[PATCH 13/15] iommu/vt-d: Add an irq_chip for posted MSIs

Jacob Pan
2024-01-26T23:37:31Z

Introduce a new irq_chip for posted MSIs, the key difference is in
irq_ack where EOI is performed by the notification handler.

When posted MSI is enabled, MSI domain/chip hierarchy will look like
this example:

domain: IR-PCI-MSIX-0000:50:00.0-12
hwirq: 0x29
chip: IR-PCI-MSIX-0000:50:00.0
flags: 0x430
IRQCHIP_SKIP_SET_WAKE
IRQCHIP_ONESHOT_SAFE
parent:
domain: INTEL-IR-10-13
hwirq: 0x2d0000
chip: INTEL-IR-POST
flags: 0x0
parent:
domain: VECTOR
hwirq: 0x77
chip: APIC

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
---
drivers/iommu/intel/irq_remapping.c | 46 +++++++++++++++++++++++++++++
1 file changed, 46 insertions(+)

diff --git a/drivers/iommu/intel/irq_remapping.c b/drivers/iommu/intel/irq_remapping.c
index 566297bc87dd..fa719936b44e 100644
--- a/drivers/iommu/intel/irq_remapping.c
+++ b/drivers/iommu/intel/irq_remapping.c
@@ -1233,6 +1233,52 @@ static struct irq_chip intel_ir_chip = {
.irq_set_vcpu_affinity = intel_ir_set_vcpu_affinity,
};

+static void dummy(struct irq_data *d)
+{
+}
+
+/*
+ * With posted MSIs, all vectors are multiplexed into a single notification
+ * vector. Devices MSIs are then dispatched in a demux loop where
+ * EOIs can be coalesced as well.
+ *
+ * "INTEL-IR-POST" IRQ chip does not do EOI on ACK, thus the dummy irq_ack()
+ * function. Instead EOI is performed by the posted interrupt notification
+ * handler.
+ *
+ * For the example below, 3 MSIs are coalesced into one CPU notification. Only
+ * one apic_eoi() is needed.
+ *
+ * __sysvec_posted_msi_notification()
+ * irq_enter();
+ * handle_edge_irq()
+ * irq_chip_ack_parent()
+ * dummy(); // No EOI
+ * handle_irq_event()
+ * driver_handler()
+ * irq_enter();
+ * handle_edge_irq()
+ * irq_chip_ack_parent()
+ * dummy(); // No EOI
+ * handle_irq_event()
+ * driver_handler()
+ * irq_enter();
+ * handle_edge_irq()
+ * irq_chip_ack_parent()
+ * dummy(); // No EOI
+ * handle_irq_event()
+ * driver_handler()
+ * apic_eoi()
+ * irq_exit()
+ */
+static struct irq_chip intel_ir_chip_post_msi = {
+ .name = "INTEL-IR-POST",
+ .irq_ack = dummy,
+ .irq_set_affinity = intel_ir_set_affinity,
+ .irq_compose_msi_msg = intel_ir_compose_msi_msg,
+ .irq_set_vcpu_affinity = intel_ir_set_vcpu_affinity,
+};
+
static void fill_msi_msg(struct msi_msg *msg, u32 index, u32 subhandle)
{
memset(msg, 0, sizeof(*msg));
--
2.25.1