p2sb: Do not scan and remove the P2SB device when it is unhidden

When drivers access P2SB device resources, it calls p2sb_bar(). Before
the commit 5913320 ("platform/x86: p2sb: Allow p2sb_bar() calls
during PCI device probe"), p2sb_bar() obtained the resources and then
called pci_stop_and_remove_bus_device() for clean up. Then the P2SB
device disappeared. The commit 5913320 introduced the P2SB device
resource cache feature in the boot process. During the resource cache,
pci_stop_and_remove_bus_device() is called for the P2SB device, then the
P2SB device disappears regardless of whether p2sb_bar() is called or
not. Such P2SB device disappearance caused a confusion [1]. To avoid the
confusion, avoid the pci_stop_and_remove_bus_device() call when the BIOS
does not hide the P2SB device.

For that purpose, cache the P2SB device resources only if the BIOS hides
the P2SB device. Call p2sb_scan_and_cache() only if p2sb_hidden_by_bios
is true. This allows removing two branches from p2sb_scan_and_cache().
When p2sb_bar() is called, get the resources from the cache if the P2SB
device is hidden. Otherwise, read the resources from the unhidden P2SB
device.

Reported-by: Daniel Walker (danielwa) <danielwa@cisco.com>
Closes: https://lore.kernel.org/lkml/ZzTI+biIUTvFT6NC@goliath/ [1]
Fixes: 5913320 ("platform/x86: p2sb: Allow p2sb_bar() calls during PCI device probe")
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20241128002836.373745-5-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

@@ -101,10 +101,8 @@ static int p2sb_scan_and_cache(struct pci_bus *bus, unsigned int devfn)
 	/*
 	 * 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.
 	 */
-	if (p2sb_hidden_by_bios)
-		pci_bus_write_config_dword(bus, devfn, P2SBC, 0);
+	pci_bus_write_config_dword(bus, devfn, P2SBC, 0);
 
 	/* Scan the P2SB device and cache its BAR0 */
 	p2sb_scan_and_cache_devfn(bus, devfn);
@@ -113,9 +111,7 @@ static int p2sb_scan_and_cache(struct pci_bus *bus, unsigned int devfn)
 	if (devfn == P2SB_DEVFN_GOLDMONT)
 		p2sb_scan_and_cache_devfn(bus, SPI_DEVFN_GOLDMONT);
 
-	/* Hide the P2SB device, if it was hidden */
-	if (p2sb_hidden_by_bios)
-		pci_bus_write_config_dword(bus, devfn, P2SBC, P2SBC_HIDE);
+	pci_bus_write_config_dword(bus, devfn, P2SBC, P2SBC_HIDE);
 
 	if (!p2sb_valid_resource(&p2sb_resources[PCI_FUNC(devfn)].res))
 		return -ENOENT;
@@ -142,7 +138,7 @@ static int p2sb_cache_resources(void)
 	u32 value = P2SBC_HIDE;
 	struct pci_bus *bus;
 	u16 class;
-	int ret;
+	int ret = 0;
 
 	/* Get devfn for P2SB device itself */
 	p2sb_get_devfn(&devfn_p2sb);
@@ -168,7 +164,12 @@ static int p2sb_cache_resources(void)
 	pci_bus_read_config_dword(bus, devfn_p2sb, P2SBC, &value);
 	p2sb_hidden_by_bios = value & P2SBC_HIDE;
 
-	ret = p2sb_scan_and_cache(bus, devfn_p2sb);
+	/*
+	 * If the BIOS does not hide the P2SB device then its resources
+	 * are accesilble. Cache them only if the P2SB device is hidden.
+	 */
+	if (p2sb_hidden_by_bios)
+		ret = p2sb_scan_and_cache(bus, devfn_p2sb);
 
 	pci_unlock_rescan_remove();
 
@@ -191,6 +192,26 @@ static int p2sb_read_from_cache(struct pci_bus *bus, unsigned int devfn,
 	return 0;
 }
 
+static int p2sb_read_from_dev(struct pci_bus *bus, unsigned int devfn,
+			      struct resource *mem)
+{
+	struct pci_dev *pdev;
+	int ret = 0;
+
+	pdev = pci_get_slot(bus, devfn);
+	if (!pdev)
+		return -ENODEV;
+
+	if (p2sb_valid_resource(pci_resource_n(pdev, 0)))
+		p2sb_read_bar0(pdev, mem);
+	else
+		ret = -ENOENT;
+
+	pci_dev_put(pdev);
+
+	return ret;
+}
+
 /**
  * p2sb_bar - Get Primary to Sideband (P2SB) bridge device BAR
  * @bus: PCI bus to communicate with
@@ -214,7 +235,10 @@ int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
 	if (!devfn)
 		p2sb_get_devfn(&devfn);
 
-	return p2sb_read_from_cache(bus, devfn, mem);
+	if (p2sb_hidden_by_bios)
+		return p2sb_read_from_cache(bus, devfn, mem);
+
+	return p2sb_read_from_dev(bus, devfn, mem);
 }
 EXPORT_SYMBOL_GPL(p2sb_bar);