[RFC PATCH v3 0/2] cxl: Support creation of a new CXL Host Bridge

[RFC PATCH v3 0/2] cxl: Support creation of a new CXL Host Bridge

[wangyuquan]

v2 -> v3:
- Update the commit message
- Fix some alignment and space problems
- Add a SPDX header for the new file
- Remove unnecessary comments
- Add CXL_HOST_BRIDGE config
v1 -> v2:
- Move the code of new bridge to hw/pci-host/cxl.c
- Fix and simplify some logic on handling the different bridge types

Background
==========
Currently the base CXL support for arm platforms is only on Jonathan's
patches[1]. Some platform like SBSA-REF can be more like a real machine,
thus the support of CXL could be meaningful. However, the pxb-cxl-host
realization on this platform seems not satisfying their requirements[2].

New CXL HOST design
===================
Defines a new CXL host bridge type (TYPE_CXL_HOST). This is an
independent CXL host bridge which combined GPEX features (ECAM, MMIO
windows and irq) and CXL Host Bridge Component Registers (CHBCR).

The root bus path of CXL_HOST is "0001:00", that would not affect the
original pcie host topology. In the previous, the pxb-cxl-host with
any CXL root ports and CXL endpoint devices would occupy the BDF
number of the original pcie domain. This new type provide a solution
to resolve the problem.

Remaining problems
==================
I tried to use 'object_resolve_path' but it could not work in
'cxl_fmws_link_targets', so I used 'TYPE_DEVICE' to match that.

Link:
[1]: https://lore.kernel.org/linux-cxl/20220616141950.23374-1-Jonathan.Cameron@huawei.com/
[2]: https://lists.nongnu.org/archive/html/qemu-arm/2024-11/msg00522.html

Yuquan Wang (2):
  pci-host/cxl: Support creation of a new CXL Host Bridge
  hw/pxb-cxl: Rename the pxb cxl host bridge

 hw/cxl/cxl-host-stubs.c               |   3 +
 hw/cxl/cxl-host.c                     |  64 ++++++++---
 hw/pci-bridge/pci_expander_bridge.c   |   8 +-
 hw/pci-host/Kconfig                   |   4 +
 hw/pci-host/cxl.c                     | 152 ++++++++++++++++++++++++++
 hw/pci-host/meson.build               |   1 +
 include/hw/cxl/cxl.h                  |   7 +-
 include/hw/cxl/cxl_host.h             |   3 +
 include/hw/pci-host/cxl_host_bridge.h |  23 ++++
 9 files changed, 244 insertions(+), 21 deletions(-)
 create mode 100644 hw/pci-host/cxl.c
 create mode 100644 include/hw/pci-host/cxl_host_bridge.h

-- 
2.34.1

[RFC PATCH v3 1/2] hw/pxb-cxl: Rename the pxb cxl host bridge

[wangyuquan]

This renames some descriptions and definitions of pxb cxl host
bridge, since the original names can be confusing.

Signed-off-by: Yuquan Wang <wangyuquan1236@phytium.com.cn>
---
 hw/pci-bridge/pci_expander_bridge.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/hw/pci-bridge/pci_expander_bridge.c b/hw/pci-bridge/pci_expander_bridge.c
index 3a29dfefc2..bd637786d0 100644
--- a/hw/pci-bridge/pci_expander_bridge.c
+++ b/hw/pci-bridge/pci_expander_bridge.c
@@ -201,7 +201,7 @@ static void pxb_cxl_realize(DeviceState *dev, Error **errp)
 }
 
 /*
- * Host bridge realization has no means of knowning state associated
+ * PXB Host bridge realization has no means of knowning state associated
  * with a particular machine. As such, it is nececssary to delay
  * final setup of the host bridge register space until later in the
  * machine bring up.
@@ -240,7 +240,7 @@ static void pxb_cxl_host_class_init(ObjectClass *class, const void *data)
  * This is a device to handle the MMIO for a CXL host bridge. It does nothing
  * else.
  */
-static const TypeInfo cxl_host_info = {
+static const TypeInfo pxb_cxl_host_info = {
     .name          = TYPE_PXB_CXL_HOST,
     .parent        = TYPE_PCI_HOST_BRIDGE,
     .instance_size = sizeof(CXLHost),
@@ -522,7 +522,7 @@ static void pxb_cxl_dev_class_init(ObjectClass *klass, const void *data)
      * vendor, device, class, etc. ids are intentionally left out.
      */
 
-    dc->desc = "CXL Host Bridge";
+    dc->desc = "PXB CXL Host Bridge";
     device_class_set_props(dc, pxb_cxl_dev_properties);
     set_bit(DEVICE_CATEGORY_BRIDGE, dc->categories);
 
