drm/rockchip: psr: Sanitize semantics of allow/inhibit API

Currently both rockchip_drm_psr_activate() and _deactivate() only set the
boolean "active" flag without actually making sure that hardware state
complies with it.

Since we are going to extend the usage of this API to properly lock PSR
for the duration of atomic commits, we change the semantics in following
way:
 - a counter is used to track the number of inhibit requests,
 - PSR is actually disabled in hardware on first inhibit request,
 - PSR enable work is scheduled on last allow request.

The above allows using the API as a way to deterministically synchronize
PSR state changes with other DRM events, i.e. atomic commits and cursor
updates. As a nice side effect, the naming is sorted out and we have
"inhibit" for stopping the software logic and "enable" for hardware
state.

Signed-off-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180423105003.9004-26-enric.balletbo@collabora.com

drivers/gpu/drm/rockchip/analogix_dp-rockchip.c

@@ -134,7 +134,7 @@ static int rockchip_dp_poweron_end(struct analogix_dp_plat_data *plat_data)
 {
 	struct rockchip_dp_device *dp = to_dp(plat_data);
 
-	return rockchip_drm_psr_activate(&dp->encoder);
+	return rockchip_drm_psr_inhibit_put(&dp->encoder);
 }
 
 static int rockchip_dp_powerdown(struct analogix_dp_plat_data *plat_data)
@@ -142,7 +142,7 @@ static int rockchip_dp_powerdown(struct analogix_dp_plat_data *plat_data)
 	struct rockchip_dp_device *dp = to_dp(plat_data);
 	int ret;
 
-	ret = rockchip_drm_psr_deactivate(&dp->encoder);
+	ret = rockchip_drm_psr_inhibit_get(&dp->encoder);
 	if (ret != 0)
 		return ret;
 

drivers/gpu/drm/rockchip/rockchip_drm_psr.c

@@ -25,7 +25,7 @@ struct psr_drv {
 	struct drm_encoder	*encoder;
 
 	struct mutex		lock;
-	bool			active;
+	int			inhibit_count;
 	bool			enabled;
 
 	struct delayed_work	flush_work;
@@ -71,7 +71,7 @@ static int psr_set_state_locked(struct psr_drv *psr, bool enable)
 {
 	int ret;
 
-	if (!psr->active)
+	if (psr->inhibit_count > 0)
 		return -EINVAL;
 
 	if (enable == psr->enabled)
@@ -96,13 +96,18 @@ static void psr_flush_handler(struct work_struct *work)
 }
 
 /**
- * rockchip_drm_psr_activate - activate PSR on the given pipe
+ * rockchip_drm_psr_inhibit_put - release PSR inhibit on given encoder
  * @encoder: encoder to obtain the PSR encoder
  *
+ * Decrements PSR inhibit count on given encoder. Should be called only
+ * for a PSR inhibit count increment done before. If PSR inhibit counter
+ * reaches zero, PSR flush work is scheduled to make the hardware enter
+ * PSR mode in PSR_FLUSH_TIMEOUT_MS.
+ *
  * Returns:
  * Zero on success, negative errno on failure.
  */
-int rockchip_drm_psr_activate(struct drm_encoder *encoder)
+int rockchip_drm_psr_inhibit_put(struct drm_encoder *encoder)
 {
 	struct psr_drv *psr = find_psr_by_encoder(encoder);
 
@@ -110,21 +115,30 @@ int rockchip_drm_psr_activate(struct drm_encoder *encoder)
 		return PTR_ERR(psr);
 
 	mutex_lock(&psr->lock);
-	psr->active = true;
+	--psr->inhibit_count;
+	WARN_ON(psr->inhibit_count < 0);
+	if (!psr->inhibit_count)
+		mod_delayed_work(system_wq, &psr->flush_work,
+				 PSR_FLUSH_TIMEOUT_MS);
 	mutex_unlock(&psr->lock);
 
 	return 0;
 }
-EXPORT_SYMBOL(rockchip_drm_psr_activate);
+EXPORT_SYMBOL(rockchip_drm_psr_inhibit_put);
 
