device: Add helper function devfn_disable()

devfn_disable() function is used to disable a device based on
given bus, device function number. This function checks if the
device is at enable state and disables the device.

Change-Id: Ia4a8bfec7fc95c729a5bb156f88e9aab3bf5dd41
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55354
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>

src/device/device.c

@@ -21,6 +21,13 @@
 extern struct device *last_dev;
 /** Linked list of free resources */
 struct resource *free_resources = NULL;
+/* Disable a PCI device based on bus, device and function. */
+void devfn_disable(const struct bus *bus, unsigned int devfn)
+{
+	struct device *dev = pcidev_path_behind(bus, devfn);
+	if (dev)
+		dev->enabled = 0;
+}
 
 /**
  * Initialize all chips of statically known devices.

src/include/device/device.h

@@ -178,6 +178,8 @@ void dev_initialize(void);
 void dev_optimize(void);
 void dev_finalize(void);
 void dev_finalize_chips(void);
+/* Function used to override device state */
+void devfn_disable(const struct bus *bus, unsigned int devfn);
 
 /* Generic device helper functions */
 int reset_bus(struct bus *bus);