice *dev)
@@ -213,16 +220,31 @@ 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);
+    struct cxl_dev *cxl_dev = &cxl->dev->cxl;
     CXLComponentState *cxl_cstate = &cxl->cxl_cstate;
     struct MemoryRegion *mr = &cxl_cstate->crb.component_registers;
+    int uid = pci_bus_uid(phb->bus);
 
     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));
+    sysbus_mmio_map(sbd, 0, CXL_HOST_BASE + memory_region_size(mr) * uid);
+
+    /*
+     * A CXL host bridge can exist without a fixed memory window, but it would
+     * only operate in legacy PCIe mode.
+     */
+    if (!cxl_dev->memory_window[uid]) {
+        warn_report(
+            "CXL expander bridge created without window. Consider using %s",
+            "memdev[0]=<memory_backend>");
+        return;
+    }
+
+    mr = host_memory_backend_get_memory(cxl_dev->memory_window[uid]);
+    sysbus_init_mmio(sbd, mr);
+    sysbus_mmio_map(sbd, 1 + uid, *cxl_dev->window_base[uid]);
 }
 
 static void pxb_cxl_host_class_init(ObjectClass *class, void *data)
@@ -328,6 +350,7 @@ static void pxb_dev_realize_common(PCIDevice *dev, enum 
BusType type,
     } else if (type == CXL) {
         bus = pci_root_bus_new(ds, dev_name, NULL, NULL, 0, TYPE_PXB_CXL_BUS);
         bus->flags |= PCI_BUS_CXL;
+        PXB_CXL_HOST(ds)->dev = PXB_CXL_DEV(dev);
     } else {
         bus = pci_root_bus_new(ds, "pxb-internal", NULL, NULL, 0, 
TYPE_PXB_BUS);
         bds = qdev_new("pci-bridge");
@@ -389,6 +412,8 @@ static Property pxb_dev_properties[] = {
     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_ARRAY("window-base", PXBDev, cxl.num_windows, cxl.window_base,
+                      qdev_prop_uint64, hwaddr),
     DEFINE_PROP_END_OF_LIST(),
 };
 
@@ -460,7 +485,9 @@ static const TypeInfo pxb_pcie_dev_info = {
 
 static void pxb_cxl_dev_realize(PCIDevice *dev, Error **errp)
 {
-    PXBDev *pxb = convert_to_pxb(dev);
+    PXBDev *pxb = PXB_CXL_DEV(dev);
+    struct cxl_dev *cxl = &pxb->cxl;
+    int count = 0;
 
     /* A CXL PXB's parent bus is still PCIe */
     if (!pci_bus_is_express(pci_get_bus(dev))) {
@@ -476,6 +503,23 @@ static void pxb_cxl_dev_realize(PCIDevice *dev, Error 
**errp)
     /* FIXME: Check that uid doesn't collide with UIDs of other host bridges */
 
     pxb_dev_realize_common(dev, CXL, errp);
+
+    for (unsigned i = 0; i < CXL_WINDOW_MAX; i++) {
+        if (!cxl->memory_window[i]) {
+            continue;
+        }
+
+        count++;
+    }
+
+    if (!count) {
+        warn_report("memory-windows should be set when creating CXL host 
bridges");
+    }
+
+    if (count != cxl->num_windows) {
+        error_setg(errp, "window bases count (%d) must match window count 
(%d)",
+                   cxl->num_windows, count);
+    }
 }
 
 static void pxb_cxl_dev_class_init(ObjectClass *klass, void *data)
@@ -496,6 +540,19 @@ static void pxb_cxl_dev_class_init(ObjectClass *klass, 
void *data)
 
     /* Host bridges aren't hotpluggable. FIXME: spec reference */
     dc->hotpluggable = false;
+
+    /*
+     * Below is moral equivalent of:
+     *   DEFINE_PROP_ARRAY("memdev", PXBDev, window_count, windows,
+     *                     qdev_prop_memory_device, HostMemoryBackend)
+     */
+    for (unsigned i = 0; i < CXL_WINDOW_MAX; i++) {
+        g_autofree char *name = g_strdup_printf("memdev[%u]", i);
+        object_class_property_add_link(klass, name, TYPE_MEMORY_BACKEND,
+                offsetof(PXBDev, cxl.memory_window[i]),
+                qdev_prop_allow_set_link_before_realize,
+                OBJ_PROP_LINK_STRONG);
+    }
 }
 
 static const TypeInfo pxb_cxl_dev_info = {
diff --git a/include/hw/cxl/cxl.h b/include/hw/cxl/cxl.h
index 6bc344f205..b1e5f4a8fa 100644
--- a/include/hw/cxl/cxl.h
+++ b/include/hw/cxl/cxl.h
@@ -18,6 +18,7 @@
 #define DEVICE_REG_BAR_IDX 2
 
 #define CXL_HOST_BASE 0xD0000000
+#define CXL_WINDOW_MAX 10
 
 #endif
 
-- 
2.29.2