@@ -549,7 +549,7 @@ 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_cxl_host_info);
     type_register_static(&pxb_dev_info);
     type_register_static(&pxb_pcie_dev_info);
     type_register_static(&pxb_cxl_dev_info);
-- 
2.34.1

[RFC PATCH v3 2/2] pci-host/cxl: Support creation of a new CXL Host Bridge

[wangyuquan]

From: Yuquan Wang <wangyuquan1236@phytium.com.cn>

Define a new CXL host bridge type (TYPE_CXL_HOST). This is an
independent CXL host bridge which combined GPEX features (ECAM, MMIO
windows and irq) and CXL Host Bridge Component Registers (CHBCR).

The root bus path of CXL_HOST is "0001:00", that would not affect the
original PCIe host topology on some platforms. In the previous, the
pxb-cxl-host with any CXL root ports and CXL endpoint devices would
share the resources (like BDF, MMIO space) of the original pcie
domain, but it would cause some platforms like sbsa-ref are unable to
support the original number of PCIe devices. The new type provides a
solution to resolve the problem.

Signed-off-by: Yuquan Wang <wangyuquan1236@phytium.com.cn>
---
 hw/cxl/cxl-host-stubs.c               |   3 +
 hw/cxl/cxl-host.c                     |  64 ++++++++---
 hw/pci-host/Kconfig                   |   4 +
 hw/pci-host/cxl.c                     | 152 ++++++++++++++++++++++++++
 hw/pci-host/meson.build               |   1 +
 include/hw/cxl/cxl.h                  |   7 +-
 include/hw/cxl/cxl_host.h             |   3 +
 include/hw/pci-host/cxl_host_bridge.h |  23 ++++
 8 files changed, 240 insertions(+), 17 deletions(-)
 create mode 100644 hw/pci-host/cxl.c
 create mode 100644 include/hw/pci-host/cxl_host_bridge.h

diff --git a/hw/cxl/cxl-host-stubs.c b/hw/cxl/cxl-host-stubs.c
index cae4afcdde..2131331af1 100644
--- a/hw/cxl/cxl-host-stubs.c
+++ b/hw/cxl/cxl-host-stubs.c
@@ -11,5 +11,8 @@
 void cxl_fmws_link_targets(CXLState *stat, Error **errp) {};
 void cxl_machine_init(Object *obj, CXLState *state) {};
 void cxl_hook_up_pxb_registers(PCIBus *bus, CXLState *state, Error **errp) {};
+void cxl_fixed_memory_window_config(CXLState *cxl_state,
+                                    CXLFixedMemoryWindowOptions *object,
+                                    Error **errp) {};
 
 const MemoryRegionOps cfmws_ops;
diff --git a/hw/cxl/cxl-host.c b/hw/cxl/cxl-host.c
index e010163174..fe7545abc1 100644
--- a/hw/cxl/cxl-host.c
+++ b/hw/cxl/cxl-host.c
@@ -16,15 +16,17 @@
 #include "qapi/qapi-visit-machine.h"
 #include "hw/cxl/cxl.h"
 #include "hw/cxl/cxl_host.h"
+#include "hw/irq.h"
 #include "hw/pci/pci_bus.h"
 #include "hw/pci/pci_bridge.h"
 #include "hw/pci/pci_host.h"
 #include "hw/pci/pcie_port.h"
 #include "hw/pci-bridge/pci_expander_bridge.h"
+#include "hw/pci-host/cxl_host_bridge.h"
 
-static void cxl_fixed_memory_window_config(CXLState *cxl_state,
-                                           CXLFixedMemoryWindowOptions *object,
-                                           Error **errp)
+void cxl_fixed_memory_window_config(CXLState *cxl_state,
+                                    CXLFixedMemoryWindowOptions *object,
+                                    Error **errp)
 {
     ERRP_GUARD();
     g_autofree CXLFixedWindow *fw = g_malloc0(sizeof(*fw));
@@ -83,14 +85,16 @@ void cxl_fmws_link_targets(CXLState *cxl_state, Error **errp)
                 bool ambig;
 
