drm/stm: ltdc: rework reset sequence

Reset must be properly assert before deassert.
This is important if there is an early boot splash screen
before the kernel start up.

Signed-off-by: Yannick Fertre <yannick.fertre@st.com>
Reviewed-by: Philippe Cornu <philippe.cornu@st.com>
Tested-by: Philippe Cornu <philippe.cornu@st.com>
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1530271355-5608-1-git-send-email-yannick.fertre@st.com

drivers/gpu/drm/stm/ltdc.c

@@ -1082,8 +1082,11 @@ int ltdc_load(struct drm_device *ddev)
 		}
 	}
 
-	if (!IS_ERR(rstc))
+	if (!IS_ERR(rstc)) {
+		reset_control_assert(rstc);
+		usleep_range(10, 20);
 		reset_control_deassert(rstc);
+	}
 
 	/* Disable interrupts */
 	reg_clear(ldev->regs, LTDC_IER,