Revert "platform/x86: p2sb: Allow p2sb_bar() calls during PCI device probe"

This reverts commit b28ff7a.

The commit introduced P2SB device scan and resource cache during the
boot process to avoid deadlock. But it caused detection failure of
IDE controllers on old systems [1]. The IDE controllers on old systems
and P2SB devices on newer systems have same PCI DEVFN. It is suspected
the confusion between those two is the failure cause. Revert the change
at this moment until the proper solution gets ready.

Link: https://lore.kernel.org/platform-driver-x86/CABq1_vjfyp_B-f4LAL6pg394bP6nDFyvg110TOLHHb0x4aCPeg@mail.gmail.com/T/#m07b30468d9676fc5e3bb2122371121e4559bb383 [1]
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Link: https://lore.kernel.org/r/20240104114050.3142690-1-shinichiro.kawasaki@wdc.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

Author: kawasaki

drivers/platform/x86/p2sb.c

@@ -26,21 +26,6 @@ static const struct x86_cpu_id p2sb_cpu_ids[] = {
 	{}
 };
 
-/*
- * Cache BAR0 of P2SB device functions 0 to 7.
- * TODO: The constant 8 is the number of functions that PCI specification
- *       defines. Same definitions exist tree-wide. Unify this definition and
- *       the other definitions then move to include/uapi/linux/pci.h.
- */
-#define NR_P2SB_RES_CACHE 8
-
-struct p2sb_res_cache {
-	u32 bus_dev_id;
-	struct resource res;
-};
-
-static struct p2sb_res_cache p2sb_resources[NR_P2SB_RES_CACHE];
-
 static int p2sb_get_devfn(unsigned int *devfn)
 {
 	unsigned int fn = P2SB_DEVFN_DEFAULT;
@@ -54,16 +39,8 @@ static int p2sb_get_devfn(unsigned int *devfn)
 	return 0;
 }
 
-static bool p2sb_valid_resource(struct resource *res)
-{
-	if (res->flags)
-		return true;
-
-	return false;
-}
-
 /* Copy resource from the first BAR of the device in question */
-static void p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem)
+static int p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem)
 {
 	struct resource *bar0 = &pdev->resource[0];
 
@@ -79,64 +56,47 @@ static void p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem)
 	mem->end = bar0->end;
 	mem->flags = bar0->flags;
 	mem->desc = bar0->desc;
+
+	return 0;
 }
 
-static void p2sb_scan_and_cache_devfn(struct pci_bus *bus, unsigned int devfn)
+static int p2sb_scan_and_read(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
 {
-	struct p2sb_res_cache *cache = &p2sb_resources[PCI_FUNC(devfn)];
 	struct pci_dev *pdev;
+	int ret;
 
 	pdev = pci_scan_single_device(bus, devfn);
 	if (!pdev)
-		return;
+		return -ENODEV;
 
-	p2sb_read_bar0(pdev, &cache->res);
-	cache->bus_dev_id = bus->dev.id;
+	ret = p2sb_read_bar0(pdev, mem);
 
 	pci_stop_and_remove_bus_device(pdev);
-	return;
-}
-
-static int p2sb_scan_and_cache(struct pci_bus *bus, unsigned int devfn)
-{
-	unsigned int slot, fn;
-
-	if (PCI_FUNC(devfn) == 0) {
-		/*
-		 * When function number of the P2SB device is zero, scan it and
-		 * other function numbers, and if devices are available, cache
-		 * their BAR0s.
-		 */
-		slot = PCI_SLOT(devfn);
-		for (fn = 0; fn < NR_P2SB_RES_CACHE; fn++)
-			p2sb_scan_and_cache_devfn(bus, PCI_DEVFN(slot, fn));
-	} else {
-		/* Scan the P2SB device and cache its BAR0 */
-		p2sb_scan_and_cache_devfn(bus, devfn);
-	}
-
-	if (!p2sb_valid_resource(&p2sb_resources[PCI_FUNC(devfn)].res))
-		return -ENOENT;
-
-	return 0;
-}
-
-static struct pci_bus *p2sb_get_bus(struct pci_bus *bus)
-{
-	static struct pci_bus *p2sb_bus;
-
-	bus = bus ?: p2sb_bus;
-	if (bus)
-		return bus;
-
-	/* Assume P2SB is on the bus 0 in domain 0 */
-	p2sb_bus = pci_find_bus(0, 0);
-	return p2sb_bus;
+	return ret;
 }
 
