[PATCH 3.16 112/305] drm/i915: Don't leave old junk in ilk active watermarks on readout

3.16.37-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ville Syrjälä <redacted>

commit 7045c3689f148a0c95f42bae8ef3eb2829ac7de9 upstream.

When we read out the watermark state from the hardware we're supposed to
transfer that into the active watermarks, but currently we fail to any
part of the active watermarks that isn't explicitly written. Let's clear
it all upfront.

Looks like this has been like this since the beginning, when I added the
readout. No idea why I didn't clear it up.

Cc: Matt Roper <redacted>
Fixes: 243e6a44b9ca ("drm/i915: Init HSW watermark tracking in intel_modeset_setup_hw_state()")
Signed-off-by: Ville Syrjälä <redacted>
Reviewed-by: Matt Roper <redacted>
Signed-off-by: Matt Roper <redacted>
Link: http://patchwork.freedesktop.org/patch/msgid/1463151318-14719-2-git-send-email-ville.syrjala@linux.intel.com
(cherry picked from commit 15606534bf0a65d8a74a90fd57b8712d147dbca6)
Signed-off-by: Jani Nikula <redacted>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <redacted>
---
 drivers/gpu/drm/i915/intel_pm.c | 2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c

@@ -2751,6 +2751,8 @@ static void ilk_pipe_wm_get_hw_state(str
 	if (IS_HASWELL(dev) || IS_BROADWELL(dev))
 		hw->wm_linetime[pipe] = I915_READ(PIPE_WM_LINETIME(pipe));
 
+	memset(active, 0, sizeof(*active));
+
 	active->pipe_enabled = intel_crtc_active(crtc);
 
 	if (active->pipe_enabled) {