drm/rockchip: inno_hdmi: Add basic mode validation

As per TRM this controller supports pixelclocks starting from 25 MHz. The
maximum supported pixelclocks are defined by the phy configurations we
have. Also it can't support modes that require doubled clocks. If the
variant has a phy reference clock we can additionally validate against VESA
DMT'srecommendations.
Signed-off-by: Alex Bee <knaerzche@gmail.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20231222174220.55249-26-knaerzche@gmail.com

drivers/gpu/drm/rockchip/inno_hdmi.c

@@ -25,6 +25,8 @@
 
 #include "inno_hdmi.h"
 
+#define INNO_HDMI_MIN_TMDS_CLOCK  25000000U
+
 struct inno_hdmi_phy_config {
 	unsigned long pixelclock;
 	u8 pre_emphasis;
@@ -496,6 +498,38 @@ static int inno_hdmi_setup(struct inno_hdmi *hdmi,
 	return 0;
 }
 
+static enum drm_mode_status inno_hdmi_display_mode_valid(struct inno_hdmi *hdmi,
+							 struct drm_display_mode *mode)
+{
+	unsigned long mpixelclk, max_tolerance;
+	long rounded_refclk;
+
+	/* No support for double-clock modes */
+	if (mode->flags & DRM_MODE_FLAG_DBLCLK)
+		return MODE_BAD;
+
+	mpixelclk = mode->clock * 1000;
+
+	if (mpixelclk < INNO_HDMI_MIN_TMDS_CLOCK)
+		return MODE_CLOCK_LOW;
+
+	if (inno_hdmi_find_phy_config(hdmi, mpixelclk) < 0)
+		return MODE_CLOCK_HIGH;
+
+	if (hdmi->refclk) {
+		rounded_refclk = clk_round_rate(hdmi->refclk, mpixelclk);
+		if (rounded_refclk < 0)
+			return MODE_BAD;
+
+		/* Vesa DMT standard mentions +/- 0.5% max tolerance */
+		max_tolerance = mpixelclk / 200;
+		if (abs_diff((unsigned long)rounded_refclk, mpixelclk) > max_tolerance)
+			return MODE_NOCLOCK;
+	}
+
+	return MODE_OK;
+}
+
 static void inno_hdmi_encoder_enable(struct drm_encoder *encoder,
 				     struct drm_atomic_state *state)
 {
@@ -528,6 +562,7 @@ inno_hdmi_encoder_atomic_check(struct drm_encoder *encoder,
 			       struct drm_connector_state *conn_state)
 {
 	struct rockchip_crtc_state *s = to_rockchip_crtc_state(crtc_state);
+	struct inno_hdmi *hdmi = encoder_to_inno_hdmi(encoder);
 	struct drm_display_mode *mode = &crtc_state->adjusted_mode;
 	u8 vic = drm_match_cea_mode(mode);
 	struct inno_hdmi_connector_state *inno_conn_state =
@@ -548,7 +583,8 @@ inno_hdmi_encoder_atomic_check(struct drm_encoder *encoder,
 	inno_conn_state->rgb_limited_range =
 		drm_default_rgb_quant_range(mode) == HDMI_QUANTIZATION_RANGE_LIMITED;
 
-	return 0;
+	return  inno_hdmi_display_mode_valid(hdmi,
+				&crtc_state->adjusted_mode) == MODE_OK ? 0 : -EINVAL;
 }
 
 static struct drm_encoder_helper_funcs inno_hdmi_encoder_helper_funcs = {
@@ -589,7 +625,9 @@ static enum drm_mode_status
 inno_hdmi_connector_mode_valid(struct drm_connector *connector,
 			       struct drm_display_mode *mode)
 {
-	return MODE_OK;
+	struct inno_hdmi *hdmi = connector_to_inno_hdmi(connector);
+
+	return  inno_hdmi_display_mode_valid(hdmi, mode);
 }
 
 static int