[RFC 1/3] drm: Add a way to iterate over minors

[Noralf Trønnes <noralf@xxxxxxxxxxx>]

This adds a way for in-kernel users to iterate over the available
DRM minors. The implementation is oops safe so the panic code
can safely use it.

Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
---
 drivers/gpu/drm/drm_drv.c | 30 ++++++++++++++++++++++++++++++
 include/drm/drmP.h        | 13 +++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index be27ed3..3b14366 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -292,6 +292,36 @@ void drm_minor_release(struct drm_minor *minor)
 }
 
 /**
+ * drm_minor_lookup - Lookup DRM minor
+ * @minor_id: Minor ID of the DRM-minor
+ *
+ * Looks up the given minor-ID and returns the respective DRM-minor object.
+ * No reference is taken on the underlying device.
+ * See drm_minor_for_each() for iterating over all minors.
+ *
+ * Returns:
+ * Pointer to minor-object or NULL.
+ */
+struct drm_minor *drm_minor_lookup(unsigned int minor_id)
+{
+	struct drm_minor *minor;
+	unsigned long flags;
+	int locked = 1;
+
+	if (oops_in_progress)
+		locked = spin_trylock_irqsave(&drm_minor_lock, flags);
+	else
+		spin_lock_irqsave(&drm_minor_lock, flags);
+
+	minor = idr_find(&drm_minors_idr, minor_id);
+
+	if (locked)
+		spin_unlock_irqrestore(&drm_minor_lock, flags);
+
+	return minor;
+}
+
+/**
  * DOC: driver instance overview
  *
  * A device instance for a drm driver is represented by struct &drm_device. This
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index d377865..bc7006e 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -974,6 +974,19 @@ void drm_dev_unregister(struct drm_device *dev);
 
 struct drm_minor *drm_minor_acquire(unsigned int minor_id);
 void drm_minor_release(struct drm_minor *minor);
+struct drm_minor *drm_minor_lookup(unsigned int minor_id);
+
+/**
+ * drm_minor_for_each - Iterate over DRM minors
+ * @minor: DRM minor handle
+ * @type: DRM minor type to iterate over
+ * @id: id handle
+ *
+ * Iterate over the registered DRM minors of a given type.
+ */
+#define drm_minor_for_each(minor, type, id)  \
+	for ((id) = 0; (id) < 64; (id)++)  \
+		if (((minor) = drm_minor_lookup((id) + (type) * 64)))
 
 /*@}*/
 
-- 
2.8.2

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