[PATCH v7 4/4] PCI: endpoint: Add NTB MSI support

[Frank Li]

                        ┌───────┐           ┌──────────┐
                        │       │           │          │
      ┌─────────────┐   │       │           │ PCI Host │
      │ MSI         │◄┐ │       │           │          │
      │ Controller  │ │ │       │ MSI Write │          │
      └─────────────┘ └─┼───────┼───────────┼─BAR0     │
                        │ PCI   │           │ BAR1     │
                        │ EP    │           │ BAR2     │
                        │       │           │ BAR3     │
                        │       │           │ BAR4     │
                        │       ├──────────►│          │
                        └───────┘           └──────────┘

Linux supports endpoint functions. PCI RC write BAR<n> space like write
to memory. The EP side can't know memory changed by the host driver.

PCI Spec has not defined a standard method to do that. Only define MSI(x)
to let EP notified RC status change.

The basic idea is to trigger an IRQ when PCI RC writes to a memory
address. That's what MSI controller provided. EP drivers just need to
request a platform MSI interrupt, struct msi_msg *msg will pass down a
memory address and data. EP driver will map such memory address to one of
PCI BAR<n>.  PCI RC writes to such memory to trigger EP side IRQ.

Add MSI support for pci-epf-vntb. Query if system has an MSI controller.
Set up doorbell address according to struct msi_msg.

So PCI RC can write this doorbell address to trigger EP side's IRQ.

If no MSI controller exists, fall back to software polling.

Signed-off-by: Frank Li <Frank.Li@xxxxxxx>
---
 drivers/pci/endpoint/functions/pci-epf-vntb.c | 148 +++++++++++++++---
 1 file changed, 122 insertions(+), 26 deletions(-)

diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
index 1466dd1904175..f6e0b682da000 100644
--- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
+++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
@@ -44,6 +44,7 @@
 #include <linux/pci-epc.h>
 #include <linux/pci-epf.h>
 #include <linux/ntb.h>
+#include <linux/msi.h>
 
 static struct workqueue_struct *kpcintb_workqueue;
 
@@ -143,6 +144,8 @@ struct epf_ntb {
 	void __iomem *vpci_mw_addr[MAX_MW];
 
 	struct delayed_work cmd_handler;
+
+	int msi_virqbase;
 };
 
 #define to_epf_ntb(epf_group) container_of((epf_group), struct epf_ntb, group)
@@ -253,13 +256,15 @@ static void epf_ntb_cmd_handler(struct work_struct *work)
 
 	ntb = container_of(work, struct epf_ntb, cmd_handler.work);
 
-	for (i = 1; i < ntb->db_count; i++) {
-		if (readl(ntb->epf_db + i * 4)) {
-			if (readl(ntb->epf_db + i * 4))
-				ntb->db |= 1 << (i - 1);
+	if (!ntb->epf_db_phy) {
+		for (i = 1; i < ntb->db_count; i++) {
+			if (readl(ntb->epf_db + i * 4)) {
+				if (readl(ntb->epf_db + i * 4))
+					ntb->db |= 1 << (i - 1);
 
-			ntb_db_event(&ntb->ntb, i);
-			writel(0, ntb->epf_db + i * 4);
+				ntb_db_event(&ntb->ntb, i);
+				writel(0, ntb->epf_db + i * 4);
+			}
 		}
 	}
 
@@ -454,11 +459,9 @@ static int epf_ntb_config_spad_bar_alloc(struct epf_ntb *ntb)
 	ctrl->num_mws = ntb->num_mws;
 	ntb->spad_size = spad_size;
 
-	ctrl->db_entry_size = 4;
-
 	for (i = 0; i < ntb->db_count; i++) {
 		ntb->reg->db_data[i] = 1 + i;
-		ntb->reg->db_offset[i] = 0;
+		ntb->reg->db_offset[i] = 4 * i;
 	}
 
 	return 0;
@@ -509,6 +512,28 @@ static int epf_ntb_configure_interrupt(struct epf_ntb *ntb)
 	return 0;
 }
 
+static int epf_ntb_db_size(struct epf_ntb *ntb)
+{
+	const struct pci_epc_features *epc_features;
+	size_t size = 4 * ntb->db_count;
+	u32 align;
+
+	epc_features = pci_epc_get_features(ntb->epf->epc,
+					    ntb->epf->func_no,
+					    ntb->epf->vfunc_no);
+	align = epc_features->align;
+
+	if (size < 128)
+		size = 128;
+
+	if (align)
+		size = ALIGN(size, align);
+	else
+		size = roundup_pow_of_two(size);
+
+	return size;
+}
+
 /**
  * epf_ntb_db_bar_init() - Configure Doorbell window BARs
  * @ntb: NTB device that facilitates communication between HOST and vHOST
@@ -522,33 +547,32 @@ static int epf_ntb_db_bar_init(struct epf_ntb *ntb)
 	struct pci_epf_bar *epf_bar;
 	void __iomem *mw_addr;
 	enum pci_barno barno;
-	size_t size = 4 * ntb->db_count;
+	size_t size;
 
 	epc_features = pci_epc_get_features(ntb->epf->epc,
 					    ntb->epf->func_no,
 					    ntb->epf->vfunc_no);
 	align = epc_features->align;
-
-	if (size < 128)
-		size = 128;
-
-	if (align)
-		size = ALIGN(size, align);
-	else
-		size = roundup_pow_of_two(size);
+	size = epf_ntb_db_size(ntb);
 
 	barno = ntb->epf_ntb_bar[BAR_DB];
+	epf_bar = &ntb->epf->bar[barno];
 
