drm/i915/gen9: Fix PCODE polling during CDCLK change notification

commit 848496e5902833600f7992f4faa82dc1546051ba
Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
Date:   Wed Jul 13 16:32:03 2016 +0300

    drm/i915: Wait up to 3ms for the pcu to ack the cdclk change request on SKL

increased the timeout to match the spec, but we still see a timeout on
at least one SKL. A CDCLK change request following the failed one will
succeed nevertheless.

I could reproduce this problem easily by running kms_pipe_crc_basic in a
loop. In all failure cases _wait_for() was pre-empted for >3ms and so in
the worst case - when the pre-emption happened right after calculating
timeout__ in _wait_for() - we called skl_cdclk_wait_for_pcu_ready() only
once which failed and so _wait_for() timed out. As opposed to this the
spec says to keep retrying the request for at most a 3ms period.

To fix this send the first request explicitly to guarantee that there is
3ms between the first and last request. Though this matches the spec, I
noticed that in rare cases this can still time out if we sent only a few
requests (in the worst case 2) _and_ PCODE is busy for some reason even
after a previous request and a 3ms delay. To work around this retry the
polling with pre-emption disabled to maximize the number of requests.
Also increase the timeout to 10ms to account for interrupts that could
reduce the number of requests. With this change I couldn't trigger
the problem.

v2:
- Use 1ms poll period instead of 10us. (Chris)
v3:
- Poll with pre-emption disabled to increase the number of request
  attempts. (Ville, Chris)
- Factor out a helper to poll, it's also needed by the next patch.
v4:
- Pass reply_mask, reply to skl_pcode_request(), instead of assuming the
  reply is generic. (Ville)
v5:
- List the request specific timeout values as code comment. (Ville)
v6:
- Try the poll first with preemption enabled.
- Add code comment about first request being queued by PCODE. (Art)
- Add timeout_base_ms argument. (Ville)
v7:
- Clarify code comment about first queued request. (Chris)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Art Runyan <arthur.j.runyan@intel.com>
Cc: <stable@vger.kernel.org> # v4.2- : 3b2c171 : drm/i915: Wait up to 3ms
Cc: <stable@vger.kernel.org> # v4.2-
Fixes: 5d96d8afcfbb ("drm/i915/skl: Deinit/init the display at suspend/resume")
Reference: https://bugs.freedesktop.org/show_bug.cgi?id=97929
Testcase: igt/kms_pipe_crc_basic/suspend-read-crc-pipe-B
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1480955258-26311-1-git-send-email-imre.deak@intel.com
(cherry picked from commit a0b8a1fe34430c3a82258e8cb45f5968bdf31afd)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

1 files changed, 10 insertions, 21 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 4ef5a39acc69..7d234043822d 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -6244,35 +6244,24 @@ skl_dpll0_disable(struct drm_i915_private *dev_priv)
 	dev_priv->cdclk_pll.vco = 0;
 }
 
-static bool skl_cdclk_pcu_ready(struct drm_i915_private *dev_priv)
-{
-	int ret;
-	u32 val;
-
-	/* inform PCU we want to change CDCLK */
-	val = SKL_CDCLK_PREPARE_FOR_CHANGE;
-	mutex_lock(&dev_priv->rps.hw_lock);
-	ret = sandybridge_pcode_read(dev_priv, SKL_PCODE_CDCLK_CONTROL, &val);
-	mutex_unlock(&dev_priv->rps.hw_lock);
-
-	return ret == 0 && (val & SKL_CDCLK_READY_FOR_CHANGE);
-}
-
-static bool skl_cdclk_wait_for_pcu_ready(struct drm_i915_private *dev_priv)
-{
-	return _wait_for(skl_cdclk_pcu_ready(dev_priv), 3000, 10) == 0;
-}
-
 static void skl_set_cdclk(struct drm_i915_private *dev_priv, int cdclk, int vco)
 {
 	u32 freq_select, pcu_ack;
+	int ret;
 
 	WARN_ON((cdclk == 24000) != (vco == 0));
 
 	DRM_DEBUG_DRIVER("Changing CDCLK to %d kHz (VCO %d kHz)\n", cdclk, vco);
 
-	if (!skl_cdclk_wait_for_pcu_ready(dev_priv)) {
-		DRM_ERROR("failed to inform PCU about cdclk change\n");
+	mutex_lock(&dev_priv->rps.hw_lock);
+	ret = skl_pcode_request(dev_priv, SKL_PCODE_CDCLK_CONTROL,
+				SKL_CDCLK_PREPARE_FOR_CHANGE,
+				SKL_CDCLK_READY_FOR_CHANGE,
+				SKL_CDCLK_READY_FOR_CHANGE, 3);
+	mutex_unlock(&dev_priv->rps.hw_lock);
+	if (ret) {
+		DRM_ERROR("Failed to inform PCU about cdclk change (%d)\n",
+			  ret);
 		return;
 	}