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 5913320eb0b3 ("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 5913320eb0b3 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: 5913320eb0b3 ("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>

diff --git a/drivers/platform/x86/p2sb.c b/drivers/platform/x86/p2sb.c
index 46c108bbcbbac558597b8ba0de695c0928bf3543..cbbb0f809704eaa0210e6488b6a4f65bba4b9842 100644 (file)
--- a/drivers/platform/x86/p2sb.c
+++ b/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);