drm/i915: Allow disabling error capture

We currently capture the GPU state after we detect a hang. This is vital
for us to both triage and debug hangs in the wild (post-mortem
debugging). However, it comes at the cost of running some potentially
dangerous code (since it has to make very few assumption about the state
of the driver) that is quite resource intensive.

This patch introduces both a method to disable error capture at runtime
(for users who hit bugs at runtime and need a workaround) and to disable
error capture at compiletime (for realtime users who want to minimise
any possible latency, and never require error capture, saving ~30k of
code). The cost is that we now have to be wary of (and test!) a kconfig
flag and a module parameter. The effect of the module parameter is easy
to verify through code inspection and runtime testing, but a kconfig flag
needs regular compile checking.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Acked-by: Jani Nikula <jani.nikula@linux.intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch
Link: http://patchwork.freedesktop.org/patch/msgid/20161012090522.367-2-chris@chris-wilson.co.uk

1 files changed, 20 insertions, 5 deletions

diff --git a/drivers/gpu/drm/i915/i915_sysfs.c b/drivers/gpu/drm/i915/i915_sysfs.c
index 1012eeea1324..47590ab08d7e 100644
--- a/drivers/gpu/drm/i915/i915_sysfs.c
+++ b/drivers/gpu/drm/i915/i915_sysfs.c
@@ -514,6 +514,8 @@ static const struct attribute *vlv_attrs[] = {
 	NULL,
 };
 
+#if IS_ENABLED(CONFIG_DRM_I915_CAPTURE_ERROR)
+
 static ssize_t error_state_read(struct file *filp, struct kobject *kobj,
 				struct bin_attribute *attr, char *buf,
 				loff_t off, size_t count)
@@ -571,6 +573,21 @@ static struct bin_attribute error_state_attr = {
 	.write = error_state_write,
 };
 
+static void i915_setup_error_capture(struct device *kdev)
+{
+	if (sysfs_create_bin_file(&kdev->kobj, &error_state_attr))
+		DRM_ERROR("error_state sysfs setup failed\n");
+}
+
+static void i915_teardown_error_capture(struct device *kdev)
+{
+	sysfs_remove_bin_file(&kdev->kobj, &error_state_attr);
+}
+#else
+static void i915_setup_error_capture(struct device *kdev) {}
+static void i915_teardown_error_capture(struct device *kdev) {}
+#endif
+
 void i915_setup_sysfs(struct drm_i915_private *dev_priv)
 {
 	struct device *kdev = dev_priv->drm.primary->kdev;
@@ -617,17 +634,15 @@ void i915_setup_sysfs(struct drm_i915_private *dev_priv)
 	if (ret)
 		DRM_ERROR("RPS sysfs setup failed\n");
 
-	ret = sysfs_create_bin_file(&kdev->kobj,
-				    &error_state_attr);
-	if (ret)
-		DRM_ERROR("error_state sysfs setup failed\n");
+	i915_setup_error_capture(kdev);
 }
 
 void i915_teardown_sysfs(struct drm_i915_private *dev_priv)
 {
 	struct device *kdev = dev_priv->drm.primary->kdev;
 
-	sysfs_remove_bin_file(&kdev->kobj, &error_state_attr);
+	i915_teardown_error_capture(kdev);
+
 	if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
 		sysfs_remove_files(&kdev->kobj, vlv_attrs);
 	else