[PATCH 2/2] xen-pciback: provide a "reset" sysfs file to try harder at an SBR

[David Vrabel <david.vrabel@citrix.com>]

The standard implementation of pci_reset_function() does not try an
SBR if there are other sibling devices.  This is a common
configuration for multi-function devices (e.g., GPUs with a HDMI audio
device function).

If all the functions are co-assigned to the same domain at the same
time, then it is safe to perform an SBR to reset all functions at the
same time.

Add a "reset" sysfs file with the same interface as the standard one
(i.e., write 1 to reset) that will try an SBR if all sibling devices
are unbound or bound to pciback.

Note that this is weaker than the requirement for functions to be
simultaneously co-assigned, but the toolstack is expected to ensure
this.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
Changes in v3:
- probe for function reset
- use pci_reset_bus().

Changes in v2:
- defer creating sysfs node to late init.
---
 drivers/xen/xen-pciback/pci_stub.c |  107 +++++++++++++++++++++++++++++++++++-
 drivers/xen/xen-pciback/pciback.h  |    1 +
 2 files changed, 105 insertions(+), 3 deletions(-)

diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c
index d57a173..c7deceb 100644
--- a/drivers/xen/xen-pciback/pci_stub.c
+++ b/drivers/xen/xen-pciback/pci_stub.c
@@ -63,6 +63,100 @@ static LIST_HEAD(pcistub_devices);
 static int initialize_devices;
 static LIST_HEAD(seized_devices);
 
+/*
+ * pci_reset_function() will only work if there is a mechanism to
+ * reset that single function (e.g., FLR or a D-state transition).
+ * For PCI hardware that has two or more functions but no per-function
+ * reset, we can do a bus reset iff all the functions are co-assigned
+ * to the same domain.
+ *
+ * If a function has no per-function reset mechanism the 'reset' sysfs
+ * file that the toolstack uses to reset a function prior to assigning
+ * the device will be missing.  In this case, pciback adds its own
+ * which will try a bus reset.
+ *
+ * Note: pciback does not check for co-assigment before doing a bus
+ * reset, only that the devices are bound to pciback.  The toolstack
+ * is assumed to have done the right thing.
+ */
+static int __pcistub_reset_function(struct pci_dev *dev)
+{
+	struct pci_dev *pdev;
+	int ret;
+
+	ret = __pci_reset_function_locked(dev);
+	if (ret == 0)
+		return 0;
+
+	if (pci_is_root_bus(dev->bus) || dev->subordinate || !dev->bus->self)
+		return -ENOTTY;
+
+	list_for_each_entry(pdev, &dev->bus->devices, bus_list) {
+		if (pdev != dev && (!pdev->driver
+				    || strcmp(pdev->driver->name, "pciback")))
+			return -ENOTTY;
+	}
+
+	return pci_reset_bus(dev->bus);
+}
+
+static int pcistub_reset_function(struct pci_dev *dev)
+{
+	int ret;
+
+	device_lock(&dev->dev);
+	ret = __pcistub_reset_function(dev);
+	device_unlock(&dev->dev);
+
+	return ret;
+}
+
+static ssize_t pcistub_reset_store(struct device *dev,
+				   struct device_attribute *attr,
+				   const char *buf, size_t count)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+	unsigned long val;
+	ssize_t result = strict_strtoul(buf, 0, &val);
+
+	if (result < 0)
+		return result;
+
+	if (val != 1)
+		return -EINVAL;
+
+	result = pcistub_reset_function(pdev);
+	if (result < 0)
+		return result;
+	return count;
+}
+static DEVICE_ATTR(reset, 0200, NULL, pcistub_reset_store);
+
+static int pcistub_try_create_reset_file(struct pci_dev *pci)
+{
+	struct xen_pcibk_dev_data *dev_data = pci_get_drvdata(pci);
+	struct device *dev = &pci->dev;
+	int ret;
+
+	/* Already have a per-function reset? */
+	if (pci_probe_reset_function(pci) == 0)
+		return 0;
+
+	ret = device_create_file(dev, &dev_attr_reset);
+	if (ret < 0)
+		return ret;
+	dev_data->created_reset_file = true;
+	return 0;
+}
+
+static void pcistub_remove_reset_file(struct pci_dev *pci)
+{
+	struct xen_pcibk_dev_data *dev_data = pci_get_drvdata(pci);
+
+	if (dev_data && dev_data->created_reset_file)
+		device_remove_file(&pci->dev, &dev_attr_reset);
+}
+
 static struct pcistub_device *pcistub_device_alloc(struct pci_dev *dev)
 {
 	struct pcistub_device *psdev;
@@ -103,7 +197,8 @@ static void pcistub_device_release(struct kref *kref)
 	/* Call the reset function which does not take lock as this
 	 * is called from "unbind" which takes a device_lock mutex.
 	 */
-	__pci_reset_function_locked(dev);
+	__pcistub_reset_function(psdev->dev);
+
 	if (pci_load_and_free_saved_state(dev, &dev_data->pci_saved_state))
 		dev_dbg(&dev->dev, "Could not reload PCI state\n");
 	else
@@ -280,7 +375,7 @@ void pcistub_put_pci_dev(struct pci_dev *dev)
 	/* This is OK - we are running from workqueue context
 	 * and want to inhibit the user from fiddling with 'reset'
 	 */
-	pci_reset_function(dev);
+	pcistub_reset_function(dev);
 	pci_restore_state(dev);
 
 	/* This disables the device. */
@@ -404,7 +499,7 @@ static int pcistub_init_device(struct pci_dev *dev)
 		dev_err(&dev->dev, "Could not store PCI conf saved state!\n");
 	else {
 		dev_dbg(&dev->dev, "resetting (FLR, D3, etc) the device\n");
-		__pci_reset_function_locked(dev);
+		__pcistub_reset_function(dev);
 		pci_restore_state(dev);
 	}
 	/* Now disable the device (this also ensures some private device
@@ -413,6 +508,10 @@ static int pcistub_init_device(struct pci_dev *dev)
 	dev_dbg(&dev->dev, "reset device\n");
 	xen_pcibk_reset_device(dev);
 
+	err = pcistub_try_create_reset_file(dev);
+	if (err < 0)
+		goto config_release;
+
 	dev->dev_flags |= PCI_DEV_FLAGS_ASSIGNED;
 	return 0;
 
@@ -540,6 +639,8 @@ static void pcistub_remove(struct pci_dev *dev)
 
 	dev_dbg(&dev->dev, "removing\n");
 
+	pcistub_remove_reset_file(dev);
+
 	spin_lock_irqsave(&pcistub_devices_lock, flags);
 
 	xen_pcibk_config_quirk_release(dev);
diff --git a/drivers/xen/xen-pciback/pciback.h b/drivers/xen/xen-pciback/pciback.h
index f72af87..708ade9 100644
--- a/drivers/xen/xen-pciback/pciback.h
+++ b/drivers/xen/xen-pciback/pciback.h
@@ -42,6 +42,7 @@ struct xen_pcibk_device {
 struct xen_pcibk_dev_data {
 	struct list_head config_fields;
 	struct pci_saved_state *pci_saved_state;
+	bool created_reset_file;
 	unsigned int permissive:1;
 	unsigned int warned_on_write:1;
 	unsigned int enable_intx:1;
-- 
1.7.10.4