[PATCH v4] gpu/drm: mediatek: call mtk_dsi_stop() after mtk_drm_crtc_atomic_disable()

[Hsin-Yi Wang]

mtk_dsi_stop() should be called after mtk_drm_crtc_atomic_disable(), which needs
ovl irq for drm_crtc_wait_one_vblank(), since after mtk_dsi_stop() is called,
ovl irq will be disabled. If drm_crtc_wait_one_vblank() is called after last
irq, it will timeout with this message: "vblank wait timed out on crtc 0". This
happens sometimes when turning off the screen.

In drm_atomic_helper.c#disable_outputs(),
the calling sequence when turning off the screen is:

1. mtk_dsi_encoder_disable()
     --> mtk_output_dsi_disable()
       --> mtk_dsi_stop();  // sometimes make vblank timeout in atomic_disable
       --> mtk_dsi_poweroff();
2. mtk_drm_crtc_atomic_disable()
     --> drm_crtc_wait_one_vblank();
     ...
       --> mtk_dsi_ddp_stop()
         --> mtk_dsi_poweroff();

mtk_dsi_poweroff() has reference count design, change to make mtk_dsi_stop()
called in mtk_dsi_poweroff() when refcount is 0.

Fixes: 0707632b5bac ("drm/mediatek: update DSI sub driver flow for sending commands to panel")
Signed-off-by: Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx>
---
change log v3->v4:
* add comment in code.
---
 drivers/gpu/drm/mediatek/mtk_dsi.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
index b00eb2d2e086..730594a91440 100644
--- a/drivers/gpu/drm/mediatek/mtk_dsi.c
+++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
@@ -630,6 +630,15 @@ static void mtk_dsi_poweroff(struct mtk_dsi *dsi)
 	if (--dsi->refcount != 0)
 		return;
 
+	/* 
+	 * mtk_dsi_stop() and mtk_dsi_start() is asymmetric, since
+	 * mtk_dsi_stop() should be called after mtk_drm_crtc_atomic_disable(),
+	 * which needs irq for vblank, and mtk_dsi_stop() will disable irq.
+	 * mtk_dsi_start() needs to be called in mtk_output_dsi_enable(),
+	 * after dsi is fully set.
+	 */
+	mtk_dsi_stop(dsi);
+
 	if (!mtk_dsi_switch_to_cmd_mode(dsi, VM_DONE_INT_FLAG, 500)) {
 		if (dsi->panel) {
 			if (drm_panel_unprepare(dsi->panel)) {
@@ -696,7 +705,6 @@ static void mtk_output_dsi_disable(struct mtk_dsi *dsi)
 		}
 	}
 
-	mtk_dsi_stop(dsi);
 	mtk_dsi_poweroff(dsi);
 
 	dsi->enabled = false;
-- 
2.20.1