PCI: endpoint: pci-epf-vntb: Add MSI doorbell support

Add MSI doorbell support to reduce latency between PCI host and EP.

Before this change:
  ping 169.254.172.137
  64 bytes from 169.254.172.137: icmp_seq=1 ttl=64 time=0.575 ms
  64 bytes from 169.254.172.137: icmp_seq=2 ttl=64 time=1.80 ms
  64 bytes from 169.254.172.137: icmp_seq=3 ttl=64 time=8.19 ms
  64 bytes from 169.254.172.137: icmp_seq=4 ttl=64 time=2.00 ms

After this change:
  ping 169.254.144.71
  64 bytes from 169.254.144.71: icmp_seq=1 ttl=64 time=0.215 ms
  64 bytes from 169.254.144.71: icmp_seq=2 ttl=64 time=0.456 ms
  64 bytes from 169.254.144.71: icmp_seq=3 ttl=64 time=0.448 ms

Also, change the data type of 'epf_ntb::db' to 'atomic_64' as multiple
doorbell interrupts might trigger at the same time.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
[mani: added 'pci_epf_' prefix to doorbell IRQ name, minor code cleanups]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20251015-vntb_msi_doorbell-v6-4-9230298b1910@nxp.com

diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
index 83e9ab10f9c4fc2b485d5463faa2172500f12999..3ecc5059f92b31de1f755bf2e7a22fd04741231e 100644 (file)
--- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
+++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
@@ -36,11 +36,13 @@
  * PCIe Root Port                        PCI EP
  */
 
+#include <linux/atomic.h>
 #include <linux/delay.h>
 #include <linux/io.h>
 #include <linux/module.h>
 #include <linux/slab.h>
 
+#include <linux/pci-ep-msi.h>
 #include <linux/pci-epc.h>
 #include <linux/pci-epf.h>
 #include <linux/ntb.h>
@@ -126,12 +128,13 @@ struct epf_ntb {
        u32 db_count;
        u32 spad_count;
        u64 mws_size[MAX_MW];
-       u64 db;
+       atomic64_t db;
        u32 vbus_number;
        u16 vntb_pid;
        u16 vntb_vid;
 
        bool linkup;
+       bool msi_doorbell;
        u32 spad_size;
 
        enum pci_barno epf_ntb_bar[VNTB_BAR_NUM];
@@ -258,9 +261,9 @@ 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++) {
+       for (i = 1; i < ntb->db_count && !ntb->msi_doorbell; i++) {
                if (ntb->epf_db[i]) {
-                       ntb->db |= 1 << (i - 1);
+                       atomic64_or(1 << (i - 1), &ntb->db);
                        ntb_db_event(&ntb->ntb, i);
                        ntb->epf_db[i] = 0;
                }
@@ -319,7 +322,21 @@ static void epf_ntb_cmd_handler(struct work_struct *work)
 
 reset_handler:
        queue_delayed_work(kpcintb_workqueue, &ntb->cmd_handler,
-                          msecs_to_jiffies(5));
+                          ntb->msi_doorbell ? msecs_to_jiffies(500) : msecs_to_jiffies(5));
+}
+
+static irqreturn_t epf_ntb_doorbell_handler(int irq, void *data)
+{
+       struct epf_ntb *ntb = data;
+       int i;
+
+       for (i = 1; i < ntb->db_count; i++)
+               if (irq == ntb->epf->db_msg[i].virq) {
+                       atomic64_or(1 << (i - 1), &ntb->db);
+                       ntb_db_event(&ntb->ntb, i);
+               }
+
+       return IRQ_HANDLED;
 }
 
 /**
@@ -500,6 +517,94 @@ static int epf_ntb_configure_interrupt(struct epf_ntb *ntb)
        return 0;
 }
 
