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



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
co-assigned, but the toolstack is expected to ensure this.

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
Changes in v2:
- defer creating sysfs node to late init.
---
 drivers/xen/xen-pciback/pci_stub.c |  125 +++++++++++++++++++++++++++++++++++-
 drivers/xen/xen-pciback/pciback.h  |    1 +
 2 files changed, 123 insertions(+), 3 deletions(-)

diff --git a/drivers/xen/xen-pciback/pci_stub.c 
b/drivers/xen/xen-pciback/pci_stub.c
index d57a173..5697c2a 100644
--- a/drivers/xen/xen-pciback/pci_stub.c
+++ b/drivers/xen/xen-pciback/pci_stub.c
@@ -17,6 +17,7 @@
 #include <linux/wait.h>
 #include <linux/sched.h>
 #include <linux/atomic.h>
+#include <linux/delay.h>
 #include <xen/events.h>
 #include <asm/xen/pci.h>
 #include <asm/xen/hypervisor.h>
@@ -63,6 +64,117 @@ 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;
+       u16 ctrl;
+       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;
+               pci_save_state(pdev);
+       }
+
+       pci_read_config_word(dev->bus->self, PCI_BRIDGE_CONTROL, &ctrl);
+       ctrl |= PCI_BRIDGE_CTL_BUS_RESET;
+       pci_write_config_word(dev->bus->self, PCI_BRIDGE_CONTROL, ctrl);
+       msleep(200);
+
+       ctrl &= ~PCI_BRIDGE_CTL_BUS_RESET;
+       pci_write_config_word(dev->bus->self, PCI_BRIDGE_CONTROL, ctrl);
+       msleep(200);
+
+       list_for_each_entry(pdev, &dev->bus->devices, bus_list)
+               pci_restore_state(pdev);
+
+       return 0;
+}
+
+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;
+       struct kernfs_node *reset_dirent;
+       int ret;
+
+       reset_dirent = sysfs_get_dirent(dev->kobj.sd, "reset");
+       if (reset_dirent) {
+               sysfs_put(reset_dirent);
+               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 +215,8 @@ 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 +393,7 @@ 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 +517,7 @@ 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 +526,10 @@ 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 +657,8 @@ 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


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