                 o = object_resolve_path_type(fw->targets[i],
-                                             TYPE_PXB_CXL_DEV,
-                                             &ambig);
-                if (!o) {
+                                             TYPE_DEVICE, &ambig);
+
+                if (object_dynamic_cast(o, TYPE_PXB_CXL_DEV) ||
+                    object_dynamic_cast(o, TYPE_CXL_HOST)) {
+                    fw->target_hbs[i] = o;
+                } else {
                     error_setg(errp, "Could not resolve CXLFM target %s",
                                fw->targets[i]);
                     return;
                 }
-                fw->target_hbs[i] = PXB_CXL_DEV(o);
             }
         }
     }
@@ -153,6 +157,7 @@ static bool cxl_hdm_find_target(uint32_t *cache_mem, hwaddr addr,
 static PCIDevice *cxl_cfmws_find_device(CXLFixedWindow *fw, hwaddr addr)
 {
     CXLComponentState *hb_cstate, *usp_cstate;
+    CXLHostBridge *cxlhost;
     PCIHostState *hb;
     CXLUpstreamPort *usp;
     int rb_index;
@@ -160,23 +165,50 @@ static PCIDevice *cxl_cfmws_find_device(CXLFixedWindow *fw, hwaddr addr)
     uint8_t target;
     bool target_found;
     PCIDevice *rp, *d;
+    Object *o;
 
     /* Address is relative to memory region. Convert to HPA */
     addr += fw->base;
 
     rb_index = (addr / cxl_decode_ig(fw->enc_int_gran)) % fw->num_targets;
-    hb = PCI_HOST_BRIDGE(fw->target_hbs[rb_index]->cxl_host_bridge);
-    if (!hb || !hb->bus || !pci_bus_is_cxl(hb->bus)) {
-        return NULL;
-    }
-
-    if (cxl_get_hb_passthrough(hb)) {
-        rp = pcie_find_port_first(hb->bus);
-        if (!rp) {
+    o = fw->target_hbs[rb_index];
+    if (object_dynamic_cast(o, TYPE_PXB_CXL_DEV)) {
+        hb = PCI_HOST_BRIDGE(PXB_CXL_DEV(o)->cxl_host_bridge);
+        if (!hb || !hb->bus || !pci_bus_is_cxl(hb->bus)) {
             return NULL;
         }
+
+        if (cxl_get_hb_passthrough(hb)) {
+            rp = pcie_find_port_first(hb->bus);
+            if (!rp) {
+                return NULL;
+            }
+        } else {
+            hb_cstate = cxl_get_hb_cstate(hb);
+            if (!hb_cstate) {
+                return NULL;
+            }
+
+            cache_mem = hb_cstate->crb.cache_mem_registers;
+
+            target_found = cxl_hdm_find_target(cache_mem, addr, &target);
+            if (!target_found) {
+                return NULL;
+            }
+
+            rp = pcie_find_port_by_pn(hb->bus, target);
+            if (!rp) {
+                return NULL;
+            }
+        }
     } else {
-        hb_cstate = cxl_get_hb_cstate(hb);
+        hb = PCI_HOST_BRIDGE(o);
+        if (!hb || !hb->bus || !pci_bus_is_cxl(hb->bus)) {
+            return NULL;
+        }
+
+        cxlhost = CXL_HOST(hb);
+        hb_cstate = &cxlhost->cxl_cstate;
         if (!hb_cstate) {
             return NULL;
         }
diff --git a/hw/pci-host/Kconfig b/hw/pci-host/Kconfig
index 35c0415242..05c772bcf4 100644
--- a/hw/pci-host/Kconfig
+++ b/hw/pci-host/Kconfig
@@ -74,6 +74,10 @@ config PCI_POWERNV
     select MSI_NONBROKEN
     select PCIE_PORT
 
+config CXL_HOST_BRIDGE
+    bool
+    select PCI_EXPRESS
+
 config REMOTE_PCIHOST
     bool
 
