i2c: sh_mobile: use core helper to decide when to use DMA

This ensures that we fall back to PIO if the message length is too small
for DMA being useful. Otherwise, we use DMA. A bounce buffer might be
applied by the helper if the original message buffer is not DMA safe.
Reviewed-by: NJonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: NWolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: NWolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-sh_mobile.c

@@ -144,6 +144,7 @@ struct sh_mobile_i2c_data {
 	struct dma_chan *dma_rx;
 	struct scatterlist sg;
 	enum dma_data_direction dma_direction;
+	u8 *dma_buf;
 };
 
 struct sh_mobile_dt_config {
@@ -501,6 +502,8 @@ static void sh_mobile_i2c_dma_callback(void *data)
 	pd->pos = pd->msg->len;
 	pd->stop_after_dma = true;
 
+	i2c_release_dma_safe_msg_buf(pd->msg, pd->dma_buf);
+
 	iic_set_clr(pd, ICIC, 0, ICIC_TDMAE | ICIC_RDMAE);
 }
 
@@ -561,7 +564,7 @@ static void sh_mobile_i2c_xfer_dma(struct sh_mobile_i2c_data *pd)
 	if (IS_ERR(chan))
 		return;
 
-	dma_addr = dma_map_single(chan->device->dev, pd->msg->buf, pd->msg->len, dir);
+	dma_addr = dma_map_single(chan->device->dev, pd->dma_buf, pd->msg->len, dir);
 	if (dma_mapping_error(chan->device->dev, dma_addr)) {
 		dev_dbg(pd->dev, "dma map failed, using PIO\n");
 		return;
@@ -618,7 +621,8 @@ static int start_ch(struct sh_mobile_i2c_data *pd, struct i2c_msg *usr_msg,
 	pd->pos = -1;
 	pd->sr = 0;
 
-	if (pd->msg->len > 8)
+	pd->dma_buf = i2c_get_dma_safe_msg_buf(pd->msg, 8);
+	if (pd->dma_buf)
 		sh_mobile_i2c_xfer_dma(pd);
 
 	/* Enable all interrupts to begin with */