drm/bridge: tc358767: Add support for address-only I2C transfers

Transfer size of zero means a request to do an address-only
transfer. Since the HW support this, we probably shouldn't be just
ignoring such requests. While at it allow DP_AUX_I2C_MOT flag to pass
through, since it is supported by the HW as well.
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Andrzej Hajda <a.hajda@samsung.com>
Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Andrey Gusakov <andrey.gusakov@cogentembedded.com>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Cory Tusar <cory.tusar@zii.aero>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190619052716.16831-16-andrew.smirnov@gmail.com

drivers/gpu/drm/bridge/tc358767.c

@@ -136,6 +136,8 @@
 
 /* AUX channel */
 #define DP0_AUXCFG0		0x0660
+#define DP0_AUXCFG0_BSIZE	GENMASK(11, 8)
+#define DP0_AUXCFG0_ADDR_ONLY	BIT(4)
 #define DP0_AUXCFG1		0x0664
 #define AUX_RX_FILTER_EN		BIT(16)
 
@@ -317,6 +319,18 @@ static int tc_aux_read_data(struct tc_data *tc, void *data, size_t size)
 	return size;
 }
 
+static u32 tc_auxcfg0(struct drm_dp_aux_msg *msg, size_t size)
+{
+	u32 auxcfg0 = msg->request;
+
+	if (size)
+		auxcfg0 |= FIELD_PREP(DP0_AUXCFG0_BSIZE, size - 1);
+	else
+		auxcfg0 |= DP0_AUXCFG0_ADDR_ONLY;
+
+	return auxcfg0;
+}
+
 static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
 			       struct drm_dp_aux_msg *msg)
 {
@@ -326,9 +340,6 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
 	u32 auxstatus;
 	int ret;
 
-	if (size == 0)
-		return 0;
-
 	ret = tc_aux_wait_busy(tc);
 	if (ret)
 		return ret;
@@ -339,9 +350,11 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
 		break;
 	case DP_AUX_NATIVE_WRITE:
 	case DP_AUX_I2C_WRITE:
+		if (size) {
 			ret = tc_aux_write_data(tc, msg->buffer, size);
 			if (ret < 0)
 				return ret;
+		}
 		break;
 	default:
 		return -EINVAL;
@@ -352,8 +365,7 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
 	if (ret)
 		return ret;
 	/* Start transfer */
-	ret = regmap_write(tc->regmap, DP0_AUXCFG0,
-			   ((size - 1) << 8) | request);
+	ret = regmap_write(tc->regmap, DP0_AUXCFG0, tc_auxcfg0(msg, size));
 	if (ret)
 		return ret;
 
@@ -367,14 +379,22 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
 
 	if (auxstatus & AUX_TIMEOUT)
 		return -ETIMEDOUT;
-
+	/*
+	 * For some reason address-only DP_AUX_I2C_WRITE (MOT), still
+	 * reports 1 byte transferred in its status. To deal we that
+	 * we ignore aux_bytes field if we know that this was an
+	 * address-only transfer
+	 */
+	if (size)
 		size = FIELD_GET(AUX_BYTES, auxstatus);
 	msg->reply = FIELD_GET(AUX_STATUS, auxstatus);
 
 	switch (request) {
 	case DP_AUX_NATIVE_READ:
 	case DP_AUX_I2C_READ:
+		if (size)
 			return tc_aux_read_data(tc, msg->buffer, size);
+		break;
 	}
 
 	return size;