diff --git a/hw/pci-host/cxl.c b/hw/pci-host/cxl.c
new file mode 100644
index 0000000000..74c8c83314
--- /dev/null
+++ b/hw/pci-host/cxl.c
@@ -0,0 +1,152 @@
+/*
+ * QEMU CXL Host Bridge Emulation
+ *
+ * Copyright (C) 2025, Phytium Technology Co, Ltd. All rights reserved.
+ *
+ * Based on gpex.c
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "hw/pci/pci_bus.h"
+#include "hw/pci-host/cxl_host_bridge.h"
+
+static void cxl_host_set_irq(void *opaque, int irq_num, int level)
+{
+    CXLHostBridge *host = opaque;
+
+    qemu_set_irq(host->irq[irq_num], level);
+}
+
+int cxl_host_set_irq_num(CXLHostBridge *host, int index, int gsi)
+{
+    if (index >= PCI_NUM_PINS) {
+        return -EINVAL;
+    }
+
+    host->irq_num[index] = gsi;
+    return 0;
+}
+
+static PCIINTxRoute cxl_host_route_intx_pin_to_irq(void *opaque, int pin)
+{
+    PCIINTxRoute route;
+    CXLHostBridge *host = opaque;
+    int gsi = host->irq_num[pin];
+
+    route.irq = gsi;
+    if (gsi < 0) {
+        route.mode = PCI_INTX_DISABLED;
+    } else {
+        route.mode = PCI_INTX_ENABLED;
+    }
+
+    return route;
+}
+
+static const char *cxl_host_root_bus_path(PCIHostState *host_bridge,
+                                          PCIBus *rootbus)
+{
+    return "0001:00";
+}
+
+void cxl_host_hook_up_registers(CXLState *cxl_state, CXLHostBridge *host)
+{
+    CXLComponentState *cxl_cstate = &host->cxl_cstate;
+    struct MemoryRegion *mr = &cxl_cstate->crb.component_registers;
+
+    memory_region_add_subregion(&cxl_state->host_mr, 0, mr);
+}
+
+static void cxl_host_reset(CXLHostBridge *host)
+{
+    CXLComponentState *cxl_cstate = &host->cxl_cstate;
+    uint32_t *reg_state = cxl_cstate->crb.cache_mem_registers;
+    uint32_t *write_msk = cxl_cstate->crb.cache_mem_regs_write_mask;
+
+    cxl_component_register_init_common(reg_state, write_msk, CXL2_RC);
+
+    ARRAY_FIELD_DP32(reg_state, CXL_HDM_DECODER_CAPABILITY, TARGET_COUNT,
+                     8);
+}
+
+static void cxl_host_realize(DeviceState *dev, Error **errp)
+{
+    SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
+    CXLHostBridge *host = CXL_HOST(dev);
+    CXLComponentState *cxl_cstate = &host->cxl_cstate;
+    struct MemoryRegion *mr = &cxl_cstate->crb.component_registers;
+    PCIHostState *pci = PCI_HOST_BRIDGE(dev);
+    PCIExpressHost *pex = PCIE_HOST_BRIDGE(dev);
+    PCIBus *cxlbus;
+    int i;
+
+    cxl_host_reset(host);
+    cxl_component_register_block_init(OBJECT(dev), cxl_cstate, TYPE_CXL_HOST);
+    sysbus_init_mmio(sbd, mr);
+
+    pcie_host_mmcfg_init(pex, PCIE_MMCFG_SIZE_MAX);
+    sysbus_init_mmio(sbd, &pex->mmio);
+
+    memory_region_init(&host->io_mmio, OBJECT(host), "cxl_host_mmio",
+                        UINT64_MAX);
+
+    memory_region_init_io(&host->io_mmio_window, OBJECT(host),
+                              &unassigned_io_ops, OBJECT(host),
+                              "cxl_host_mmio_window", UINT64_MAX);
+
+    memory_region_add_subregion(&host->io_mmio_window, 0, &host->io_mmio);
+    sysbus_init_mmio(sbd, &host->io_mmio_window);
+
+    /* ioport window init, 64K is the legacy size in x86 */
+    memory_region_init(&host->io_ioport, OBJECT(host), "cxl_host_ioport",
+                        64 * 1024);
+
+    memory_region_init_io(&host->io_ioport_window, OBJECT(host),
+                              &unassigned_io_ops, OBJECT(host),
+                              "cxl_host_ioport_window", 64 * 1024);
+
+    memory_region_add_subregion(&host->io_ioport_window, 0, &host->io_ioport);
+    sysbus_init_mmio(sbd, &host->io_ioport_window);
+
+    /* PCIe host bridge use 4 legacy IRQ lines */
+    for (i = 0; i < PCI_NUM_PINS; i++) {
+        sysbus_init_irq(sbd, &host->irq[i]);
+        host->irq_num[i] = -1;
+    }
+
+    pci->bus = pci_register_root_bus(dev, "cxlhost.0", cxl_host_set_irq,
+                                 pci_swizzle_map_irq_fn, host, &host->io_mmio,
+                                 &host->io_ioport, 0, 4, TYPE_CXL_BUS);
+    cxlbus = pci->bus;
+    cxlbus->flags |= PCI_BUS_CXL;
+
+    pci_bus_set_route_irq_fn(pci->bus, cxl_host_route_intx_pin_to_irq);
+}
+
+static void cxl_host_class_init(ObjectClass *class, const void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(class);
+    PCIHostBridgeClass *hc = PCI_HOST_BRIDGE_CLASS(class);
+
+    hc->root_bus_path = cxl_host_root_bus_path;
+    dc->realize = cxl_host_realize;
+    dc->desc = "CXL Host Bridge";
+    set_bit(DEVICE_CATEGORY_BRIDGE, dc->categories);
+    dc->fw_name = "cxl";
+}
+
+static const TypeInfo cxl_host_info = {
+    .name          = TYPE_CXL_HOST,
+    .parent        = TYPE_PCIE_HOST_BRIDGE,
+    .instance_size = sizeof(CXLHostBridge),
+    .class_init    = cxl_host_class_init,
+};
+
+static void cxl_host_register(void)
+{
+    type_register_static(&cxl_host_info);
+}
+
+type_init(cxl_host_register)
diff --git a/hw/pci-host/meson.build b/hw/pci-host/meson.build
index 937a0f72ac..030672373d 100644
--- a/hw/pci-host/meson.build
+++ b/hw/pci-host/meson.build
@@ -4,6 +4,7 @@ pci_ss.add(when: 'CONFIG_PCI_BONITO', if_true: files('bonito.c'))
 pci_ss.add(when: 'CONFIG_GT64120', if_true: files('gt64120.c'))
 pci_ss.add(when: 'CONFIG_PCI_EXPRESS_DESIGNWARE', if_true: files('designware.c'))
 pci_ss.add(when: 'CONFIG_PCI_EXPRESS_GENERIC_BRIDGE', if_true: files('gpex.c'))
+pci_ss.add(when: 'CONFIG_CXL_HOST_BRIDGE', if_true: files('cxl.c'))
 pci_ss.add(when: ['CONFIG_PCI_EXPRESS_GENERIC_BRIDGE', 'CONFIG_ACPI'], if_true: files('gpex-acpi.c'))
 pci_ss.add(when: 'CONFIG_PCI_EXPRESS_Q35', if_true: files('q35.c'))
 pci_ss.add(when: 'CONFIG_PCI_EXPRESS_XILINX', if_true: files('xilinx-pcie.c'))
diff --git a/include/hw/cxl/cxl.h b/include/hw/cxl/cxl.h
index 75e47b6864..346a7b58ad 100644
--- a/include/hw/cxl/cxl.h
+++ b/include/hw/cxl/cxl.h
@@ -26,10 +26,12 @@
 
