linux-kernel - [RFC PATCH v5 4/6] i2c: sh_mobile: use helper to decide if DMA is useful

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Message-Id: <20170920185956.13874-5-wsa+renesas@sang-engineering.com>
Date:   Wed, 20 Sep 2017 20:59:54 +0200
From:   Wolfram Sang <wsa+renesas@...g-engineering.com>
To:     linux-i2c@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-iio@...r.kernel.org, linux-input@...r.kernel.org,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Wolfram Sang <wsa+renesas@...g-engineering.com>
Subject: [RFC PATCH v5 4/6] i2c: sh_mobile: use helper to decide if DMA is useful

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@...g-engineering.com>
---
 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 6f2aaeb7c4fa15..b76399d8a3abd3 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