PCI: Add pci_clear_master() as opposite of pci_set_master()

During an online device reset it may be useful to disable bus-mastering.
pci_disable_device() does that, and far more besides, so is not suitable
for an online reset.

Add pci_clear_master() which does just this.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Reviewed-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 28 insertions, 11 deletions

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index c824dc8d617..f3fd55df67d 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1667,6 +1667,22 @@ int pci_request_regions_exclusive(struct pci_dev *pdev, const char *res_name)
                                         ((1 << 6) - 1), res_name);
 }
 
+static void __pci_set_master(struct pci_dev *dev, bool enable)
+{
+        u16 old_cmd, cmd;
+
+        pci_read_config_word(dev, PCI_COMMAND, &old_cmd);
+        if (enable)
+                cmd = old_cmd | PCI_COMMAND_MASTER;
+        else
+                cmd = old_cmd & ~PCI_COMMAND_MASTER;
+        if (cmd != old_cmd) {
+                dev_dbg(&dev->dev, "%s bus mastering\n",
+                        enable ? "enabling" : "disabling");
+                pci_write_config_word(dev, PCI_COMMAND, cmd);
+        }
+        dev->is_busmaster = enable;
+}
 
 /**
  * pci_set_master - enables bus-mastering for device dev
@@ -1675,21 +1691,21 @@ int pci_request_regions_exclusive(struct pci_dev *pdev, const char *res_name)
  * Enables bus-mastering on the device and calls pcibios_set_master()
  * to do the needed arch specific settings.
  */
-void
-pci_set_master(struct pci_dev *dev)
+void pci_set_master(struct pci_dev *dev)
 {
-        u16 cmd;
-
-        pci_read_config_word(dev, PCI_COMMAND, &cmd);
-        if (! (cmd & PCI_COMMAND_MASTER)) {
-                dev_dbg(&dev->dev, "enabling bus mastering\n");
-                cmd |= PCI_COMMAND_MASTER;
-                pci_write_config_word(dev, PCI_COMMAND, cmd);
-        }
-        dev->is_busmaster = 1;
+        __pci_set_master(dev, true);
         pcibios_set_master(dev);
 }
 
+/**
+ * pci_clear_master - disables bus-mastering for device dev
+ * @dev: the PCI device to disable
+ */
+void pci_clear_master(struct pci_dev *dev)
+{
+        __pci_set_master(dev, false);
+}
+
 #ifdef PCI_DISABLE_MWI
 int pci_set_mwi(struct pci_dev *dev)
 {
@@ -2346,6 +2362,7 @@ EXPORT_SYMBOL(pci_release_selected_regions);
 EXPORT_SYMBOL(pci_request_selected_regions);
 EXPORT_SYMBOL(pci_request_selected_regions_exclusive);
 EXPORT_SYMBOL(pci_set_master);
+EXPORT_SYMBOL(pci_clear_master);
 EXPORT_SYMBOL(pci_set_mwi);
 EXPORT_SYMBOL(pci_try_set_mwi);
 EXPORT_SYMBOL(pci_clear_mwi);