[PATCHv6 3/5] pci: No config access for disconnected devices

[Keith Busch <keith.busch@intel.com>]

If we've  detected the PCI device is disconnected, there is no need to
attempt to access its config space since we know the operation will
fail. This patch has all the config reads and writes return -ENODEV
error immediately when in such a state.

If a config read is sent to a disconnected device, the value will be
set to all 1's. This is the same as what hardware is expected to return
when accessing a removed device, but software can do this faster without
relying on hardware.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 drivers/pci/access.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/pci/access.c b/drivers/pci/access.c
index d37b2ed..d63e9dd 100644
--- a/drivers/pci/access.c
+++ b/drivers/pci/access.c
@@ -892,12 +892,20 @@ EXPORT_SYMBOL(pcie_capability_clear_and_set_dword);
 
 int pci_read_config_byte(const struct pci_dev *dev, int where, u8 *val)
 {
+	if (pci_dev_is_disconnected(dev)) {
+		*val = ~0;
+		return -ENODEV;
+	}
 	return pci_bus_read_config_byte(dev->bus, dev->devfn, where, val);
 }
 EXPORT_SYMBOL(pci_read_config_byte);
 
 int pci_read_config_word(const struct pci_dev *dev, int where, u16 *val)
 {
+	if (pci_dev_is_disconnected(dev)) {
+		*val = ~0;
+		return -ENODEV;
+	}
 	return pci_bus_read_config_word(dev->bus, dev->devfn, where, val);
 }
 EXPORT_SYMBOL(pci_read_config_word);
@@ -905,18 +913,26 @@ EXPORT_SYMBOL(pci_read_config_word);
 int pci_read_config_dword(const struct pci_dev *dev, int where,
 					u32 *val)
 {
+	if (pci_dev_is_disconnected(dev)) {
+		*val = ~0;
+		return -ENODEV;
+	}
 	return pci_bus_read_config_dword(dev->bus, dev->devfn, where, val);
 }
 EXPORT_SYMBOL(pci_read_config_dword);
 
 int pci_write_config_byte(const struct pci_dev *dev, int where, u8 val)
 {
+	if (pci_dev_is_disconnected(dev))
+		return -ENODEV;
 	return pci_bus_write_config_byte(dev->bus, dev->devfn, where, val);
 }
 EXPORT_SYMBOL(pci_write_config_byte);
 
 int pci_write_config_word(const struct pci_dev *dev, int where, u16 val)
 {
+	if (pci_dev_is_disconnected(dev))
+		return -ENODEV;
 	return pci_bus_write_config_word(dev->bus, dev->devfn, where, val);
 }
 EXPORT_SYMBOL(pci_write_config_word);
@@ -924,6 +940,8 @@ EXPORT_SYMBOL(pci_write_config_word);
 int pci_write_config_dword(const struct pci_dev *dev, int where,
 					 u32 val)
 {
+	if (pci_dev_is_disconnected(dev))
+		return -ENODEV;
 	return pci_bus_write_config_dword(dev->bus, dev->devfn, where, val);
 }
 EXPORT_SYMBOL(pci_write_config_dword);
-- 
2.7.2