 typedef struct PXBCXLDev PXBCXLDev;
 
+typedef struct CXLHostBridge CXLHostBridge;
+
 typedef struct CXLFixedWindow {
     uint64_t size;
     char **targets;
-    PXBCXLDev *target_hbs[16];
+    Object *target_hbs[16];
     uint8_t num_targets;
     uint8_t enc_int_ways;
     uint8_t enc_int_gran;
@@ -56,6 +58,9 @@ struct CXLHost {
 #define TYPE_PXB_CXL_HOST "pxb-cxl-host"
 OBJECT_DECLARE_SIMPLE_TYPE(CXLHost, PXB_CXL_HOST)
 
+#define TYPE_CXL_HOST "cxl-host"
+OBJECT_DECLARE_SIMPLE_TYPE(CXLHostBridge, CXL_HOST)
+
 #define TYPE_CXL_USP "cxl-upstream"
 
 typedef struct CXLUpstreamPort CXLUpstreamPort;
diff --git a/include/hw/cxl/cxl_host.h b/include/hw/cxl/cxl_host.h
index c9bc9c7c50..6aeb0507de 100644
--- a/include/hw/cxl/cxl_host.h
+++ b/include/hw/cxl/cxl_host.h
@@ -16,6 +16,9 @@
 void cxl_machine_init(Object *obj, CXLState *state);
 void cxl_fmws_link_targets(CXLState *stat, Error **errp);
 void cxl_hook_up_pxb_registers(PCIBus *bus, CXLState *state, Error **errp);
+void cxl_fixed_memory_window_config(CXLState *cxl_state,
+                                    CXLFixedMemoryWindowOptions *object,
+                                    Error **errp);
 
 extern const MemoryRegionOps cfmws_ops;
 
diff --git a/include/hw/pci-host/cxl_host_bridge.h b/include/hw/pci-host/cxl_host_bridge.h
new file mode 100644
index 0000000000..833e460f01
--- /dev/null
+++ b/include/hw/pci-host/cxl_host_bridge.h
@@ -0,0 +1,23 @@
+/*
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "hw/cxl/cxl.h"
+#include "hw/irq.h"
+#include "hw/pci/pcie_host.h"
+
+typedef struct CXLHostBridge {
+    PCIExpressHost parent_obj;
+
+    CXLComponentState cxl_cstate;
+
+    MemoryRegion io_ioport;
+    MemoryRegion io_mmio;
+    MemoryRegion io_ioport_window;
+    MemoryRegion io_mmio_window;
+    qemu_irq irq[PCI_NUM_PINS];
+    int irq_num[PCI_NUM_PINS];
+} CXLHostBridge;
+
+int cxl_host_set_irq_num(CXLHostBridge *host, int index, int gsi);
+void cxl_host_hook_up_registers(CXLState *cxl_state, CXLHostBridge *host);
-- 
2.34.1

