drm/i915: Get first crtc instead of PIPE_A crtc

intel_plane_fb_max_stride should return the max stride of
primary plane for first available pipe in intel device info
pipe_mask.
Similarly glk_force_audio_cdclk() should also use the first
available CRTC instead of pipe 'A' crtc to force the cdclk
changes.

changes since RFC:
- Introduced a helper to get first intel_crtc intel_get_first_crtc. [Ville]
v1:
- Used intel_get_first_crtc() instead of PIPE_A crtc in
  glk_force_audio_cdclk(). [Ville]

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200224124004.26712-6-anshuman.gupta@intel.com

drivers/gpu/drm/i915/display/intel_audio.c

@@ -844,7 +844,7 @@ static void glk_force_audio_cdclk(struct drm_i915_private *dev_priv,
 	struct intel_crtc *crtc;
 	int ret;
 
-	crtc = intel_get_crtc_for_pipe(dev_priv, PIPE_A);
+	crtc = intel_get_first_crtc(dev_priv);
 	if (!crtc)
 		return;
 

drivers/gpu/drm/i915/display/intel_display.c

@@ -2729,9 +2729,10 @@ u32 intel_plane_fb_max_stride(struct drm_i915_private *dev_priv,
 
 	/*
 	 * We assume the primary plane for pipe A has
-	 * the highest stride limits of them all.
+	 * the highest stride limits of them all,
+	 * if in case pipe A is disabled, use the first pipe from pipe_mask.
 	 */
-	crtc = intel_get_crtc_for_pipe(dev_priv, PIPE_A);
+	crtc = intel_get_first_crtc(dev_priv);
 	if (!crtc)
 		return 0;
 

drivers/gpu/drm/i915/display/intel_display_types.h

@@ -1406,6 +1406,12 @@ vlv_pipe_to_channel(enum pipe pipe)
 	}
 }
 
+static inline struct intel_crtc *
+intel_get_first_crtc(struct drm_i915_private *dev_priv)
+{
+	return to_intel_crtc(drm_crtc_from_index(&dev_priv->drm, 0));
+}
+
 static inline struct intel_crtc *
 intel_get_crtc_for_pipe(struct drm_i915_private *dev_priv, enum pipe pipe)
 {