[PATCH v2 06/34] drm/i915/dp_link_caps: Validate max link limits

[Imre Deak <imre.deak@intel.com>]

Add validation in intel_dp_link_caps_set_max_limits() to ensure that
the new maximum rate and lane count leave at least one allowed
configuration.

The validation takes disabled configurations and active forced
parameters into account. Disabled configurations are not supported yet,
so that part has no effect for now.

At the moment this validation is also performed by the link training
fallback code, but that will be removed later, leaving only the link
caps module to perform the validation added in this patch.

v2: Rebase on changes using a filter object instead of a mask of
    configuration indices.

Signed-off-by: Imre Deak <imre.deak@intel.com>
---
 .../gpu/drm/i915/display/intel_dp_link_caps.c | 28 ++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_caps.c b/drivers/gpu/drm/i915/display/intel_dp_link_caps.c
index 36895dd9d6c81..5976e85bb2729 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_caps.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_caps.c
@@ -558,6 +558,26 @@ void intel_dp_link_caps_get_max_limits(struct intel_dp_link_caps *link_caps,
 	*max_link_limits = link_caps->max_limits;
 }
 
+static bool max_link_limits_valid(struct intel_dp_link_caps *link_caps,
+				  const struct intel_dp_link_config *max_link_limits)
+{
+	struct intel_dp_link_caps_filter allowed_configs;
+	struct intel_dp_link_config forced_params;
+
+	if (max_link_limits->lane_count > INTEL_DP_MAX_LANE_COUNT ||
+	    !is_power_of_2(max_link_limits->lane_count))
+		return false;
+
+	/* TODO: Validate max_link_limits->rate against the source supported rates. */
+
+	intel_dp_link_caps_get_forced_params(link_caps, &forced_params);
+	/* TODO: Get filter for enabled configs. */
+	allowed_configs = calc_allowed_config_filter(link_caps, INTEL_DP_LINK_CAPS_FILTER_ALL,
+						     max_link_limits, &forced_params);
+
+	return allowed_configs.config_mask != 0;
+}
+
 /**
  * intel_dp_link_caps_set_max_limits - set the current maximum link limits
  * @link_caps: link capabilities state
@@ -566,6 +586,10 @@ void intel_dp_link_caps_get_max_limits(struct intel_dp_link_caps *link_caps,
  * Set the current maximum rate and lane count limits to @max_link_limits,
  * constraining the set of allowed configurations.
  *
+ * The new limits must leave at least one configuration allowed: the limits
+ * must not be below the currently active forced parameters or below all the
+ * configurations that remain after disabled configurations are excluded.
+ *
  * Unlike intel_dp_link_caps_get_max_limits(), the caller must serialize
  * this call against concurrent queries and updates to @link_caps, in line
  * with the rest of the API.
@@ -578,9 +602,11 @@ void intel_dp_link_caps_get_max_limits(struct intel_dp_link_caps *link_caps,
 bool intel_dp_link_caps_set_max_limits(struct intel_dp_link_caps *link_caps,
 				       const struct intel_dp_link_config *max_link_limits)
 {
+	if (!max_link_limits_valid(link_caps, max_link_limits))
+		return false;
+
 	set_max_link_limits_no_update(link_caps, max_link_limits);
 
-	/* TODO: validate max_link_limits */
 	return true;
 }
 
-- 
2.49.1