drm/exynos: stop mixer before gating clocks during poweroff

Mixer should be power gated only after it is gracefully stopped.
The recommended sequence is to Stop the mixer and wait till
it enters to IDLE state before gating the clocks and power to
the mixer.

Signed-off-by: Rahul Sharma <[e-mail]>
Signed-off-by: Inki Dae <[e-mail]>

drivers/gpu/drm/exynos/exynos_mixer.c

···
 	mixer_regs_dump(ctx);
 }
 
+static void mixer_stop(struct mixer_context *ctx)
+{
+	struct mixer_resources *res = &ctx->mixer_res;
+	int timeout = 20;
+
+	mixer_reg_writemask(res, MXR_STATUS, 0, MXR_STATUS_REG_RUN);
+
+	while (!(mixer_reg_read(res, MXR_STATUS) & MXR_STATUS_REG_IDLE) &&
+			--timeout)
+		usleep_range(10000, 12000);
+
+	mixer_regs_dump(ctx);
+}
+
 static void vp_video_buffer(struct mixer_context *ctx, int win)
 {
 	struct mixer_resources *res = &ctx->mixer_res;
···
 	}
 	mutex_unlock(&ctx->mixer_mutex);
 
+	mixer_stop(ctx);
 	mixer_window_suspend(mgr);
 
 	ctx->int_en = mixer_reg_read(res, MXR_INT_EN);

drivers/gpu/drm/exynos/regs-mixer.h

···
 #define MXR_STATUS_BIG_ENDIAN		(1 << 3)
 #define MXR_STATUS_ENDIAN_MASK		(1 << 3)
 #define MXR_STATUS_SYNC_ENABLE		(1 << 2)
+#define MXR_STATUS_REG_IDLE		(1 << 1)
 #define MXR_STATUS_REG_RUN		(1 << 0)
 
 /* bits for MXR_CFG */