drm/i915: rework reading pipe disable fuses

This prepares to have possibly more than 3 pipes. I didn't want to
continue the previous approach since the check for "are the disabled
pipes the last ones" poses a combinatory explosion. We need that check
because in several places of the code we have that assumption. If that
ever becomes false in a new HW, other parts of the code would have to
change.

Now we start by considering we have info->num_pipes enabled and disable
each pipe that is marked as disabled. Then it's a simple matter of
checking if we have at least one pipe and that all the enabled ones are
the first pipes, i.e. there are no holes in the bitmask.

Cc: Jose Souza <jose.souza@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190625175437.14840-3-lucas.demarchi@intel.com

diff --git a/drivers/gpu/drm/i915/intel_device_info.c b/drivers/gpu/drm/i915/intel_device_info.c
index 7135d8d..e64536e 100644 (file)
--- a/drivers/gpu/drm/i915/intel_device_info.c
+++ b/drivers/gpu/drm/i915/intel_device_info.c
@@ -929,35 +929,25 @@ void intel_device_info_runtime_init(struct drm_i915_private *dev_priv)
                }
        } else if (HAS_DISPLAY(dev_priv) && INTEL_GEN(dev_priv) >= 9) {
                u32 dfsm = I915_READ(SKL_DFSM);
-               u8 disabled_mask = 0;
-               bool invalid;
-               int num_bits;
+               u8 enabled_mask = BIT(info->num_pipes) - 1;
 
                if (dfsm & SKL_DFSM_PIPE_A_DISABLE)
-                       disabled_mask |= BIT(PIPE_A);
+                       enabled_mask &= ~BIT(PIPE_A);
                if (dfsm & SKL_DFSM_PIPE_B_DISABLE)
-                       disabled_mask |= BIT(PIPE_B);
+                       enabled_mask &= ~BIT(PIPE_B);
                if (dfsm & SKL_DFSM_PIPE_C_DISABLE)
-                       disabled_mask |= BIT(PIPE_C);
-
-               num_bits = hweight8(disabled_mask);
-
-               switch (disabled_mask) {
-               case BIT(PIPE_A):
-               case BIT(PIPE_B):
-               case BIT(PIPE_A) | BIT(PIPE_B):
-               case BIT(PIPE_A) | BIT(PIPE_C):
-                       invalid = true;
-                       break;
-               default:
-                       invalid = false;
-               }
+                       enabled_mask &= ~BIT(PIPE_C);
 
-               if (num_bits > info->num_pipes || invalid)
-                       DRM_ERROR("invalid pipe fuse configuration: 0x%x\n",
-                                 disabled_mask);
+               /*
+                * At least one pipe should be enabled and if there are
+                * disabled pipes, they should be the last ones, with no holes
+                * in the mask.
+                */
+               if (enabled_mask == 0 || !is_power_of_2(enabled_mask + 1))
+                       DRM_ERROR("invalid pipe fuse configuration: enabled_mask=0x%x\n",
+                                 enabled_mask);
                else
-                       info->num_pipes -= num_bits;
+                       info->num_pipes = hweight8(enabled_mask);
        }
 
        /* Initialize slice/subslice/EU info */