drm/sun4i: add lvds mode_valid function

mode_valid function is missing for lvds.

Add it making it pointed by encoder helper functions.
Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1520940019-68977-1-git-send-email-giulio.benetti@micronovasrl.com

drivers/gpu/drm/sun4i/sun4i_lvds.c

@@ -94,9 +94,64 @@ static void sun4i_lvds_encoder_disable(struct drm_encoder *encoder)
 	}
 }
 
+static enum drm_mode_status sun4i_lvds_encoder_mode_valid(struct drm_encoder *crtc,
+							  const struct drm_display_mode *mode)
+{
+	struct sun4i_lvds *lvds = drm_encoder_to_sun4i_lvds(crtc);
+	struct sun4i_tcon *tcon = lvds->tcon;
+	u32 hsync = mode->hsync_end - mode->hsync_start;
+	u32 vsync = mode->vsync_end - mode->vsync_start;
+	unsigned long rate = mode->clock * 1000;
+	long rounded_rate;
+
+	DRM_DEBUG_DRIVER("Validating modes...\n");
+
+	if (hsync < 1)
+		return MODE_HSYNC_NARROW;
+
+	if (hsync > 0x3ff)
+		return MODE_HSYNC_WIDE;
+
+	if ((mode->hdisplay < 1) || (mode->htotal < 1))
+		return MODE_H_ILLEGAL;
+
+	if ((mode->hdisplay > 0x7ff) || (mode->htotal > 0xfff))
+		return MODE_BAD_HVALUE;
+
+	DRM_DEBUG_DRIVER("Horizontal parameters OK\n");
+
+	if (vsync < 1)
+		return MODE_VSYNC_NARROW;
+
+	if (vsync > 0x3ff)
+		return MODE_VSYNC_WIDE;
+
+	if ((mode->vdisplay < 1) || (mode->vtotal < 1))
+		return MODE_V_ILLEGAL;
+
+	if ((mode->vdisplay > 0x7ff) || (mode->vtotal > 0xfff))
+		return MODE_BAD_VVALUE;
+
+	DRM_DEBUG_DRIVER("Vertical parameters OK\n");
+
+	tcon->dclk_min_div = 7;
+	tcon->dclk_max_div = 7;
+	rounded_rate = clk_round_rate(tcon->dclk, rate);
+	if (rounded_rate < rate)
+		return MODE_CLOCK_LOW;
+
+	if (rounded_rate > rate)
+		return MODE_CLOCK_HIGH;
+
+	DRM_DEBUG_DRIVER("Clock rate OK\n");
+
+	return MODE_OK;
+}
+
 static const struct drm_encoder_helper_funcs sun4i_lvds_enc_helper_funcs = {
 	.disable	= sun4i_lvds_encoder_disable,
 	.enable		= sun4i_lvds_encoder_enable,
+	.mode_valid	= sun4i_lvds_encoder_mode_valid,
 };
 
 static const struct drm_encoder_funcs sun4i_lvds_enc_funcs = {