drm/mediatek: add refcount for DPI power on/off

After the kernel 4.4, the DRM disable flow was changed, if DPI was
disableed before CRTC, it will cause warning message as following:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 1339 at ../../linux/linux-4.4.24-mtk/drivers/gpu/drm/drm_irq.c:1326 drm_wait_one_vblank+0x188/0x18c()
vblank wait timed out on crtc 0
Modules linked in: bridge mt8521p_ir_shim(O) i2c_eeprom(O) mtk_m4(O) fuse_ctrl(O) virtual_block(O) caamkeys(PO) chk(PO) amperctl(O) ledctl(O) apple_auth(PO) micctl(O) sensors(PO) lla(O) sdd(PO) ice40_fpga(O) psmon(O) event_queue(PO) utils(O) blackbox(O)
CPU: 0 PID: 1339 Comm: kworker/0:1 Tainted: P        W  O    4.4.24 #1
Hardware name: Mediatek Cortex-A7 (Device Tree)
Workqueue: events drm_mode_rmfb_work_fn
[<c001a710>] (unwind_backtrace) from [<c00151e4>] (show_stack+0x20/0x24)
[<c00151e4>] (show_stack) from [<c027961c>] (dump_stack+0x98/0xac)
[<c027961c>] (dump_stack) from [<c002ac54>] (warn_slowpath_common+0x94/0xc4)
[<c002ac54>] (warn_slowpath_common) from [<c002acc4>] (warn_slowpath_fmt+0x40/0x48)
[<c002acc4>] (warn_slowpath_fmt) from [<c03307ac>] (drm_wait_one_vblank+0x188/0x18c)
[<c03307ac>] (drm_wait_one_vblank) from [<c03307d8>] (drm_crtc_wait_one_vblank+0x28/0x2c)
[<c03307d8>] (drm_crtc_wait_one_vblank) from [<c034f48c>] (mtk_drm_crtc_disable+0x78/0x240)
[<c034f48c>] (mtk_drm_crtc_disable) from [<c03240d4>] (drm_atomic_helper_commit_modeset_disables+0x128/0x3b8)
[<c03240d4>] (drm_atomic_helper_commit_modeset_disables) from [<c0350a7c>] (mtk_atomic_complete+0x74/0xb4)
[<c0350a7c>] (mtk_atomic_complete) from [<c0350b24>] (mtk_atomic_commit+0x68/0x98)
[<c0350b24>] (mtk_atomic_commit) from [<c034ab48>] (drm_atomic_commit+0x54/0x74)
[<c034ab48>] (drm_atomic_commit) from [<c0325c4c>] (drm_atomic_helper_set_config+0x7c/0xa0)
[<c0325c4c>] (drm_atomic_helper_set_config) from [<c0338594>] (drm_mode_set_config_internal+0x68/0xe4)
[<c0338594>] (drm_mode_set_config_internal) from [<c033967c>] (drm_framebuffer_remove+0xe4/0x120)
[<c033967c>] (drm_framebuffer_remove) from [<c0339700>] (drm_mode_rmfb_work_fn+0x48/0x58)
[<c0339700>] (drm_mode_rmfb_work_fn) from [<c0043a38>] (process_one_work+0x154/0x50c)
[<c0043a38>] (process_one_work) from [<c0044074>] (worker_thread+0x284/0x568)
[<c0044074>] (worker_thread) from [<c0049dc4>] (kthread+0xec/0x104)
[<c0049dc4>] (kthread) from [<c0010678>] (ret_from_fork+0x14/0x3c)
---[ end trace 12ae5358e992abd5 ]---

so, we add refcount for DPI power on/off to protect the flow.
Signed-off-by: Bibby Hsieh <bibby.hsieh@mediatek.com>
Signed-off-by: chunhui dai <chunhui.dai@mediatek.com>
Signed-off-by: CK Hu <ck.hu@mediatek.com>

drivers/gpu/drm/mediatek/mtk_dpi.c

@@ -76,8 +76,7 @@ struct mtk_dpi {
 	enum mtk_dpi_out_yc_map yc_map;
 	enum mtk_dpi_out_bit_num bit_num;
 	enum mtk_dpi_out_channel_swap channel_swap;
-	bool power_sta;
-	u8 power_ctl;
+	int refcount;
 };
 
 static inline struct mtk_dpi *mtk_dpi_from_encoder(struct drm_encoder *e)
@@ -90,11 +89,6 @@ enum mtk_dpi_polarity {
 	MTK_DPI_POLARITY_FALLING,
 };
 
