gpu: nvgpu: force idle if railgate not supported

Add a way to force idle and reset the GPU in case where GPU
rail gating is not supported
(i.e. platform->can_railgate = false)

In this case, we follow below sequence :
- once GPU is idle, get runtime reference which enables the clocks
- call prepare_poweroff() to save the state explicitly
- perform explicit reset assert/deassert
- call finalize_poweron() to restore the state
- drop the runtime reference taken earlier

Bug 1525284

Change-Id: Id5f3ec152093acd585631dfbf785d8e0561f9048
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/435620
GVS: Gerrit_Virtual_Submit
Reviewed-by: Arto Merilainen <amerilainen@nvidia.com>
Tested-by: Arto Merilainen <amerilainen@nvidia.com>

drivers/gpu/nvgpu/gk20a/gk20a.c

@@ -1743,9 +1743,6 @@ int gk20a_do_idle(void)
 	int ref_cnt;
 	bool is_railgated;
 
-	if (!platform->can_railgate)
-		return -ENOSYS;
-
 	/* acquire busy lock to block other busy() calls */
 	down_write(&g->busy_lock);
 
@@ -1772,10 +1769,14 @@ int gk20a_do_idle(void)
 
 	/*
 	 * if GPU is now idle, we will have only one ref count
-	 * drop this ref which will rail gate the GPU
+	 * drop this ref which will rail gate the GPU (if GPU
+	 * railgate is supported)
+	 * if GPU railgate is not supported then we need to
+	 * explicitly reset it
 	 */
 	pm_runtime_put_sync(&pdev->dev);
 
+	if (platform->can_railgate) {
 		/* add sufficient delay to allow GPU to rail gate */
 		msleep(platform->railgate_delay);
 
@@ -1791,6 +1792,16 @@ int gk20a_do_idle(void)
 			return 0;
 		else
 			goto fail_timeout;
+	} else {
+		pm_runtime_get_sync(&pdev->dev);
+		gk20a_pm_prepare_poweroff(&pdev->dev);
+
+		tegra_periph_reset_assert(platform->clk[0]);
+		udelay(10);
+
+		g->forced_reset = true;
+		return 0;
+	}
 
 fail:
 	pm_runtime_put_noidle(&pdev->dev);
@@ -1811,6 +1822,15 @@ int gk20a_do_unidle(void)
 	struct gk20a *g = get_gk20a(pdev);
 	struct gk20a_platform *platform = dev_get_drvdata(&pdev->dev);
 
+	if (g->forced_reset) {
+		tegra_periph_reset_deassert(platform->clk[0]);
+
+		gk20a_pm_finalize_poweron(&pdev->dev);
+		pm_runtime_put_sync(&pdev->dev);
+
+		g->forced_reset = false;
+	}
+
 	/* release the lock and open up all other busy() calls */
 	mutex_unlock(&platform->railgate_lock);
 	up_write(&g->busy_lock);

drivers/gpu/nvgpu/gk20a/gk20a.h

@@ -271,6 +271,7 @@ struct gk20a {
 	bool elpg_enabled;
 	bool aelpg_enabled;
 	bool forced_idle;
+	bool forced_reset;
 
 #ifdef CONFIG_DEBUG_FS
 	spinlock_t debugfs_lock;