[Intel-gfx] [PATCH] drm/i915: Make sure cdclk is high enough for DP audio on VLV/CHV

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

On VLV/CHV there is some kind of linkage between the cdclk frequency
and the DP link frequency. The spec says:
"For DP audio configuration, cdclk frequency shall be set to
 meet the following requirements:
 DP Link Frequency(MHz) | Cdclk frequency(MHz)
 270                    | 320 or higher
 162                    | 200 or higher"

I suspect that would more accurately be expressed as
"cdclk >= DP link clock", and in any case we can express it like
that in the code because of the limited set of cdclk and link
frequencies we support.

Without this we can end up in a situation where the cdclk
is too low and enabling DP audio will kill the pipe. Happens
eg. with 2560x1440 modes where the 266MHz cdclk is sufficient
to pump the pixels (241.5 MHz dotclock) but is too low for
the DP audio due to the link frequency being 270 MHz.

Cc: stable at vger.kernel.org
Tested-by: Stefan Gottwald <gottwald at igel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111149
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/display/intel_cdclk.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
index d0581a1ac243..93b0d190c184 100644
--- a/drivers/gpu/drm/i915/display/intel_cdclk.c
+++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
@@ -2262,6 +2262,17 @@ int intel_crtc_compute_min_cdclk(const struct intel_crtc_state *crtc_state)
 	if (crtc_state->has_audio && INTEL_GEN(dev_priv) >= 9)
 		min_cdclk = max(2 * 96000, min_cdclk);
 
+	/*
+	 * "For DP audio configuration, cdclk frequency shall be set to
+	 *  meet the following requirements:
+	 *  DP Link Frequency(MHz) | Cdclk frequency(MHz)
+	 *  270                    | 320 or higher
+	 *  162                    | 200 or higher"
+	 */
+	if ((IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv)) &&
+	    intel_crtc_has_dp_encoder(crtc_state) && crtc_state->has_audio)
+		min_cdclk = max(crtc_state->port_clock, min_cdclk);
+
 	/*
 	 * On Valleyview some DSI panels lose (v|h)sync when the clock is lower
 	 * than 320000KHz.
-- 
2.21.0