Re: [RFC PATCH v3 1/2] hw/pxb-cxl: Rename the pxb cxl host bridge

[Jonathan Cameron via]

On Tue, 17 Jun 2025 12:06:48 +0800
wangyuquan <wangyuquan1236@phytium.com.cn> wrote:

> This renames some descriptions and definitions of pxb cxl host
> bridge, since the original names can be confusing.
> 
> Signed-off-by: Yuquan Wang <wangyuquan1236@phytium.com.cn>
Fair enough.
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>

> ---
>  hw/pci-bridge/pci_expander_bridge.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/pci-bridge/pci_expander_bridge.c b/hw/pci-bridge/pci_expander_bridge.c
> index 3a29dfefc2..bd637786d0 100644
> --- a/hw/pci-bridge/pci_expander_bridge.c
> +++ b/hw/pci-bridge/pci_expander_bridge.c
> @@ -201,7 +201,7 @@ static void pxb_cxl_realize(DeviceState *dev, Error **errp)
>  }
>  
>  /*
> - * Host bridge realization has no means of knowning state associated
> + * PXB Host bridge realization has no means of knowning state associated
>   * with a particular machine. As such, it is nececssary to delay
>   * final setup of the host bridge register space until later in the
>   * machine bring up.
> @@ -240,7 +240,7 @@ static void pxb_cxl_host_class_init(ObjectClass *class, const void *data)
>   * This is a device to handle the MMIO for a CXL host bridge. It does nothing
>   * else.
>   */
> -static const TypeInfo cxl_host_info = {
> +static const TypeInfo pxb_cxl_host_info = {
>      .name          = TYPE_PXB_CXL_HOST,
>      .parent        = TYPE_PCI_HOST_BRIDGE,
>      .instance_size = sizeof(CXLHost),
> @@ -522,7 +522,7 @@ static void pxb_cxl_dev_class_init(ObjectClass *klass, const void *data)
>       * vendor, device, class, etc. ids are intentionally left out.
>       */
>  
> -    dc->desc = "CXL Host Bridge";
> +    dc->desc = "PXB CXL Host Bridge";
>      device_class_set_props(dc, pxb_cxl_dev_properties);
>      set_bit(DEVICE_CATEGORY_BRIDGE, dc->categories);
>  
> @@ -549,7 +549,7 @@ 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_cxl_host_info);
>      type_register_static(&pxb_dev_info);
>      type_register_static(&pxb_pcie_dev_info);
>      type_register_static(&pxb_cxl_dev_info);

Re: [RFC PATCH v3 2/2] pci-host/cxl: Support creation of a new CXL Host Bridge

[Jonathan Cameron via]

On Tue, 17 Jun 2025 12:06:49 +0800
wangyuquan <wangyuquan1236@phytium.com.cn> wrote:

> From: Yuquan Wang <wangyuquan1236@phytium.com.cn>
> 
> Define a new CXL host bridge type (TYPE_CXL_HOST). This is an
> independent CXL host bridge which combined GPEX features (ECAM, MMIO
> windows and irq) and CXL Host Bridge Component Registers (CHBCR).
> 
> The root bus path of CXL_HOST is "0001:00", that would not affect the
> original PCIe host topology on some platforms. In the previous, the
> pxb-cxl-host with any CXL root ports and CXL endpoint devices would
> share the resources (like BDF, MMIO space) of the original pcie
> domain, but it would cause some platforms like sbsa-ref are unable to
> support the original number of PCIe devices. The new type provides a
> solution to resolve the problem.
> 
> Signed-off-by: Yuquan Wang <wangyuquan1236@phytium.com.cn>
A few trivial things inline.  To me this looks fine but it needs more
eyes, particularly form PCI folk on whether anything is missing for the
host bridge.

