drm/i915/dp: refactor aux_ch_name()

Convert aux_ch_name() to a helper that prints a string to a caller
provided buffer, and use it to get more consistent aux channel
debugs. Now that all users of aux_ch_name() are in intel_dp_aux.c, we
can make it static too.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230922105645.3991066-1-jani.nikula@intel.com

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

@@ -190,8 +190,6 @@ enum aux_ch {
 	AUX_CH_E_XELPD,
 };
 
-#define aux_ch_name(a) ((a) + 'A')
-
 enum phy {
 	PHY_NONE = -1,
 

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

@@ -14,6 +14,21 @@
 #include "intel_pps.h"
 #include "intel_tc.h"
 
+#define AUX_CH_NAME_BUFSIZE	6
+
+static const char *aux_ch_name(struct drm_i915_private *i915,
+			       char *buf, int size, enum aux_ch aux_ch)
+{
+	if (DISPLAY_VER(i915) >= 13 && aux_ch >= AUX_CH_D_XELPD)
+		snprintf(buf, size, "%c", 'A' + aux_ch - AUX_CH_D_XELPD + AUX_CH_D);
+	else if (DISPLAY_VER(i915) >= 12 && aux_ch >= AUX_CH_USBC1)
+		snprintf(buf, size, "USBC%c", '1' + aux_ch - AUX_CH_USBC1);
+	else
+		snprintf(buf, size, "%c", 'A' + aux_ch);
+
+	return buf;
+}
+
 u32 intel_dp_aux_pack(const u8 *src, int src_bytes)
 {
 	int i;
@@ -728,6 +743,7 @@ void intel_dp_aux_init(struct intel_dp *intel_dp)
 	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
 	struct intel_encoder *encoder = &dig_port->base;
 	enum aux_ch aux_ch = dig_port->aux_ch;
+	char buf[AUX_CH_NAME_BUFSIZE];
 
 	if (DISPLAY_VER(dev_priv) >= 14) {
 		intel_dp->aux_ch_ctl_reg = xelpdp_aux_ctl_reg;
@@ -764,17 +780,8 @@ void intel_dp_aux_init(struct intel_dp *intel_dp)
 	drm_dp_aux_init(&intel_dp->aux);
 
 	/* Failure to allocate our preferred name is not critical */
-	if (DISPLAY_VER(dev_priv) >= 13 && aux_ch >= AUX_CH_D_XELPD)
-		intel_dp->aux.name = kasprintf(GFP_KERNEL, "AUX %c/%s",
-					       aux_ch_name(aux_ch - AUX_CH_D_XELPD + AUX_CH_D),
-					       encoder->base.name);
-	else if (DISPLAY_VER(dev_priv) >= 12 && aux_ch >= AUX_CH_USBC1)
-		intel_dp->aux.name = kasprintf(GFP_KERNEL, "AUX USBC%c/%s",
-					       aux_ch - AUX_CH_USBC1 + '1',
-					       encoder->base.name);
-	else
-		intel_dp->aux.name = kasprintf(GFP_KERNEL, "AUX %c/%s",
-					       aux_ch_name(aux_ch),
+	intel_dp->aux.name = kasprintf(GFP_KERNEL, "AUX %s/%s",
+				       aux_ch_name(dev_priv, buf, sizeof(buf), aux_ch),
 				       encoder->base.name);
 
 	intel_dp->aux.transfer = intel_dp_aux_transfer;
@@ -819,6 +826,7 @@ enum aux_ch intel_dp_aux_ch(struct intel_encoder *encoder)
 	struct intel_encoder *other;
 	const char *source;
 	enum aux_ch aux_ch;
+	char buf[AUX_CH_NAME_BUFSIZE];
 
 	aux_ch = intel_bios_dp_aux_ch(encoder->devdata);
 	source = "VBT";
@@ -836,16 +844,17 @@ enum aux_ch intel_dp_aux_ch(struct intel_encoder *encoder)
 	other = get_encoder_by_aux_ch(encoder, aux_ch);
 	if (other) {
 		drm_dbg_kms(&i915->drm,
-			    "[ENCODER:%d:%s] AUX CH %c already claimed by [ENCODER:%d:%s]\n",
-			    encoder->base.base.id, encoder->base.name, aux_ch_name(aux_ch),
+			    "[ENCODER:%d:%s] AUX CH %s already claimed by [ENCODER:%d:%s]\n",
+			    encoder->base.base.id, encoder->base.name,
+			    aux_ch_name(i915, buf, sizeof(buf), aux_ch),
 			    other->base.base.id, other->base.name);
 		return AUX_CH_NONE;
 	}
 
 	drm_dbg_kms(&i915->drm,
-		    "[ENCODER:%d:%s] Using AUX CH %c (%s)\n",
+		    "[ENCODER:%d:%s] Using AUX CH %s (%s)\n",
 		    encoder->base.base.id, encoder->base.name,
-		    aux_ch_name(aux_ch), source);
+		    aux_ch_name(i915, buf, sizeof(buf), aux_ch), source);
 
 	return aux_ch;
 }