[PATCH v3 7/8] ath12k: use KVM MSI domain for VM passthrough

[Jose Ignacio Tornos Martinez <jtornosm@redhat.com>]

The Qualcomm ath12k firmware programs MSI addresses directly into
device BAR registers for CE/SRNG ring interrupt delivery, bypassing
the standard PCI config MSI path managed by QEMU/VFIO. In a VM, the
firmware receives the guest virtual APIC address instead of the host
IRTE address, causing DMAR faults and non-functional interrupts.

When CONFIG_PCI_KVM_MSI_DOMAIN is enabled, use the KVM PCI MSI domain
synchronization functions:

1. In power_up, after msi_enable, call kvm_pci_msi_wait_ready() to
   retrieve and cache the host physical MSI address via KVM hypercall.

2. In ath12k_pci_get_msi_address(), call kvm_pci_msi_get_address() to
   return the cached host MSI address instead of reading from PCI
   config (which contains the guest virtual address in a VM).

Unlike ath11k which caches MSI address once during power_up, ath12k
reads MSI address on-the-fly via get_msi_address() each time rings
are configured. The kvm_pci_msi_get_address() function provides the
cached host values from a previous successful wait_ready call.

On baremetal, if CONFIG_PCI_KVM_MSI_DOMAIN is not enabled the code is
compiled out and the behavior is identical to the original. If
CONFIG_PCI_KVM_MSI_DOMAIN is enabled (e.g. distribution kernels), the
KVM MSI functions detect baremetal at runtime and return immediately,
preserving the original behavior with no side effects.

Signed-off-by: Jose Ignacio Tornos Martinez <jtornosm@redhat.com>
---
v3: new
v2: https://lore.kernel.org/all/20261011074514.515894-1-jtornosm@redhat.com/

 drivers/net/wireless/ath/ath12k/pci.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/net/wireless/ath/ath12k/pci.c b/drivers/net/wireless/ath/ath12k/pci.c
index f7879fb48d32..dbd960f88d38 100644
--- a/drivers/net/wireless/ath/ath12k/pci.c
+++ b/drivers/net/wireless/ath/ath12k/pci.c
@@ -8,6 +8,9 @@
 #include <linux/interrupt.h>
 #include <linux/msi.h>
 #include <linux/pci.h>
+#if IS_ENABLED(CONFIG_PCI_KVM_MSI_DOMAIN)
+#include <linux/pci-kvm-msi.h>
+#endif
 #include <linux/time.h>
 #include <linux/vmalloc.h>
 
@@ -1082,6 +1085,11 @@ void ath12k_pci_get_msi_address(struct ath12k_base *ab, u32 *msi_addr_lo,
 	struct ath12k_pci *ab_pci = ath12k_pci_priv(ab);
 	struct pci_dev *pci_dev = to_pci_dev(ab->dev);
 
+#if IS_ENABLED(CONFIG_PCI_KVM_MSI_DOMAIN)
+	if (kvm_pci_msi_get_address(pci_dev, msi_addr_lo, msi_addr_hi, NULL))
+		return;
+#endif
+
 	pci_read_config_dword(pci_dev, pci_dev->msi_cap + PCI_MSI_ADDRESS_LO,
 			      msi_addr_lo);
 
@@ -1485,6 +1493,10 @@ int ath12k_pci_power_up(struct ath12k_base *ab)
 
 	ath12k_pci_msi_enable(ab_pci);
 
+#if IS_ENABLED(CONFIG_PCI_KVM_MSI_DOMAIN)
+	kvm_pci_msi_wait_ready(ab_pci->pdev, 500);
+#endif
+
 	if (ath12k_fw_feature_supported(ab, ATH12K_FW_FEATURE_MULTI_QRTR_ID))
 		ath12k_pci_update_qrtr_node_id(ab);
 
@@ -1886,3 +1898,6 @@ EXPORT_SYMBOL(ath12k_pci_unregister_driver);
 /* firmware files */
 MODULE_FIRMWARE(ATH12K_FW_DIR "/QCN9274/hw2.0/*");
 MODULE_FIRMWARE(ATH12K_FW_DIR "/WCN7850/hw2.0/*");
+#if IS_ENABLED(CONFIG_PCI_KVM_MSI_DOMAIN)
+MODULE_SOFTDEP("pre: pci-kvm-msi");
+#endif
-- 
2.56.0