From c0b1a2d6c0e0009a32755911b2a2f65de0e50986 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Thu, 18 Sep 2025 13:47:21 -0400
Subject: kern: pci: Add initial bus enumeration

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 src/sys/include/io/pci/pci.h |  4 +++
 src/sys/io/pci/pci.c         | 81 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 85 insertions(+)

diff --git a/src/sys/include/io/pci/pci.h b/src/sys/include/io/pci/pci.h
index a636ce7..8f65aa3 100644
--- a/src/sys/include/io/pci/pci.h
+++ b/src/sys/include/io/pci/pci.h
@@ -43,11 +43,15 @@ typedef uint32_t pcival_t;
  * @bus: Bus number of device
  * @slot: Slot number of device
  * @func: Function number of device
+ * @vendor: Vendor ID
+ * @device: Device ID
  */
 struct pci_device {
     uint16_t bus;
     uint8_t slot;
     uint8_t func;
+    uint16_t vendor;
+    uint16_t device;
 };
 
 /*
diff --git a/src/sys/io/pci/pci.c b/src/sys/io/pci/pci.c
index 864e4c3..a4bf125 100644
--- a/src/sys/io/pci/pci.c
+++ b/src/sys/io/pci/pci.c
@@ -35,8 +35,87 @@
 #include <io/pci/pci.h>
 #include <io/pci/cam.h>
 
+#define PCI_BUS_ROOT 0
+
 static struct cam_hook cam;
 
+/*
+ * Attempt to register a PCI device and bail
+ * if it doesn't exist on the bus.
+ */
+static void
+pci_register_dev(struct pci_device *dev)
+{
+    pcireg_t vend_dev;
+    uint16_t device_id;
+    uint16_t vendor_id;
+
+    if (dev == NULL) {
+        return;
+    }
+
+    /* Get the vendor and device ID */
+    vend_dev = pci_readl(dev, PCIREG_VENDOR_ID);
+    vendor_id = vend_dev & 0xFFFF;
+    device_id = (vendor_id >> 16) & 0xFFFF;
+
+    /* Does this device exist? */
+    if (vendor_id == 0xFFFF) {
+        return;
+    }
+
+    /*
+     * Log out the BDF notation as well as vendor,
+     * and logical slot ID.
+     */
+    printf(
+        "bridge: device @ pci <%x.%x.%x>\n",
+        dev->bus, dev->slot,
+        dev->func, dev->vendor,
+        dev->slot
+    );
+}
+
+/*
+ * Enumerate a specifc bus of its devices
+ *
+ * @bus: Bus to enumerate
+ */
+static void
+pci_enum_bus(uint16_t bus)
+{
+    pcireg_t reg;
+    struct pci_device dev;
+    if (bus > 256) {
+        printf("pci_enum_bus: bad bus number %x\n", bus);
+        return;
+    }
+
+    dev.bus = bus;
+    for (int slot = 0; slot < 32; ++slot) {
+        dev.slot = slot;
+        dev.func = 0;
+        reg = pci_readl(&dev, PCIREG_HDRTYPE);
+
+        /*
+         * Section 6.2.1 of the PCI spec states that some
+         * devices may only implement a single function.
+         * We can check this with bit 7 of the header type
+         * register. If we read a 1, it is a multifunction
+         * device.
+         */
+        if (!ISSET(reg, BIT(7))) {
+            pci_register_dev(&dev);
+            continue;
+        }
+
+        for (uint8_t func = 0; func < 8; ++func) {
+            pci_register_dev(&dev);
+            ++dev.func;
+        }
+    }
+}
+
 /*
  * Read from a specific register
  */
@@ -73,4 +152,6 @@ pci_init_bus(void)
         printf("pci_init_bus: pci_cam_init() returned %d\n", error);
         panic("pci_init_bus: failed to init CAM\n");
     }
+
+    pci_enum_bus(PCI_BUS_ROOT);
 }
-- 
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