+static int epf_ntb_db_bar_init_msi_doorbell(struct epf_ntb *ntb,
+                                           struct pci_epf_bar *db_bar,
+                                           const struct pci_epc_features *epc_features,
+                                           enum pci_barno barno)
+{
+       struct pci_epf *epf = ntb->epf;
+       dma_addr_t low, high;
+       struct msi_msg *msg;
+       size_t sz;
+       int ret;
+       int i;
+
+       ret = pci_epf_alloc_doorbell(epf,  ntb->db_count);
+       if (ret)
+               return ret;
+
+       for (i = 0; i < ntb->db_count; i++) {
+               ret = request_irq(epf->db_msg[i].virq, epf_ntb_doorbell_handler,
+                                 0, "pci_epf_vntb_db", ntb);
+
+               if (ret) {
+                       dev_err(&epf->dev,
+                               "Failed to request doorbell IRQ: %d\n",
+                               epf->db_msg[i].virq);
+                       goto err_free_irq;
+               }
+       }
+
+       msg = &epf->db_msg[0].msg;
+
+       high = 0;
+       low = (u64)msg->address_hi << 32 | msg->address_lo;
+
+       for (i = 0; i < ntb->db_count; i++) {
+               struct msi_msg *msg = &epf->db_msg[i].msg;
+               dma_addr_t addr = (u64)msg->address_hi << 32 | msg->address_lo;
+
+               low = min(low, addr);
+               high = max(high, addr);
+       }
+
+       sz = high - low + sizeof(u32);
+
+       ret = pci_epf_assign_bar_space(epf, sz, barno, epc_features, 0, low);
+       if (ret) {
+               dev_err(&epf->dev, "Failed to assign Doorbell BAR space\n");
+               goto err_free_irq;
+       }
+
+       ret = pci_epc_set_bar(ntb->epf->epc, ntb->epf->func_no,
+                             ntb->epf->vfunc_no, db_bar);
+       if (ret) {
+               dev_err(&epf->dev, "Failed to set Doorbell BAR\n");
+               goto err_free_irq;
+       }
+
+       for (i = 0; i < ntb->db_count; i++) {
+               struct msi_msg *msg = &epf->db_msg[i].msg;
+               dma_addr_t addr;
+               size_t offset;
+
+               ret = pci_epf_align_inbound_addr(epf, db_bar->barno,
+                               ((u64)msg->address_hi << 32) | msg->address_lo,
+                               &addr, &offset);
+
+               if (ret) {
+                       ntb->msi_doorbell = false;
+                       goto err_free_irq;
+               }
+
+               ntb->reg->db_data[i] = msg->data;
+               ntb->reg->db_offset[i] = offset;
+       }
+
+       ntb->reg->db_entry_size = 0;
+
+       ntb->msi_doorbell = true;
+
+       return 0;
+
+err_free_irq:
+       for (i--; i >= 0; i--)
+               free_irq(epf->db_msg[i].virq, ntb);
+
+       pci_epf_free_doorbell(ntb->epf);
+       return ret;
+}
+
 /**
  * epf_ntb_db_bar_init() - Configure Doorbell window BARs
  * @ntb: NTB device that facilitates communication between HOST and VHOST
@@ -520,21 +625,25 @@ static int epf_ntb_db_bar_init(struct epf_ntb *ntb)
                                            ntb->epf->func_no,
                                            ntb->epf->vfunc_no);
        barno = ntb->epf_ntb_bar[BAR_DB];
-
-       mw_addr = pci_epf_alloc_space(ntb->epf, size, barno, epc_features, 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);
+       ret = epf_ntb_db_bar_init_msi_doorbell(ntb, epf_bar, epc_features, barno);
        if (ret) {
-               dev_err(dev, "Doorbell BAR set failed\n");
+               /* fall back to polling mode */
+               mw_addr = pci_epf_alloc_space(ntb->epf, size, barno, epc_features, 0);
+               if (!mw_addr) {
+                       dev_err(dev, "Failed to allocate OB address\n");
+                       return -ENOMEM;
+               }
+
+               ntb->epf_db = mw_addr;
+
+               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");
                        goto err_alloc_peer_mem;
+               }
        }
        return ret;
 
@@ -554,6 +663,16 @@ static void epf_ntb_db_bar_clear(struct epf_ntb *ntb)
 {
        enum pci_barno barno;
 
+       if (ntb->msi_doorbell) {
+               int i;
+
+               for (i = 0; i < ntb->db_count; i++)
+                       free_irq(ntb->epf->db_msg[i].virq, ntb);
+       }
+
+       if (ntb->epf->db_msg)
+               pci_epf_free_doorbell(ntb->epf);
+
        barno = ntb->epf_ntb_bar[BAR_DB];
        pci_epf_free_space(ntb->epf, ntb->epf_db, barno, 0);
        pci_epc_clear_bar(ntb->epf->epc,
@@ -1268,7 +1387,7 @@ static u64 vntb_epf_db_read(struct ntb_dev *ndev)
 {
        struct epf_ntb *ntb = ntb_ndev(ndev);
 
-       return ntb->db;
+       return atomic64_read(&ntb->db);
 }
 
 static int vntb_epf_mw_get_align(struct ntb_dev *ndev, int pidx, int idx,
@@ -1308,7 +1427,7 @@ static int vntb_epf_db_clear(struct ntb_dev *ndev, u64 db_bits)
 {
        struct epf_ntb *ntb = ntb_ndev(ndev);
 
-       ntb->db &= ~db_bits;
+       atomic64_and(~db_bits, &ntb->db);
        return 0;
 }