Patch "drm/i915/dp: BDW cdclk fix for DP audio" has been added to the 4.8-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    drm/i915/dp: BDW cdclk fix for DP audio

to the 4.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-i915-dp-bdw-cdclk-fix-for-dp-audio.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From fbb21c5202ae7f1e71e832b1af59fb047da6383e Mon Sep 17 00:00:00 2001
From: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Date: Tue, 1 Nov 2016 11:47:59 -0700
Subject: drm/i915/dp: BDW cdclk fix for DP audio
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>

commit fbb21c5202ae7f1e71e832b1af59fb047da6383e upstream.

According to BSpec, cdclk for BDW has to be not less than 432 MHz with DP
audio enabled, port width x4, and link rate HBR2 (5.4 GHz). With cdclk less
than 432 MHz, enabling audio leads to pipe FIFO underruns and displays
cycling on/off.

>From BSpec:
"Display» BDW-SKL» dpr» [Register] DP_TP_CTL [BDW+,EXCLUDE(CHV)]
Workaround : Do not use DisplayPort with CDCLK less than 432 MHz, audio
enabled, port width x4, and link rate HBR2 (5.4 GHz), or else there may
be audio corruption or screen corruption."

Since, some DP configurations (e.g., MST) use port width x4 and HBR2
link rate, let's increase the cdclk to >= 432 MHz to enable audio for those
cases.

v4: Changed commit message
v3: Combine BDW pixel rate adjustments into a function (Jani)
v2: Restrict fix to BDW
    Retain the set cdclk across modesets (Ville)
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1478026080-2925-1-git-send-email-dhinakaran.pandiyan@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(cherry picked from commit b30ce9e0552aa017ac6f2243f3c2d8e36fe52e69)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

---
 drivers/gpu/drm/i915/intel_display.c |   27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -9737,6 +9737,27 @@ static void bxt_modeset_commit_cdclk(str
 	bxt_set_cdclk(to_i915(dev), req_cdclk);
 }
 
+static int bdw_adjust_min_pipe_pixel_rate(struct intel_crtc_state *crtc_state,
+					  int pixel_rate)
+{
+	/* pixel rate mustn't exceed 95% of cdclk with IPS on BDW */
+	if (crtc_state->ips_enabled)
+		pixel_rate = DIV_ROUND_UP(pixel_rate * 100, 95);
+
+	/* BSpec says "Do not use DisplayPort with CDCLK less than
+	 * 432 MHz, audio enabled, port width x4, and link rate
+	 * HBR2 (5.4 GHz), or else there may be audio corruption or
+	 * screen corruption."
+	 */
+	if (intel_crtc_has_dp_encoder(crtc_state) &&
+	    crtc_state->has_audio &&
+	    crtc_state->port_clock >= 540000 &&
+	    crtc_state->lane_count == 4)
+		pixel_rate = max(432000, pixel_rate);
+
+	return pixel_rate;
+}
+
 /* compute the max rate for new configuration */
 static int ilk_max_pixel_rate(struct drm_atomic_state *state)
 {
@@ -9762,9 +9783,9 @@ static int ilk_max_pixel_rate(struct drm
 
 		pixel_rate = ilk_pipe_pixel_rate(crtc_state);
 
-		/* pixel rate mustn't exceed 95% of cdclk with IPS on BDW */
-		if (IS_BROADWELL(dev_priv) && crtc_state->ips_enabled)
-			pixel_rate = DIV_ROUND_UP(pixel_rate * 100, 95);
+		if (IS_BROADWELL(dev_priv))
+			pixel_rate = bdw_adjust_min_pipe_pixel_rate(crtc_state,
+								    pixel_rate);
 
 		intel_state->min_pixclk[i] = pixel_rate;
 	}


Patches currently in stable-queue which might be from dhinakaran.pandiyan@intel.com are

queue-4.8/drm-i915-dp-bdw-cdclk-fix-for-dp-audio.patch
queue-4.8/drm-i915-dp-extend-bdw-dp-audio-workaround-to-gen9-platforms.patch