The DECON channels are not cleared properly as the windows aren't
shadow protected. When accompanied with an IOMMU, it pagefaults, and
the kernel panics.

Implement shadow protect/unprotect, along with a standalone update,
for channel clearing to properly take effect.

Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
---
 drivers/gpu/drm/exynos/exynos7_drm_decon.c | 55 +++++++++++++++++-------------
 1 file changed, 32 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/exynos/exynos7_drm_decon.c b/drivers/gpu/drm/exynos/exynos7_drm_decon.c
index 4e4ced50ff15..7f0985eb216e 100644
--- a/drivers/gpu/drm/exynos/exynos7_drm_decon.c
+++ b/drivers/gpu/drm/exynos/exynos7_drm_decon.c
@@ -81,6 +81,28 @@ static const enum drm_plane_type decon_win_types[WINDOWS_NR] = {
 	DRM_PLANE_TYPE_CURSOR,
 };
 
+/**
+ * decon_shadow_protect_win() - disable updating values from shadow registers at vsync
+ *
+ * @ctx: display and enhancement controller context
+ * @win: window to protect registers for
+ * @protect: 1 to protect (disable updates)
+ */
+static void decon_shadow_protect_win(struct decon_context *ctx,
+				     unsigned int win, bool protect)
+{
+	u32 bits, val;
+
+	bits = SHADOWCON_WINx_PROTECT(win);
+
+	val = readl(ctx->regs + SHADOWCON);
+	if (protect)
+		val |= bits;
+	else
+		val &= ~bits;
+	writel(val, ctx->regs + SHADOWCON);
+}
+
 static void decon_wait_for_vblank(struct decon_context *ctx)
 {
 	if (ctx->suspended)
@@ -101,18 +123,27 @@ static void decon_wait_for_vblank(struct decon_context *ctx)
 static void decon_clear_channels(struct decon_context *ctx)
 {
 	unsigned int win, ch_enabled = 0;
+	u32 val;
 
 	/* Check if any channel is enabled. */
 	for (win = 0; win < WINDOWS_NR; win++) {
-		u32 val = readl(ctx->regs + WINCON(win));
+		val = readl(ctx->regs + WINCON(win));
 
 		if (val & WINCONx_ENWIN) {
+			decon_shadow_protect_win(ctx, win, true);
+
 			val &= ~WINCONx_ENWIN;
 			writel(val, ctx->regs + WINCON(win));
 			ch_enabled = 1;
+
+			decon_shadow_protect_win(ctx, win, false);
 		}
 	}
 
+	val = readl(ctx->regs + DECON_UPDATE);
+	val |= DECON_UPDATE_STANDALONE_F;
+	writel(val, ctx->regs + DECON_UPDATE);
+
 	/* Wait for vsync, as disable channel takes effect at next vsync */
 	if (ch_enabled)
 		decon_wait_for_vblank(ctx);
@@ -340,28 +371,6 @@ static void decon_win_set_colkey(struct decon_context *ctx, unsigned int win)
 	writel(keycon1, ctx->regs + WKEYCON1_BASE(win));
 }
 
-/**
- * decon_shadow_protect_win() - disable updating values from shadow registers at vsync
- *
- * @ctx: display and enhancement controller context
- * @win: window to protect registers for
- * @protect: 1 to protect (disable updates)
- */
-static void decon_shadow_protect_win(struct decon_context *ctx,
-				     unsigned int win, bool protect)
-{
-	u32 bits, val;
-
-	bits = SHADOWCON_WINx_PROTECT(win);
-
-	val = readl(ctx->regs + SHADOWCON);
-	if (protect)
-		val |= bits;
-	else
-		val &= ~bits;
-	writel(val, ctx->regs + SHADOWCON);
-}
-
 static void decon_atomic_begin(struct exynos_drm_crtc *crtc)
 {
 	struct decon_context *ctx = crtc->ctx;

-- 
2.46.1