[RFC PATCH v4 4/6] i2c: sh_mobile: use helper to decide if DMA is useful

[Wolfram Sang]

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.

Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
---
 drivers/i2c/busses/i2c-sh_mobile.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-sh_mobile.c b/drivers/i2c/busses/i2c-sh_mobile.c
index 2e097d97d258bc..5efdb7becd83d6 100644
--- a/drivers/i2c/busses/i2c-sh_mobile.c
+++ b/drivers/i2c/busses/i2c-sh_mobile.c
@@ -145,6 +145,7 @@ 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 {
@@ -548,6 +549,8 @@ 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);
 }
 
@@ -608,7 +611,7 @@ 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;
@@ -665,7 +668,8 @@ 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 */
-- 
2.11.0