-enum mtk_dpi_power_ctl {
-	DPI_POWER_START = BIT(0),
-	DPI_POWER_ENABLE = BIT(1),
-};
-
 struct mtk_dpi_polarities {
 	enum mtk_dpi_polarity de_pol;
 	enum mtk_dpi_polarity ck_pol;
@@ -367,40 +361,30 @@ static void mtk_dpi_config_color_format(struct mtk_dpi *dpi,
 	}
 }
 
-static void mtk_dpi_power_off(struct mtk_dpi *dpi, enum mtk_dpi_power_ctl pctl)
+static void mtk_dpi_power_off(struct mtk_dpi *dpi)
 {
-	dpi->power_ctl &= ~pctl;
-
-	if ((dpi->power_ctl & DPI_POWER_START) ||
-	    (dpi->power_ctl & DPI_POWER_ENABLE))
+	if (WARN_ON(dpi->refcount == 0))
 		return;
 
-	if (!dpi->power_sta)
+	if (--dpi->refcount != 0)
 		return;
 
 	mtk_dpi_disable(dpi);
 	clk_disable_unprepare(dpi->pixel_clk);
 	clk_disable_unprepare(dpi->engine_clk);
-	dpi->power_sta = false;
 }
 
-static int mtk_dpi_power_on(struct mtk_dpi *dpi, enum mtk_dpi_power_ctl pctl)
+static int mtk_dpi_power_on(struct mtk_dpi *dpi)
 {
 	int ret;
 
-	dpi->power_ctl |= pctl;
-
-	if (!(dpi->power_ctl & DPI_POWER_START) &&
-	    !(dpi->power_ctl & DPI_POWER_ENABLE))
-		return 0;
-
-	if (dpi->power_sta)
+	if (++dpi->refcount != 1)
 		return 0;
 
 	ret = clk_prepare_enable(dpi->engine_clk);
 	if (ret) {
 		dev_err(dpi->dev, "Failed to enable engine clock: %d\n", ret);
-		goto err_eng;
+		goto err_refcount;
 	}
 
 	ret = clk_prepare_enable(dpi->pixel_clk);
@@ -410,13 +394,12 @@ static int mtk_dpi_power_on(struct mtk_dpi *dpi, enum mtk_dpi_power_ctl pctl)
 	}
 
 	mtk_dpi_enable(dpi);
-	dpi->power_sta = true;
 	return 0;
 
 err_pixel:
 	clk_disable_unprepare(dpi->engine_clk);
-err_eng:
-	dpi->power_ctl &= ~pctl;
+err_refcount:
+	dpi->refcount--;
 	return ret;
 }
 
@@ -552,14 +535,14 @@ static void mtk_dpi_encoder_disable(struct drm_encoder *encoder)
 {
 	struct mtk_dpi *dpi = mtk_dpi_from_encoder(encoder);
 
-	mtk_dpi_power_off(dpi, DPI_POWER_ENABLE);
+	mtk_dpi_power_off(dpi);
 }
 
 static void mtk_dpi_encoder_enable(struct drm_encoder *encoder)
 {
 	struct mtk_dpi *dpi = mtk_dpi_from_encoder(encoder);
 
-	mtk_dpi_power_on(dpi, DPI_POWER_ENABLE);
+	mtk_dpi_power_on(dpi);
 	mtk_dpi_set_display_mode(dpi, &dpi->mode);
 }
 
@@ -582,14 +565,14 @@ static void mtk_dpi_start(struct mtk_ddp_comp *comp)
 {
 	struct mtk_dpi *dpi = container_of(comp, struct mtk_dpi, ddp_comp);
 
-	mtk_dpi_power_on(dpi, DPI_POWER_START);
+	mtk_dpi_power_on(dpi);
 }
 
 static void mtk_dpi_stop(struct mtk_ddp_comp *comp)
 {
 	struct mtk_dpi *dpi = container_of(comp, struct mtk_dpi, ddp_comp);
 
-	mtk_dpi_power_off(dpi, DPI_POWER_START);
+	mtk_dpi_power_off(dpi);
 }
 
 static const struct mtk_ddp_comp_funcs mtk_dpi_funcs = {