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authorInaky Perez-Gonzalez <inaky@linux.intel.com>2006-11-22 23:40:31 +0300
committerGreg Kroah-Hartman <gregkh@suse.de>2006-12-02 01:36:59 +0300
commitbae94d02371c402408a4edfb95e71e88dbd3e973 (patch)
tree8886acf5950d8f95d5d4d5a9737c462035709914 /block
parent039d09a845209122c5193e650ab2d8b3c849ca7c (diff)
downloadlinux-bae94d02371c402408a4edfb95e71e88dbd3e973.tar.xz
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>
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