[Intel-gfx] [PATCH] drm/i915/display: Add missing checks for cdclk crawling

[Anusha Srivatsa <anusha.srivatsa@intel.com>]

cdclk_sanitize() function was written assuming vco was a signed integer.
vco gets assigned to -1 (essentially ~0) for the case where PLL
might be enabled and vco is not a frequency that will ever
get used. In such a scenario the right thing to do is disable the
PLL and re-enable it again with a valid frequency.
However the vco is declared as a unsigned variable.
With the above assumption, driver takes crawl path when not needed.
Add explicit check to not crawl in the case of an invalid PLL.

v2: Move the check from .h to .c (MattR)
- Move check to bxt_set_cdclk() instead of
intel_modeset_calc_cdclk() which is directly in
the path of the sanitize() function (Ville)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
---
 drivers/gpu/drm/i915/display/intel_cdclk.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
index 8a9031012d74..2d9b7ba58358 100644
--- a/drivers/gpu/drm/i915/display/intel_cdclk.c
+++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
@@ -1716,6 +1716,16 @@ static void dg2_cdclk_squash_program(struct drm_i915_private *i915,
 	intel_de_write(i915, CDCLK_SQUASH_CTL, squash_ctl);
 }
 
+static bool cdclk_pll_is_unknown(unsigned int vco)
+{
+	/*
+	 * Ensure driver does not take the crawl path for the
+	 * case when the vco is set to ~0 in the
+	 * sanitize path.
+	 */
+	return (vco == ~0);
+}
+
 static void bxt_set_cdclk(struct drm_i915_private *dev_priv,
 			  const struct intel_cdclk_config *cdclk_config,
 			  enum pipe pipe)
@@ -1748,7 +1758,8 @@ static void bxt_set_cdclk(struct drm_i915_private *dev_priv,
 		return;
 	}
 
-	if (HAS_CDCLK_CRAWL(dev_priv) && dev_priv->display.cdclk.hw.vco > 0 && vco > 0) {
+	if (HAS_CDCLK_CRAWL(dev_priv) && dev_priv->display.cdclk.hw.vco > 0 && vco > 0 &&
+	    (!cdclk_pll_is_unknown(dev_priv->display.cdclk.hw.vco))) {
 		if (dev_priv->display.cdclk.hw.vco != vco)
 			adlp_cdclk_pll_crawl(dev_priv, vco);
 	} else if (DISPLAY_VER(dev_priv) >= 11)
-- 
2.25.1