drm/xe/configfs: Block runtime attribute changes

Although it's possible to change the attributes in runtime, they have no
effect after the driver is already bound to the device. Check for that
and return -EBUSY in that case.

This should help users understand what's going on when the behavior is
not changing even if the value from the configfs is "right", but it got
to that state too late.

Reviewed-by: Riana Tauro <riana.tauro@intel.com>
Link: https://lore.kernel.org/r/20250826153210.3068808-2-lucas.demarchi@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>

diff --git a/drivers/gpu/drm/xe/xe_configfs.c b/drivers/gpu/drm/xe/xe_configfs.c
index 29a12d02443d9afcc90f634f7e5d0feb544ece57..1025d3979b066f7bfc29cc2ff9afe784b22360b2 100644 (file)
--- a/drivers/gpu/drm/xe/xe_configfs.c
+++ b/drivers/gpu/drm/xe/xe_configfs.c
@@ -75,6 +75,8 @@
  *
  *     # echo 1 > /sys/kernel/config/xe/0000:03:00.0/survivability_mode
  *
+ * This attribute can only be set before binding to the device.
+ *
  * Allowed engines:
  * ----------------
  *
@@ -99,6 +101,8 @@
  * available for migrations, but it's disabled. This is intended for debugging
  * purposes only.
  *
+ * This attribute can only be set before binding to the device.
+ *
  * PSMI
  * ----
  *
@@ -109,6 +113,8 @@
  *
  *     # echo 1 > /sys/kernel/config/xe/0000:03:00.0/enable_psmi
  *
+ * This attribute can only be set before binding to the device.
+ *
  * Remove devices
  * ==============
  *
@@ -169,6 +175,32 @@ static struct xe_config_device *to_xe_config_device(struct config_item *item)
        return &to_xe_config_group_device(item)->config;
 }
 
+static bool is_bound(struct xe_config_group_device *dev)
+{
+       unsigned int domain, bus, slot, function;
+       struct pci_dev *pdev;
+       const char *name;
+       bool ret;
+
+       lockdep_assert_held(&dev->lock);
+
+       name = dev->group.cg_item.ci_name;
+       if (sscanf(name, "%x:%x:%x.%x", &domain, &bus, &slot, &function) != 4)
+               return false;
+
+       pdev = pci_get_domain_bus_and_slot(domain, bus, PCI_DEVFN(slot, function));
+       if (!pdev)
+               return false;
+
+       ret = pci_get_drvdata(pdev);
+       pci_dev_put(pdev);
+
+       if (ret)
+               pci_dbg(pdev, "Already bound to driver\n");
+
+       return ret;
+}
+
 static ssize_t survivability_mode_show(struct config_item *item, char *page)
 {
        struct xe_config_device *dev = to_xe_config_device(item);
@@ -187,6 +219,9 @@ static ssize_t survivability_mode_store(struct config_item *item, const char *pa
                return ret;
 
        guard(mutex)(&dev->lock);
+       if (is_bound(dev))
+               return -EBUSY;
+
        dev->config.survivability_mode = survivability_mode;
 
        return len;
@@ -270,6 +305,9 @@ static ssize_t engines_allowed_store(struct config_item *item, const char *page,
        }
 
        guard(mutex)(&dev->lock);
+       if (is_bound(dev))
+               return -EBUSY;
+
        dev->config.engines_allowed = val;
 
        return len;
@@ -293,6 +331,9 @@ static ssize_t enable_psmi_store(struct config_item *item, const char *page, siz
                return ret;
 
        guard(mutex)(&dev->lock);
+       if (is_bound(dev))
+               return -EBUSY;
+
        dev->config.enable_psmi = val;
 
        return len;