[PATCH v4 2/5] drm/fb-helper: Add drm_fb_helper_set_suspend_lock()

[Noralf Trønnes]

This adds a function that also takes the console lock before calling
fb_set_suspend() in contrast to drm_fb_helper_set_suspend() which is
a plain wrapper around fb_set_suspend().
Resume is run asynchronously using a worker if the console lock is
already taken. This is modelled after the i915 driver.

Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
---
 drivers/gpu/drm/drm_fb_helper.c | 57 +++++++++++++++++++++++++++++++++++++++++
 include/drm/drm_fb_helper.h     |  9 +++++++
 2 files changed, 66 insertions(+)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index ce54e98..897e6f4 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -29,6 +29,7 @@
  */
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <linux/console.h>
 #include <linux/kernel.h>
 #include <linux/sysrq.h>
 #include <linux/slab.h>
@@ -618,6 +619,16 @@ static void drm_fb_helper_crtc_free(struct drm_fb_helper *helper)
 	kfree(helper->crtc_info);
 }
 
+static void drm_fb_helper_resume_worker(struct work_struct *work)
+{
+	struct drm_fb_helper *helper = container_of(work, struct drm_fb_helper,
+						    resume_work);
+
+	console_lock();
+	fb_set_suspend(helper->fbdev, 0);
+	console_unlock();
+}
+
 static void drm_fb_helper_dirty_work(struct work_struct *work)
 {
 	struct drm_fb_helper *helper = container_of(work, struct drm_fb_helper,
@@ -649,6 +660,7 @@ void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
 {
 	INIT_LIST_HEAD(&helper->kernel_fb_list);
 	spin_lock_init(&helper->dirty_lock);
+	INIT_WORK(&helper->resume_work, drm_fb_helper_resume_worker);
 	INIT_WORK(&helper->dirty_work, drm_fb_helper_dirty_work);
 	helper->dirty_clip.x1 = helper->dirty_clip.y1 = ~0;
 	helper->funcs = funcs;
@@ -1035,6 +1047,51 @@ void drm_fb_helper_set_suspend(struct drm_fb_helper *fb_helper, int state)
 }
 EXPORT_SYMBOL(drm_fb_helper_set_suspend);
 
+/**
+ * drm_fb_helper_set_suspend_lock - wrapper around fb_set_suspend that also
+ *                                  takes the console lock
+ * @fb_helper: driver-allocated fbdev helper
+ * @state: desired state, zero to resume, non-zero to suspend
+ *
+ * A wrapper around fb_set_suspend() that takes the console lock. If the lock
+ * isn't available on resume, a worker is tasked with waiting for the lock
+ * to become available. The console lock can be pretty contented on resume
+ * due to all the printk activity.
+ *
+ * This function can be called multiple times with the same state since
+ * &fb_info->state is checked to see if fbdev is running or not before locking.
+ *
+ * Use drm_fb_helper_set_suspend() if you need to take the lock yourself.
+ */
+void drm_fb_helper_set_suspend_lock(struct drm_fb_helper *fb_helper, int state)
+{
+	if (!fb_helper || !fb_helper->fbdev)
+		return;
+
+	/* make sure there's no pending/ongoing resume */
+	flush_work(&fb_helper->resume_work);
+
+	if (state) { /* suspend */
+		if (fb_helper->fbdev->state != FBINFO_STATE_RUNNING)
+			return;
+
+		console_lock();
+
+	} else { /* resume */
+		if (fb_helper->fbdev->state == FBINFO_STATE_RUNNING)
+			return;
+
+		if (!console_trylock()) {
+			schedule_work(&fb_helper->resume_work);
+			return;
+		}
+	}
+
+	fb_set_suspend(fb_helper->fbdev, state);
+	console_unlock();
+}
+EXPORT_SYMBOL(drm_fb_helper_set_suspend_lock);
+
 static int setcolreg(struct drm_crtc *crtc, u16 red, u16 green,
 		     u16 blue, u16 regno, struct fb_info *info)
 {
diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
index db8d478..db7e861 100644
--- a/include/drm/drm_fb_helper.h
+++ b/include/drm/drm_fb_helper.h
@@ -176,6 +176,7 @@ struct drm_fb_helper_connector {
  *              the screen buffer
  * @dirty_lock: spinlock protecting @dirty_clip
  * @dirty_work: worker used to flush the framebuffer
+ * @resume_work: worker used during resume if the console lock is already taken
  *
  * This is the main structure used by the fbdev helpers. Drivers supporting
  * fbdev emulation should embedded this into their overall driver structure.
@@ -196,6 +197,7 @@ struct drm_fb_helper {
 	struct drm_clip_rect dirty_clip;
 	spinlock_t dirty_lock;
 	struct work_struct dirty_work;
+	struct work_struct resume_work;
 
 	/**
 	 * @kernel_fb_list:
@@ -264,6 +266,8 @@ void drm_fb_helper_cfb_imageblit(struct fb_info *info,
 				 const struct fb_image *image);
 
 void drm_fb_helper_set_suspend(struct drm_fb_helper *fb_helper, int state);
+void drm_fb_helper_set_suspend_lock(struct drm_fb_helper *fb_helper,
+				    int state);
 
 int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info);
 
@@ -421,6 +425,11 @@ static inline void drm_fb_helper_set_suspend(struct drm_fb_helper *fb_helper,
 {
 }
 
+static inline void
+drm_fb_helper_set_suspend_lock(struct drm_fb_helper *fb_helper, int state)
+{
+}
+
 static inline int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
 {
 	return 0;
-- 
2.8.2