linux-kernel - [PATCH] drm/sun4i: DW HDMI: Lower max. supported rate for H6

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Date:   Sun, 24 Mar 2019 20:06:09 +0100
From:   Jernej Skrabec <jernej.skrabec@...l.net>
To:     maxime.ripard@...tlin.com
Cc:     airlied@...ux.ie, daniel@...ll.ch, wens@...e.org,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: [PATCH] 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@...r.kernel.org # 5.0
Fixes: 40bb9d3147b2 ("drm/sun4i: Add support for H6 DW HDMI controller")
Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
---
 drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c | 9 +++++++--
 1 file 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 caea5a9f8f1d..ba4ce576b471 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@...z) */
-	if (mode->clock > 594000)
+	/*
+	 * Controller support maximum of 594 MHz, which correlates to
+	 * 4K@...z 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;
-- 
2.21.0