[PATCH 2/4] drm/v3d: Flush MMU TLB and cache during runtime resume

[Maíra Canal <mcanal@igalia.com>]

v3d_mmu_set_page_table() ends by calling v3d_mmu_flush_all() to flush the
MMU cache and clear the TLB after reprogramming V3D_MMU_PT_PA_BASE.
v3d_mmu_flush_all() is gated by pm_runtime_get_if_active(), which returns
0 unless runtime_status == RPM_ACTIVE.

v3d_mmu_set_page_table() is called from two paths that *know* V3D is
reachable, but where the runtime PM status might be wrong:

  1. v3d_power_resume(): the runtime resume callback itself, where
     runtime_status is RPM_RESUMING.

  2. v3d_reset(): called from the DRM scheduler timeout handler with the
     hung job's pm_runtime reference held, so RPM_ACTIVE, but here we
     don't need to take an extra reference for the duration of the flush
     either.

In the first case pm_runtime_get_if_active() returns 0, the flush is
silently skipped, and V3D resumes executing with whatever MMUC/TLB state
happened to survive the last reset. This can leave stale translations
live across runtime PM cycles, manifesting as random GPU hangs.

Split the actual flush sequence into a helper that does the writes
unconditionally, and have v3d_mmu_set_page_table() call it directly.

Fixes: 458f2a712ab4 ("drm/v3d: Introduce Runtime Power Management")
Signed-off-by: Maíra Canal <mcanal@igalia.com>
---
 drivers/gpu/drm/v3d/v3d_mmu.c | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/v3d/v3d_mmu.c b/drivers/gpu/drm/v3d/v3d_mmu.c
index 630c64e51d2f..94f6676d5633 100644
--- a/drivers/gpu/drm/v3d/v3d_mmu.c
+++ b/drivers/gpu/drm/v3d/v3d_mmu.c
@@ -37,13 +37,14 @@ static bool v3d_mmu_is_aligned(u32 page, u32 page_address, size_t alignment)
 		IS_ALIGNED(page_address, alignment >> V3D_MMU_PAGE_SHIFT);
 }
 
-int v3d_mmu_flush_all(struct v3d_dev *v3d)
+/*
+ * Issue the MMUC flush and TLB clear unconditionally. The caller must
+ * already know that V3D is reachable. In particular, this is used from
+ * the runtime resume callback.
+ */
+static int v3d_mmu_flush_all_locked(struct v3d_dev *v3d)
 {
-	int ret = 0;
-
-	/* Flush the PTs only if we're already awake */
-	if (!pm_runtime_get_if_active(v3d->drm.dev))
-		return 0;
+	int ret;
 
 	V3D_WRITE(V3D_MMUC_CONTROL, V3D_MMUC_CONTROL_FLUSH |
 		  V3D_MMUC_CONTROL_ENABLE);
@@ -52,7 +53,7 @@ int v3d_mmu_flush_all(struct v3d_dev *v3d)
 			 V3D_MMUC_CONTROL_FLUSHING), 100);
 	if (ret) {
 		dev_err(v3d->drm.dev, "MMUC flush wait idle failed\n");
-		goto pm_put;
+		return ret;
 	}
 
 	V3D_WRITE(V3D_MMU_CTL, V3D_READ(V3D_MMU_CTL) |
@@ -63,7 +64,19 @@ int v3d_mmu_flush_all(struct v3d_dev *v3d)
 	if (ret)
 		dev_err(v3d->drm.dev, "MMU TLB clear wait idle failed\n");
 
-pm_put:
+	return ret;
+}
+
+int v3d_mmu_flush_all(struct v3d_dev *v3d)
+{
+	int ret;
+
+	/* Flush the PTs only if we're already awake */
+	if (!pm_runtime_get_if_active(v3d->drm.dev))
+		return 0;
+
+	ret = v3d_mmu_flush_all_locked(v3d);
+
 	v3d_pm_runtime_put(v3d);
 	return ret;
 }
@@ -85,7 +98,7 @@ int v3d_mmu_set_page_table(struct v3d_dev *v3d)
 		  V3D_MMU_ILLEGAL_ADDR_ENABLE);
 	V3D_WRITE(V3D_MMUC_CONTROL, V3D_MMUC_CONTROL_ENABLE);
 
-	return v3d_mmu_flush_all(v3d);
+	return v3d_mmu_flush_all_locked(v3d);
 }
 
 void v3d_mmu_insert_ptes(struct v3d_bo *bo)

-- 
2.54.0