drm/sun4i: DW HDMI: Lower max. supported rate for H6

Currently resolutions with pixel clock higher than 340 MHz don't work
with H6 HDMI controller. They just produce a blank screen.

Limit maximum pixel clock rate to 340 MHz until scrambling is supported.

Cc: stable@vger.kernel.org # 5.0
Fixes: 40bb9d3147b2 ("drm/sun4i: Add support for H6 DW HDMI controller")
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190324190609.32721-1-jernej.skrabec@siol.net

1 files changed, 7 insertions, 2 deletions

diff --git a/drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c b/drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c
index dc47720c99ba..39d8509d96a0 100644
--- a/drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c
+++ b/drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c
@@ -48,8 +48,13 @@ static enum drm_mode_status
 sun8i_dw_hdmi_mode_valid_h6(struct drm_connector *connector,
                             const struct drm_display_mode *mode)
 {
-        /* This is max for HDMI 2.0b (4K@60Hz) */
-        if (mode->clock > 594000)
+        /*
+         * Controller support maximum of 594 MHz, which correlates to
+         * 4K@60Hz 4:4:4 or RGB. However, for frequencies greater than
+         * 340 MHz scrambling has to be enabled. Because scrambling is
+         * not yet implemented, just limit to 340 MHz for now.
+         */
+        if (mode->clock > 340000)
                 return MODE_CLOCK_HIGH;
 
         return MODE_OK;