linux-kernel - [PATCH 5.0 067/117] drm/sun4i: DW HDMI: Lower max. supported rate for H6

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Date:   Mon, 15 Apr 2019 21:00:37 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jernej Skrabec <jernej.skrabec@...l.net>,
        Maxime Ripard <maxime.ripard@...tlin.com>
Subject: [PATCH 5.0 067/117] drm/sun4i: DW HDMI: Lower max. supported rate for H6

From: Jernej Skrabec <jernej.skrabec@...l.net>

commit cd9063757a227cf31ebf5391ccda2bf583b0806e upstream.

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>
Signed-off-by: Maxime Ripard <maxime.ripard@...tlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190324190609.32721-1-jernej.skrabec@siol.net
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- 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;