[PATCH v2 07/15] drm/bridge: tc358767: Simplify AUX data write

[Andrey Smirnov]

Simplify AUX data write by dropping index arithmetic and shifting and
replacing it with a call to a helper function that does three things:

    1. Copies user-provided data into a write buffer
    2. Optionally fixes the endianness of the write buffer (not needed
       on LE hosts)
    3. Transfers contenst of the write buffer to up to 4 32-bit
       registers on the chip

Note that separate data endianness fix:

    tmp = (tmp << 8) | buf[i];

that was reserved for DP_AUX_I2C_WRITE looks really strange, since it
will place data differently depending on the passed user-data
size. E.g. for a write of 1 byte, data transferred to the chip would
look like:

[byte0] [dummy1] [dummy2] [dummy3]

whereas for a write of 4 bytes we'd get:

[byte3] [byte2] [byte1] [byte0]

Since there's no indication in the datasheet that I2C write buffer
should be treated differently than AUX write buffer and no comment in
the original code explaining why it was done this way, that special
I2C write buffer transformation was dropped in this patch.

Signed-off-by: Andrey Smirnov <andrew.smirnov at gmail.com>
Cc: Archit Taneja <architt at codeaurora.org>
Cc: Andrzej Hajda <a.hajda at samsung.com>
Cc: Laurent Pinchart <Laurent.pinchart at ideasonboard.com>
Cc: Tomi Valkeinen <tomi.valkeinen at ti.com>
Cc: Andrey Gusakov <andrey.gusakov at cogentembedded.com>
Cc: Philipp Zabel <p.zabel at pengutronix.de>
Cc: Chris Healy <cphealy at gmail.com>
Cc: Lucas Stach <l.stach at pengutronix.de>
Cc: dri-devel at lists.freedesktop.org
Cc: linux-kernel at vger.kernel.org
---
 drivers/gpu/drm/bridge/tc358767.c | 58 +++++++++++++++++++------------
 1 file changed, 36 insertions(+), 22 deletions(-)

diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c
index 81c10a5d8106..21374565585d 100644
--- a/drivers/gpu/drm/bridge/tc358767.c
+++ b/drivers/gpu/drm/bridge/tc358767.c
@@ -307,6 +307,31 @@ static int tc_aux_get_status(struct tc_data *tc, u8 *reply)
 	return 0;
 }
 
+static int tc_aux_write_data(struct tc_data *tc, const void *data,
+			     size_t size)
+{
+	u32 auxwdata[DP_AUX_MAX_PAYLOAD_BYTES / sizeof(u32)] = { 0 };
+	int ret, i, count = DIV_ROUND_UP(size, 4);
+
+	memcpy(auxwdata, data, size);
+
+	for (i = 0; i < count; i++) {
+		ret = regmap_write(tc->regmap, DP0_AUXWDATA(i),
+				   /*
+				    * Our regmap is configured as LE
+				    * for register data, so we need
+				    * undo any byte swapping that will
+				    * happened to preserve original
+				    * byte order.
+				    */
+				   cpu_to_le32(auxwdata[i]));
+		if (ret)
+			return ret;
+	}
+
+	return size;
+}
+
 static int tc_aux_read_data(struct tc_data *tc, void *data, size_t size)
 {
 	u32 auxrdata[DP_AUX_MAX_PAYLOAD_BYTES / sizeof(u32)];
@@ -335,9 +360,6 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
 	struct tc_data *tc = aux_to_tc(aux);
 	size_t size = min_t(size_t, 8, msg->size);
 	u8 request = msg->request & ~DP_AUX_I2C_MOT;
-	u8 *buf = msg->buffer;
-	u32 tmp = 0;
-	int i = 0;
 	int ret;
 
 	if (size == 0)
@@ -347,25 +369,17 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
 	if (ret)
 		return ret;
 
-	if (request == DP_AUX_I2C_WRITE || request == DP_AUX_NATIVE_WRITE) {
-		/* Store data */
-		while (i < size) {
-			if (request == DP_AUX_NATIVE_WRITE)
-				tmp = tmp | (buf[i] << (8 * (i & 0x3)));
-			else
-				tmp = (tmp << 8) | buf[i];
-			i++;
-			if (((i % 4) == 0) || (i == size)) {
-				ret = regmap_write(tc->regmap,
-						   DP0_AUXWDATA((i - 1) >> 2),
-						   tmp);
-				if (ret)
-					return ret;
-				tmp = 0;
-			}
-		}
-	} else if (request != DP_AUX_I2C_READ &&
-		   request != DP_AUX_NATIVE_READ) {
+	switch (request) {
+	case DP_AUX_NATIVE_READ:
+	case DP_AUX_I2C_READ:
+		break;
+	case DP_AUX_NATIVE_WRITE:
+	case DP_AUX_I2C_WRITE:
+		ret = tc_aux_write_data(tc, msg->buffer, size);
+		if (ret < 0)
+			return ret;
+		break;
+	default:
 		return -EINVAL;
 	}
 
-- 
2.20.1