drm/i915: make transcoder_name return a string

Nicer for eDP (actually "EDP" instead of "D"), and makes future
expansion for DSI transcoders easier.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/2ac55ed584e450fe154daecb6453dff8eede5e7d.1458070700.git.jani.nikula@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -125,7 +125,22 @@ enum transcoder {
 	TRANSCODER_EDP,
 	I915_MAX_TRANSCODERS
 };
-#define transcoder_name(t) ((t) + 'A')
+
+static inline const char *transcoder_name(enum transcoder transcoder)
+{
+	switch (transcoder) {
+	case TRANSCODER_A:
+		return "A";
+	case TRANSCODER_B:
+		return "B";
+	case TRANSCODER_C:
+		return "C";
+	case TRANSCODER_EDP:
+		return "EDP";
+	default:
+		return "<invalid>";
+	}
+}
 
 /*
  * I915_MAX_PLANES in the enum below is the maximum (across all platforms)

drivers/gpu/drm/i915/intel_display.c

@@ -12092,7 +12092,7 @@ static void intel_dump_pipe_config(struct intel_crtc *crtc,
 	DRM_DEBUG_KMS("[CRTC:%d]%s config %p for pipe %c\n", crtc->base.base.id,
 		      context, pipe_config, pipe_name(crtc->pipe));
 
-	DRM_DEBUG_KMS("cpu_transcoder: %c\n", transcoder_name(pipe_config->cpu_transcoder));
+	DRM_DEBUG_KMS("cpu_transcoder: %s\n", transcoder_name(pipe_config->cpu_transcoder));
 	DRM_DEBUG_KMS("pipe bpp: %i, dithering: %i\n",
 		      pipe_config->pipe_bpp, pipe_config->dither);
 	DRM_DEBUG_KMS("fdi/pch: %i, lanes: %i, gmch_m: %u, gmch_n: %u, link_m: %u, link_n: %u, tu: %u\n",
@@ -16221,7 +16221,7 @@ intel_display_print_error_state(struct drm_i915_error_state_buf *m,
 	}
 
 	for (i = 0; i < error->num_transcoders; i++) {
-		err_printf(m, "CPU transcoder: %c\n",
+		err_printf(m, "CPU transcoder: %s\n",
 			   transcoder_name(error->transcoder[i].cpu_transcoder));
 		err_printf(m, "  Power: %s\n",
 			   onoff(error->transcoder[i].power_domain_on));

drivers/gpu/drm/i915/intel_fifo_underrun.c

@@ -212,7 +212,7 @@ static void cpt_check_pch_fifo_underruns(struct intel_crtc *crtc)
 	I915_WRITE(SERR_INT, SERR_INT_TRANS_FIFO_UNDERRUN(pch_transcoder));
 	POSTING_READ(SERR_INT);
 
-	DRM_ERROR("pch fifo underrun on pch transcoder %c\n",
+	DRM_ERROR("pch fifo underrun on pch transcoder %s\n",
 		  transcoder_name(pch_transcoder));
 }
 
@@ -235,7 +235,7 @@ static void cpt_set_fifo_underrun_reporting(struct drm_device *dev,
 
 		if (old && I915_READ(SERR_INT) &
 		    SERR_INT_TRANS_FIFO_UNDERRUN(pch_transcoder)) {
-			DRM_ERROR("uncleared pch fifo underrun on pch transcoder %c\n",
+			DRM_ERROR("uncleared pch fifo underrun on pch transcoder %s\n",
 				  transcoder_name(pch_transcoder));
 		}
 	}
@@ -386,7 +386,7 @@ void intel_pch_fifo_underrun_irq_handler(struct drm_i915_private *dev_priv,
 {
 	if (intel_set_pch_fifo_underrun_reporting(dev_priv, pch_transcoder,
 						  false))
-		DRM_ERROR("PCH transcoder %c FIFO underrun\n",
+		DRM_ERROR("PCH transcoder %s FIFO underrun\n",
 			  transcoder_name(pch_transcoder));
 }