-static int p2sb_cache_resources(void)
+/**
+ * p2sb_bar - Get Primary to Sideband (P2SB) bridge device BAR
+ * @bus: PCI bus to communicate with
+ * @devfn: PCI slot and function to communicate with
+ * @mem: memory resource to be filled in
+ *
+ * The BIOS prevents the P2SB device from being enumerated by the PCI
+ * subsystem, so we need to unhide and hide it back to lookup the BAR.
+ *
+ * if @bus is NULL, the bus 0 in domain 0 will be used.
+ * If @devfn is 0, it will be replaced by devfn of the P2SB device.
+ *
+ * Caller must provide a valid pointer to @mem.
+ *
+ * Locking is handled by pci_rescan_remove_lock mutex.
+ *
+ * Return:
+ * 0 on success or appropriate errno value on error.
+ */
+int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
 {
-	struct pci_bus *bus;
+	struct pci_dev *pdev_p2sb;
 	unsigned int devfn_p2sb;
 	u32 value = P2SBC_HIDE;
 	int ret;
@@ -146,89 +106,39 @@ static int p2sb_cache_resources(void)
 	if (ret)
 		return ret;
 
-	bus = p2sb_get_bus(NULL);
-	if (!bus)
-		return -ENODEV;
+	/* if @bus is NULL, use bus 0 in domain 0 */
+	bus = bus ?: pci_find_bus(0, 0);
 
 	/*
 	 * Prevent concurrent PCI bus scan from seeing the P2SB device and
 	 * removing via sysfs while it is temporarily exposed.
 	 */
 	pci_lock_rescan_remove();
 
-	/*
-	 * The BIOS prevents the P2SB device from being enumerated by the PCI
-	 * subsystem, so we need to unhide and hide it back to lookup the BAR.
-	 * Unhide the P2SB device here, if needed.
-	 */
+	/* Unhide the P2SB device, if needed */
 	pci_bus_read_config_dword(bus, devfn_p2sb, P2SBC, &value);
 	if (value & P2SBC_HIDE)
 		pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, 0);
 
-	ret = p2sb_scan_and_cache(bus, devfn_p2sb);
+	pdev_p2sb = pci_scan_single_device(bus, devfn_p2sb);
+	if (devfn)
+		ret = p2sb_scan_and_read(bus, devfn, mem);
+	else
+		ret = p2sb_read_bar0(pdev_p2sb, mem);
+	pci_stop_and_remove_bus_device(pdev_p2sb);
 
 	/* Hide the P2SB device, if it was hidden */
 	if (value & P2SBC_HIDE)
 		pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, P2SBC_HIDE);
 
 	pci_unlock_rescan_remove();
 
-	return ret;
-}
-
-/**
- * p2sb_bar - Get Primary to Sideband (P2SB) bridge device BAR
- * @bus: PCI bus to communicate with
- * @devfn: PCI slot and function to communicate with
- * @mem: memory resource to be filled in
- *
- * If @bus is NULL, the bus 0 in domain 0 will be used.
- * If @devfn is 0, it will be replaced by devfn of the P2SB device.
- *
- * Caller must provide a valid pointer to @mem.
- *
- * Return:
- * 0 on success or appropriate errno value on error.
- */
-int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
-{
-	struct p2sb_res_cache *cache;
-	int ret;
-
-	bus = p2sb_get_bus(bus);
-	if (!bus)
-		return -ENODEV;
-
-	if (!devfn) {
-		ret = p2sb_get_devfn(&devfn);
-		if (ret)
-			return ret;
-	}
+	if (ret)
+		return ret;
 
-	cache = &p2sb_resources[PCI_FUNC(devfn)];
-	if (cache->bus_dev_id != bus->dev.id)
+	if (mem->flags == 0)
 		return -ENODEV;
 
-	if (!p2sb_valid_resource(&cache->res))
-		return -ENOENT;
-
-	memcpy(mem, &cache->res, sizeof(*mem));
 	return 0;
 }
 EXPORT_SYMBOL_GPL(p2sb_bar);
-
-static int __init p2sb_fs_init(void)
-{
-	p2sb_cache_resources();
-	return 0;
-}
-
-/*
- * pci_rescan_remove_lock to avoid access to unhidden P2SB devices can
- * not be locked in sysfs pci bus rescan path because of deadlock. To
- * avoid the deadlock, access to P2SB devices with the lock at an early
- * step in kernel initialization and cache required resources. This
- * should happen after subsys_initcall which initializes PCI subsystem
- * and before device_initcall which requires P2SB resources.
- */
-fs_initcall(p2sb_fs_init);