 /**
- * rockchip_drm_psr_deactivate - deactivate PSR on the given pipe
+ * rockchip_drm_psr_inhibit_get - acquire PSR inhibit on given encoder
  * @encoder: encoder to obtain the PSR encoder
  *
+ * Increments PSR inhibit count on given encoder. This function guarantees
+ * that after it returns PSR is turned off on given encoder and no PSR-related
+ * hardware state change occurs at least until a matching call to
+ * rockchip_drm_psr_inhibit_put() is done.
+ *
  * Returns:
  * Zero on success, negative errno on failure.
  */
-int rockchip_drm_psr_deactivate(struct drm_encoder *encoder)
+int rockchip_drm_psr_inhibit_get(struct drm_encoder *encoder)
 {
 	struct psr_drv *psr = find_psr_by_encoder(encoder);
 
@@ -132,14 +146,14 @@ int rockchip_drm_psr_deactivate(struct drm_encoder *encoder)
 		return PTR_ERR(psr);
 
 	mutex_lock(&psr->lock);
-	psr->active = false;
-	psr->enabled = false;
+	psr_set_state_locked(psr, false);
+	++psr->inhibit_count;
 	mutex_unlock(&psr->lock);
 	cancel_delayed_work_sync(&psr->flush_work);
 
 	return 0;
 }
-EXPORT_SYMBOL(rockchip_drm_psr_deactivate);
+EXPORT_SYMBOL(rockchip_drm_psr_inhibit_get);
 
 static void rockchip_drm_do_flush(struct psr_drv *psr)
 {
@@ -199,6 +213,11 @@ EXPORT_SYMBOL(rockchip_drm_psr_flush_all);
  * @encoder: encoder that obtain the PSR function
  * @psr_set: call back to set PSR state
  *
+ * The function returns with PSR inhibit counter initialized with one
+ * and the caller (typically encoder driver) needs to call
+ * rockchip_drm_psr_inhibit_put() when it becomes ready to accept PSR
+ * enable request.
+ *
  * Returns:
  * Zero on success, negative errno on failure.
  */
@@ -218,7 +237,7 @@ int rockchip_drm_psr_register(struct drm_encoder *encoder,
 	INIT_DELAYED_WORK(&psr->flush_work, psr_flush_handler);
 	mutex_init(&psr->lock);
 
-	psr->active = false;
+	psr->inhibit_count = 1;
 	psr->enabled = false;
 	psr->encoder = encoder;
 	psr->set = psr_set;
@@ -236,6 +255,11 @@ EXPORT_SYMBOL(rockchip_drm_psr_register);
  * @encoder: encoder that obtain the PSR function
  * @psr_set: call back to set PSR state
  *
+ * It is expected that the PSR inhibit counter is 1 when this function is
+ * called, which corresponds to a state when related encoder has been
+ * disconnected from any CRTCs and its driver called
+ * rockchip_drm_psr_inhibit_get() to stop the PSR logic.
+ *
  * Returns:
  * Zero on success, negative errno on failure.
  */
@@ -247,7 +271,12 @@ void rockchip_drm_psr_unregister(struct drm_encoder *encoder)
 	mutex_lock(&drm_drv->psr_list_lock);
 	list_for_each_entry_safe(psr, n, &drm_drv->psr_list, list) {
 		if (psr->encoder == encoder) {
-			cancel_delayed_work_sync(&psr->flush_work);
+			/*
+			 * Any other value would mean that the encoder
+			 * is still in use.
+			 */
+			WARN_ON(psr->inhibit_count != 1);
+
 			list_del(&psr->list);
 			kfree(psr);
 		}

drivers/gpu/drm/rockchip/rockchip_drm_psr.h

@@ -18,8 +18,8 @@
 void rockchip_drm_psr_flush_all(struct drm_device *dev);
 int rockchip_drm_psr_flush(struct drm_crtc *crtc);
 
-int rockchip_drm_psr_activate(struct drm_encoder *encoder);
-int rockchip_drm_psr_deactivate(struct drm_encoder *encoder);
+int rockchip_drm_psr_inhibit_put(struct drm_encoder *encoder);
+int rockchip_drm_psr_inhibit_get(struct drm_encoder *encoder);
 
 int rockchip_drm_psr_register(struct drm_encoder *encoder,
 			int (*psr_set)(struct drm_encoder *, bool enable));