drm: atmel-hlcdc: enable clock before configuring timing engine

[ Upstream commit 2c1fb9d ]

Changing pixel clock source without having this clock source enabled
will block the timing engine and the next operations after (in this case
setting ATMEL_HLCDC_CFG(5) settings in atmel_hlcdc_crtc_mode_set_nofb()
will fail). It is recomended (although in datasheet this is not present)
to actually enabled pixel clock source before doing any changes on timing
enginge (only SAM9X60 datasheet specifies that the peripheral clock and
pixel clock must be enabled before using LCD controller).

Fixes: 1a39678 ("drm: add Atmel HLCDC Display Controller support")
Signed-off-by: Claudiu Beznea <[email protected]>
Signed-off-by: Sam Ravnborg <[email protected]>
Cc: Boris Brezillon <[email protected]>
Cc: <[email protected]> # v4.0+
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Signed-off-by: Sasha Levin <[email protected]>

Author: claudiubeznea

drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c

@@ -81,7 +81,11 @@ static void atmel_hlcdc_crtc_mode_set_nofb(struct drm_crtc *c)
 	struct videomode vm;
 	unsigned long prate;
 	unsigned int cfg;
-	int div;
+	int div, ret;
+
+	ret = clk_prepare_enable(crtc->dc->hlcdc->sys_clk);
+	if (ret)
+		return;
 
 	vm.vfront_porch = adj->crtc_vsync_start - adj->crtc_vdisplay;
 	vm.vback_porch = adj->crtc_vtotal - adj->crtc_vsync_end;
@@ -140,6 +144,8 @@ static void atmel_hlcdc_crtc_mode_set_nofb(struct drm_crtc *c)
 			   ATMEL_HLCDC_VSPSU | ATMEL_HLCDC_VSPHO |
 			   ATMEL_HLCDC_GUARDTIME_MASK | ATMEL_HLCDC_MODE_MASK,
 			   cfg);
+
+	clk_disable_unprepare(crtc->dc->hlcdc->sys_clk);
 }
 
 static bool atmel_hlcdc_crtc_mode_fixup(struct drm_crtc *c,