PCI: switch pci_{enable,disable}_device() to be nestable
Changes the pci_{enable,disable}_device() functions to work in a
nested basis, so that eg, three calls to enable_device() require three
calls to disable_device().
The reason for this is to simplify PCI drivers for
multi-interface/capability devices. These are devices that cram more
than one interface in a single function. A relevant example of that is
the Wireless [USB] Host Controller Interface (similar to EHCI) [see
http://www.intel.com/technology/comms/wusb/whci.htm].
In these kind of devices, multiple interfaces are accessed through a
single bar and IRQ line. For that, the drivers map only the smallest
area of the bar to access their register banks and use shared IRQ
handlers.
However, because the order at which those drivers load cannot be known
ahead of time, the sequence in which the calls to pci_enable_device()
and pci_disable_device() cannot be predicted. Thus:
1. driverA starts pci_enable_device()
2. driverB starts pci_enable_device()
3. driverA shutdown pci_disable_device()
4. driverB shutdown pci_disable_device()
between steps 3 and 4, driver B would loose access to it's device,
even if it didn't intend to.
By using this modification, the device won't be disabled until all the
callers to enable() have called disable().
This is implemented by replacing 'struct pci_dev->is_enabled' from a
bitfield to an atomic use count. Each caller to enable increments it,
each caller to disable decrements it. When the count increments from 0
to 1, __pci_enable_device() is called to actually enable the
device. When it drops to zero, pci_disable_device() actually does the
disabling.
We keep the backend __pci_enable_device() for pci_default_resume() to
use and also change the sysfs method implementation, so that userspace
enabling/disabling the device doesn't disable it one time too much.
Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 4279917..5a14b73 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -612,27 +612,48 @@
}
/**
+ * __pci_enable_device - Initialize device before it's used by a driver.
+ * @dev: PCI device to be initialized
+ *
+ * Initialize device before it's used by a driver. Ask low-level code
+ * to enable I/O and memory. Wake up the device if it was suspended.
+ * Beware, this function can fail.
+ *
+ * Note this function is a backend and is not supposed to be called by
+ * normal code, use pci_enable_device() instead.
+ */
+int
+__pci_enable_device(struct pci_dev *dev)
+{
+ int err;
+
+ err = pci_enable_device_bars(dev, (1 << PCI_NUM_RESOURCES) - 1);
+ if (err)
+ return err;
+ pci_fixup_device(pci_fixup_enable, dev);
+ return 0;
+}
+
+/**
* pci_enable_device - Initialize device before it's used by a driver.
* @dev: PCI device to be initialized
*
* Initialize device before it's used by a driver. Ask low-level code
* to enable I/O and memory. Wake up the device if it was suspended.
* Beware, this function can fail.
+ *
+ * Note we don't actually enable the device many times if we call
+ * this function repeatedly (we just increment the count).
*/
-int
-pci_enable_device(struct pci_dev *dev)
+int pci_enable_device(struct pci_dev *dev)
{
- int err;
-
- if (dev->is_enabled)
- return 0;
-
- err = pci_enable_device_bars(dev, (1 << PCI_NUM_RESOURCES) - 1);
- if (err)
- return err;
- pci_fixup_device(pci_fixup_enable, dev);
- dev->is_enabled = 1;
- return 0;
+ int result;
+ if (atomic_add_return(1, &dev->enable_cnt) > 1)
+ return 0; /* already enabled */
+ result = __pci_enable_device(dev);
+ if (result < 0)
+ atomic_dec(&dev->enable_cnt);
+ return result;
}
/**
@@ -651,12 +672,18 @@
*
* Signal to the system that the PCI device is not in use by the system
* anymore. This only involves disabling PCI bus-mastering, if active.
+ *
+ * Note we don't actually disable the device until all callers of
+ * pci_device_enable() have called pci_device_disable().
*/
void
pci_disable_device(struct pci_dev *dev)
{
u16 pci_command;
+ if (atomic_sub_return(1, &dev->enable_cnt) != 0)
+ return;
+
if (dev->msi_enabled)
disable_msi_mode(dev, pci_find_capability(dev, PCI_CAP_ID_MSI),
PCI_CAP_ID_MSI);
@@ -672,7 +699,6 @@
dev->is_busmaster = 0;
pcibios_disable_device(dev);
- dev->is_enabled = 0;
}
/**