> diff --git a/hw/pci-host/Kconfig b/hw/pci-host/Kconfig
> index 35c0415242..05c772bcf4 100644
> --- a/hw/pci-host/Kconfig
> +++ b/hw/pci-host/Kconfig
> @@ -74,6 +74,10 @@ config PCI_POWERNV
>      select MSI_NONBROKEN
>      select PCIE_PORT
>  
> +config CXL_HOST_BRIDGE
> +    bool
> +    select PCI_EXPRESS
> +
>  config REMOTE_PCIHOST
>      bool
>  
> diff --git a/hw/pci-host/cxl.c b/hw/pci-host/cxl.c
> new file mode 100644
> index 0000000000..74c8c83314
> --- /dev/null
> +++ b/hw/pci-host/cxl.c
> @@ -0,0 +1,152 @@
> +/*
> + * QEMU CXL Host Bridge Emulation
> + *
> + * Copyright (C) 2025, Phytium Technology Co, Ltd. All rights reserved.
> + *
> + * Based on gpex.c
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#include "qemu/osdep.h"
> +#include "hw/pci/pci_bus.h"
> +#include "hw/pci-host/cxl_host_bridge.h"
> +
> +static void cxl_host_set_irq(void *opaque, int irq_num, int level)
> +{
> +    CXLHostBridge *host = opaque;
> +
> +    qemu_set_irq(host->irq[irq_num], level);
> +}
> +
> +int cxl_host_set_irq_num(CXLHostBridge *host, int index, int gsi)
> +{
> +    if (index >= PCI_NUM_PINS) {
> +        return -EINVAL;
> +    }
> +
> +    host->irq_num[index] = gsi;
> +    return 0;
> +}
> +
> +static PCIINTxRoute cxl_host_route_intx_pin_to_irq(void *opaque, int pin)
> +{
> +    PCIINTxRoute route;
> +    CXLHostBridge *host = opaque;
> +    int gsi = host->irq_num[pin];
> +
> +    route.irq = gsi;
> +    if (gsi < 0) {
> +        route.mode = PCI_INTX_DISABLED;
> +    } else {
> +        route.mode = PCI_INTX_ENABLED;
> +    }
> +
> +    return route;
    CXLHostBridge *host = opaque;
    int gsi = host->irq_num[pin];
    PCIINTxRoute route = {
       .irq = gsi,
       .mode = gsi < 0 ? PCI_INTX_DISABLED : PCI_INTX_ENABLED,
    }

    return route;

perhaps?  Or maybe not worth bothering.

    
> +}

> +static void cxl_host_realize(DeviceState *dev, Error **errp)
> +{
> +    SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
> +    CXLHostBridge *host = CXL_HOST(dev);
> +    CXLComponentState *cxl_cstate = &host->cxl_cstate;
> +    struct MemoryRegion *mr = &cxl_cstate->crb.component_registers;
> +    PCIHostState *pci = PCI_HOST_BRIDGE(dev);
> +    PCIExpressHost *pex = PCIE_HOST_BRIDGE(dev);
> +    PCIBus *cxlbus;
> +    int i;
> +
> +    cxl_host_reset(host);
> +    cxl_component_register_block_init(OBJECT(dev), cxl_cstate, TYPE_CXL_HOST);
> +    sysbus_init_mmio(sbd, mr);
> +
> +    pcie_host_mmcfg_init(pex, PCIE_MMCFG_SIZE_MAX);
> +    sysbus_init_mmio(sbd, &pex->mmio);
> +
> +    memory_region_init(&host->io_mmio, OBJECT(host), "cxl_host_mmio",
> +                        UINT64_MAX);
> +
> +    memory_region_init_io(&host->io_mmio_window, OBJECT(host),
> +                              &unassigned_io_ops, OBJECT(host),

Odd code alignment.  The & should be under the &
Check for other instances of this.

> +                              "cxl_host_mmio_window", UINT64_MAX);
> +
> +    memory_region_add_subregion(&host->io_mmio_window, 0, &host->io_mmio);
> +    sysbus_init_mmio(sbd, &host->io_mmio_window);
> +
> +    /* ioport window init, 64K is the legacy size in x86 */
> +    memory_region_init(&host->io_ioport, OBJECT(host), "cxl_host_ioport",
> +                        64 * 1024);
> +
> +    memory_region_init_io(&host->io_ioport_window, OBJECT(host),
> +                              &unassigned_io_ops, OBJECT(host),
> +                              "cxl_host_ioport_window", 64 * 1024);
> +
> +    memory_region_add_subregion(&host->io_ioport_window, 0, &host->io_ioport);
> +    sysbus_init_mmio(sbd, &host->io_ioport_window);
> +
> +    /* PCIe host bridge use 4 legacy IRQ lines */
> +    for (i = 0; i < PCI_NUM_PINS; i++) {
> +        sysbus_init_irq(sbd, &host->irq[i]);
> +        host->irq_num[i] = -1;
> +    }
> +
> +    pci->bus = pci_register_root_bus(dev, "cxlhost.0", cxl_host_set_irq,
> +                                 pci_swizzle_map_irq_fn, host, &host->io_mmio,
> +                                 &host->io_ioport, 0, 4, TYPE_CXL_BUS);
> +    cxlbus = pci->bus;
> +    cxlbus->flags |= PCI_BUS_CXL;
As cxlbus is only used for flags, why not simply
    pci->bus->flags |= PCI_BUS_CXL;

and drop the local variable. Or... 

