drm/imx: ipuv3-crtc: Allow to divide DI clock from TVEv2

This patch allows the IPU to divide the 27 MHz input clock from
the TVE by two to obtain the 13.5 MHz pixel clock needed for
NTSC/PAL SD modes.
Signed-off-by: NPhilipp Zabel <p.zabel@pengutronix.de>

drivers/gpu/drm/imx/ipuv3-crtc.c

@@ -161,13 +161,15 @@ static int ipu_crtc_mode_set(struct drm_crtc *crtc,
 		__func__, encoder_types);
 
 	/*
-	 * If we have DAC, TVDAC or LDB, then we need the IPU DI clock
-	 * to be the same as the LDB DI clock.
+	 * If we have DAC or LDB, then we need the IPU DI clock to be
+	 * the same as the LDB DI clock. For TVDAC, derive the IPU DI
+	 * clock from 27 MHz TVE_DI clock, but allow to divide it.
 	 */
 	if (encoder_types & (BIT(DRM_MODE_ENCODER_DAC) |
-			     BIT(DRM_MODE_ENCODER_TVDAC) |
 			     BIT(DRM_MODE_ENCODER_LVDS)))
 		sig_cfg.clkflags = IPU_DI_CLKMODE_SYNC | IPU_DI_CLKMODE_EXT;
+	else if (encoder_types & BIT(DRM_MODE_ENCODER_TVDAC))
+		sig_cfg.clkflags = IPU_DI_CLKMODE_EXT;
 	else
 		sig_cfg.clkflags = 0;