-	mw_addr = pci_epf_alloc_space(ntb->epf, size, barno, align, 0);
-	if (!mw_addr) {
-		dev_err(dev, "Failed to allocate OB address\n");
-		return -ENOMEM;
+	if (ntb->epf_db_phy) {
+		mw_addr = NULL;
+		epf_bar->phys_addr = ntb->epf_db_phy;
+		epf_bar->barno = barno;
+		epf_bar->size = size;
+	} else {
+		mw_addr = pci_epf_alloc_space(ntb->epf, size, barno, align, 0);
+		if (!mw_addr) {
+			dev_err(dev, "Failed to allocate OB address\n");
+			return -ENOMEM;
+		}
 	}
 
 	ntb->epf_db = mw_addr;
 
-	epf_bar = &ntb->epf->bar[barno];
-
 	ret = pci_epc_set_bar(ntb->epf->epc, ntb->epf->func_no, ntb->epf->vfunc_no, epf_bar);
 	if (ret) {
 		dev_err(dev, "Doorbell BAR set failed\n");
@@ -704,6 +728,77 @@ static int epf_ntb_init_epc_bar(struct epf_ntb *ntb)
 	return 0;
 }
 
+static void epf_ntb_write_msi_msg(struct msi_desc *desc, struct msi_msg *msg)
+{
+	struct epf_ntb *ntb = dev_get_drvdata(desc->dev);
+	struct epf_ntb_ctrl *reg = ntb->reg;
+	int size = epf_ntb_db_size(ntb);
+	u64 addr;
+
+	addr = msg->address_hi;
+	addr <<= 32;
+	addr |= msg->address_lo;
+
+	reg->db_data[desc->msi_index] = msg->data;
+
+	if (desc->msi_index == 0)
+		ntb->epf_db_phy = round_down(addr, size);
+
+	reg->db_offset[desc->msi_index] = addr - ntb->epf_db_phy;
+}
+
+static irqreturn_t epf_ntb_interrupt_handler(int irq, void *data)
+{
+	struct epf_ntb *ntb = data;
+	int index;
+
+	index = irq - ntb->msi_virqbase;
+	ntb->db |= 1 << (index - 1);
+	ntb_db_event(&ntb->ntb, index);
+
+	return IRQ_HANDLED;
+}
+
+static void epf_ntb_epc_msi_init(struct epf_ntb *ntb)
+{
+	struct device *dev = &ntb->epf->dev;
+	struct irq_domain *domain;
+	int virq;
+	int ret;
+	int i;
+
+	domain = dev_get_msi_domain(ntb->epf->epc->dev.parent);
+	if (!domain)
+		return;
+
+	dev_set_msi_domain(dev, domain);
+
+	if (platform_msi_domain_alloc_irqs(&ntb->epf->dev,
+		ntb->db_count,
+		epf_ntb_write_msi_msg)) {
+		dev_info(dev, "Can't allocate MSI, fall back to poll mode\n");
+		return;
+	}
+
+	dev_info(dev, "vntb use MSI as doorbell\n");
+
+	for (i = 0; i < ntb->db_count; i++) {
+		virq = msi_get_virq(dev, i);
+		ret = devm_request_irq(dev, virq,
+			       epf_ntb_interrupt_handler, 0,
+			       "ntb", ntb);
+
+		if (ret) {
+			dev_err(dev, "devm_request_irq() failure, fall back to poll mode\n");
+			ntb->epf_db_phy = 0;
+			break;
+		}
+
+		if (!i)
+			ntb->msi_virqbase = virq;
+	}
+}
+
 /**
  * epf_ntb_epc_init() - Initialize NTB interface
  * @ntb: NTB device that facilitates communication between HOST and vHOST2
@@ -1299,14 +1394,15 @@ static int epf_ntb_bind(struct pci_epf *epf)
 		goto err_bar_alloc;
 	}
 
+	epf_set_drvdata(epf, ntb);
+	epf_ntb_epc_msi_init(ntb);
+
 	ret = epf_ntb_epc_init(ntb);
 	if (ret) {
 		dev_err(dev, "Failed to initialize EPC\n");
 		goto err_bar_alloc;
 	}
 
-	epf_set_drvdata(epf, ntb);
-
 	pci_space[0] = (ntb->vntb_pid << 16) | ntb->vntb_vid;
 	pci_vntb_table[0].vendor = ntb->vntb_vid;
 	pci_vntb_table[0].device = ntb->vntb_pid;
-- 
2.35.1