pcie: enable Extended tag field support

>From what I read PCI has 32 transactions, PCI Express devices can handle
256 with Extended tag enabled (spec mentions also larger values but I
lack PCIe knowledge).

QEMU leaves 'Extended tag field' with 0 as value:

Capabilities: [e0] Express (v1) Root Complex Integrated Endpoint, IntMsgNum 0
        DevCap: MaxPayload 128 bytes, PhantFunc 0
                ExtTag- RBE+ FLReset- TEE-IO-

SBSA ACS has test 824 which checks for PCIe device capabilities. BSA
specification [1] (SBSA is on top of BSA) in section F.3.2 lists
expected values for Device Capabilities Register:

Device Capabilities Register     Requirement
Role based error reporting       RCEC and RCiEP: Hardwired to 1
Endpoint L0s acceptable latency  RCEC and RCiEP: Hardwired to 0
L1 acceptable latency            RCEC and RCiEP: Hardwired to 0
Captured slot power limit scale  RCEC and RCiEP: Hardwired to 0
Captured slot power limit value  RCEC and RCiEP: Hardwired to 0
Max payload size                 value must be compliant with PCIe spec
Phantom functions                RCEC and RCiEP: Recommendation is to
                                 hardwire this bit to 0.
Extended tag field               Hardwired to 1

1. https://developer.arm.com/documentation/den0094/c/

This change enables Extended tag field. All versioned platforms should
have it disabled for older versions (tested with Arm/virt).

Signed-off-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
Message-Id: <20241023113820.486017-1-marcin.juszkiewicz@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/core/machine.c

@@ -34,7 +34,9 @@
 #include "hw/virtio/virtio-iommu.h"
 #include "audio/audio.h"
 
-GlobalProperty hw_compat_9_1[] = {};
+GlobalProperty hw_compat_9_1[] = {
+    { TYPE_PCI_DEVICE, "x-pcie-ext-tag", "false" },
+};
 const size_t hw_compat_9_1_len = G_N_ELEMENTS(hw_compat_9_1);
 
 GlobalProperty hw_compat_9_0[] = {

hw/pci/pci.c

@@ -100,6 +100,8 @@ static Property pci_props[] = {
                     QEMU_PCIE_ARI_NEXTFN_1_BITNR, false),
     DEFINE_PROP_SIZE32("x-max-bounce-buffer-size", PCIDevice,
                      max_bounce_buffer_size, DEFAULT_MAX_BOUNCE_BUFFER_SIZE),
+    DEFINE_PROP_BIT("x-pcie-ext-tag", PCIDevice, cap_present,
+                    QEMU_PCIE_EXT_TAG_BITNR, true),
     { .name = "busnr", .info = &prop_pci_busnr },
     DEFINE_PROP_END_OF_LIST()
 };

hw/pci/pcie.c

@@ -86,7 +86,13 @@ pcie_cap_v1_fill(PCIDevice *dev, uint8_t port, uint8_t type, uint8_t version)
      * Specification, Revision 1.1., or subsequent PCI Express Base
      * Specification revisions.
      */
-    pci_set_long(exp_cap + PCI_EXP_DEVCAP, PCI_EXP_DEVCAP_RBER);
+    uint32_t devcap = PCI_EXP_DEVCAP_RBER;
+
+    if (dev->cap_present & QEMU_PCIE_EXT_TAG) {
+        devcap = PCI_EXP_DEVCAP_RBER | PCI_EXP_DEVCAP_EXT_TAG;
+    }
+
+    pci_set_long(exp_cap + PCI_EXP_DEVCAP, devcap);
 
     pci_set_long(exp_cap + PCI_EXP_LNKCAP,
                  (port << PCI_EXP_LNKCAP_PN_SHIFT) |

include/hw/pci/pci.h

@@ -214,6 +214,8 @@ enum {
     QEMU_PCIE_ERR_UNC_MASK = (1 << QEMU_PCIE_ERR_UNC_MASK_BITNR),
 #define QEMU_PCIE_ARI_NEXTFN_1_BITNR 12
     QEMU_PCIE_ARI_NEXTFN_1 = (1 << QEMU_PCIE_ARI_NEXTFN_1_BITNR),
+#define QEMU_PCIE_EXT_TAG_BITNR 13
+    QEMU_PCIE_EXT_TAG = (1 << QEMU_PCIE_EXT_TAG_BITNR),
 };
 
 typedef struct PCIINTxRoute {