> +
> +    pci_bus_set_route_irq_fn(pci->bus, cxl_host_route_intx_pin_to_irq);

Use cxlbus here instead of pci->bus giving a second user.

> +}


> diff --git a/include/hw/pci-host/cxl_host_bridge.h b/include/hw/pci-host/cxl_host_bridge.h
> new file mode 100644
> index 0000000000..833e460f01
> --- /dev/null
> +++ b/include/hw/pci-host/cxl_host_bridge.h
> @@ -0,0 +1,23 @@
> +/*
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#include "hw/cxl/cxl.h"
> +#include "hw/irq.h"
> +#include "hw/pci/pcie_host.h"

We should follow approx include what you use principles.
So need the header for MemoryRegion as well here.
"system/memory.h" seems to be most likely choice for that.


> +
> +typedef struct CXLHostBridge {
> +    PCIExpressHost parent_obj;
> +
> +    CXLComponentState cxl_cstate;
> +
> +    MemoryRegion io_ioport;

I'm not sure the io_ prefix is adding much given this is all in
an CXLHostBridge object?

> +    MemoryRegion io_mmio;
> +    MemoryRegion io_ioport_window;
> +    MemoryRegion io_mmio_window;
> +    qemu_irq irq[PCI_NUM_PINS];
> +    int irq_num[PCI_NUM_PINS];
> +} CXLHostBridge;
> +
> +int cxl_host_set_irq_num(CXLHostBridge *host, int index, int gsi);
> +void cxl_host_hook_up_registers(CXLState *cxl_state, CXLHostBridge *host);

Re: [RFC PATCH v3 0/2] cxl: Support creation of a new CXL Host Bridge

[Dave Jiang]

On 6/16/25 9:06 PM, wangyuquan wrote:
> v2 -> v3:
> - Update the commit message
> - Fix some alignment and space problems
> - Add a SPDX header for the new file
> - Remove unnecessary comments
> - Add CXL_HOST_BRIDGE config
> v1 -> v2:
> - Move the code of new bridge to hw/pci-host/cxl.c
> - Fix and simplify some logic on handling the different bridge types

Hi Yuquan, can you please add qemu to your patch subject prefix in the future? i.e. [QEMU PATCH v4 0/2]. It would help the maintainers on linux-cxl to know they are not kernel patches. Thank you!

> 
> Background
> ==========
> Currently the base CXL support for arm platforms is only on Jonathan's
> patches[1]. Some platform like SBSA-REF can be more like a real machine,
> thus the support of CXL could be meaningful. However, the pxb-cxl-host
> realization on this platform seems not satisfying their requirements[2].
> 
> New CXL HOST design
> ===================
> Defines a new CXL host bridge type (TYPE_CXL_HOST). This is an
> independent CXL host bridge which combined GPEX features (ECAM, MMIO
> windows and irq) and CXL Host Bridge Component Registers (CHBCR).
> 
> The root bus path of CXL_HOST is "0001:00", that would not affect the
> original pcie host topology. In the previous, the pxb-cxl-host with
> any CXL root ports and CXL endpoint devices would occupy the BDF
> number of the original pcie domain. This new type provide a solution
> to resolve the problem.
> 
> Remaining problems
> ==================
> I tried to use 'object_resolve_path' but it could not work in
> 'cxl_fmws_link_targets', so I used 'TYPE_DEVICE' to match that.
> 
> Link:
> [1]: https://lore.kernel.org/linux-cxl/20220616141950.23374-1-Jonathan.Cameron@huawei.com/
> [2]: https://lists.nongnu.org/archive/html/qemu-arm/2024-11/msg00522.html
> 
> Yuquan Wang (2):
>   pci-host/cxl: Support creation of a new CXL Host Bridge
>   hw/pxb-cxl: Rename the pxb cxl host bridge
> 
>  hw/cxl/cxl-host-stubs.c               |   3 +
>  hw/cxl/cxl-host.c                     |  64 ++++++++---
>  hw/pci-bridge/pci_expander_bridge.c   |   8 +-
>  hw/pci-host/Kconfig                   |   4 +
>  hw/pci-host/cxl.c                     | 152 ++++++++++++++++++++++++++
>  hw/pci-host/meson.build               |   1 +
>  include/hw/cxl/cxl.h                  |   7 +-
>  include/hw/cxl/cxl_host.h             |   3 +
>  include/hw/pci-host/cxl_host_bridge.h |  23 ++++
>  9 files changed, 244 insertions(+), 21 deletions(-)
>  create mode 100644 hw/pci-host/cxl.c
>  create mode 100644 include/hw/pci-host/cxl_host_bridge.h
>