[PATCH v5 0/2] Tegra I2C DMA and SMBus blockread updates

[PATCH v5 0/2] Tegra I2C DMA and SMBus blockread updates

[Akhil R]

The patchset contains two independent updates to tegra-i2c driver.
* Update I2C DMA channel usage to use single DMA channel instead of
two different hardware channels.
* Fix PEC byte issue during SMBus block read caused by mismanaged
msg->len property in i2c_msg struct.

v4->v5:
 Corrected the comment style
v3->v4:
 Combine the two patches to one series to avoid merge conflicts.

Akhil R (2):
  i2c: tegra: Fix PEC support for SMBUS block read
  i2c: tegra: Share same DMA channel for RX and TX

 drivers/i2c/busses/i2c-tegra.c | 107 ++++++++++++++-------------------
 1 file changed, 46 insertions(+), 61 deletions(-)

-- 
2.17.1

[PATCH v5 1/2] i2c: tegra: Fix PEC support for SMBUS block read

[Akhil R]

Update the msg->len value correctly for SMBUS block read. The discrepancy
went unnoticed as msg->len is used in SMBUS transfers only when a PEC
byte is added.

Fixes: d7583c8a5748 ("i2c: tegra: Add SMBus block read function")
Signed-off-by: Akhil R <akhilrajeev@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
---
 drivers/i2c/busses/i2c-tegra.c | 38 +++++++++++++++++++++++-----------
 1 file changed, 26 insertions(+), 12 deletions(-)

diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
index 6aab84c8d22b..c1e1e1c2b8d9 100644
--- a/drivers/i2c/busses/i2c-tegra.c
+++ b/drivers/i2c/busses/i2c-tegra.c
@@ -245,6 +245,7 @@ struct tegra_i2c_hw_feature {
  * @msg_err: error code for completed message
  * @msg_buf: pointer to current message data
  * @msg_buf_remaining: size of unsent data in the message buffer
+ * @msg_len: length of message in current transfer
  * @msg_read: indicates that the transfer is a read access
  * @timings: i2c timings information like bus frequency
  * @multimaster_mode: indicates that I2C controller is in multi-master mode
@@ -279,6 +280,7 @@ struct tegra_i2c_dev {
 	size_t msg_buf_remaining;
 	int msg_err;
 	u8 *msg_buf;
+	__u16 msg_len;
 
 	struct completion dma_complete;
 	struct dma_chan *tx_dma_chan;
@@ -1169,7 +1171,7 @@ static void tegra_i2c_push_packet_header(struct tegra_i2c_dev *i2c_dev,
 	else
 		i2c_writel(i2c_dev, packet_header, I2C_TX_FIFO);
 
-	packet_header = msg->len - 1;
+	packet_header = i2c_dev->msg_len - 1;
 
 	if (i2c_dev->dma_mode && !i2c_dev->msg_read)
 		*dma_buf++ = packet_header;
@@ -1242,20 +1244,32 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
 		return err;
 
 	i2c_dev->msg_buf = msg->buf;
+	i2c_dev->msg_len = msg->len;
 
-	/* The condition true implies smbus block read and len is already read */
-	if (msg->flags & I2C_M_RECV_LEN && end_state != MSG_END_CONTINUE)
-		i2c_dev->msg_buf = msg->buf + 1;
-
-	i2c_dev->msg_buf_remaining = msg->len;
 	i2c_dev->msg_err = I2C_ERR_NONE;
 	i2c_dev->msg_read = !!(msg->flags & I2C_M_RD);
 	reinit_completion(&i2c_dev->msg_complete);
 
+	/*
+	 * For SMBUS block read command, read only 1 byte in the first transfer.
+	 * Adjust that 1 byte for the next transfer in the msg buffer and msg
+	 * length.
+	 */
+	if (msg->flags & I2C_M_RECV_LEN) {
+		if (end_state == MSG_END_CONTINUE) {
+			i2c_dev->msg_len = 1;
+		} else {
+			i2c_dev->msg_buf += 1;
+			i2c_dev->msg_len -= 1;
+		}
+	}
+
+	i2c_dev->msg_buf_remaining = i2c_dev->msg_len;
+
 	if (i2c_dev->msg_read)
-		xfer_size = msg->len;
+		xfer_size = i2c_dev->msg_len;
 	else
-		xfer_size = msg->len + I2C_PACKET_HEADER_SIZE;
+		xfer_size = i2c_dev->msg_len + I2C_PACKET_HEADER_SIZE;
 
 	xfer_size = ALIGN(xfer_size, BYTES_PER_FIFO_WORD);
 
@@ -1295,7 +1309,7 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
 	if (!i2c_dev->msg_read) {
 		if (i2c_dev->dma_mode) {
 			memcpy(i2c_dev->dma_buf + I2C_PACKET_HEADER_SIZE,
-			       msg->buf, msg->len);
+			       msg->buf, i2c_dev->msg_len);
 
 			dma_sync_single_for_device(i2c_dev->dma_dev,
 						   i2c_dev->dma_phys,
@@ -1352,7 +1366,7 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
 						i2c_dev->dma_phys,
 						xfer_size, DMA_FROM_DEVICE);
 
-			memcpy(i2c_dev->msg_buf, i2c_dev->dma_buf, msg->len);
+			memcpy(i2c_dev->msg_buf, i2c_dev->dma_buf, i2c_dev->msg_len);
 		}
 	}
 
@@ -1408,8 +1422,8 @@ static int tegra_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
 			ret = tegra_i2c_xfer_msg(i2c_dev, &msgs[i], MSG_END_CONTINUE);
 			if (ret)
 				break;
-			/* Set the read byte as msg len */
-			msgs[i].len = msgs[i].buf[0];
+			/* Set the msg length from first byte */
+			msgs[i].len += msgs[i].buf[0];
 			dev_dbg(i2c_dev->dev, "reading %d bytes\n", msgs[i].len);
 		}
 		ret = tegra_i2c_xfer_msg(i2c_dev, &msgs[i], end_type);
-- 
2.17.1

[PATCH v5 2/2] i2c: tegra: Share same DMA channel for RX and TX

[Akhil R]

Allocate only one DMA channel for I2C and share it for both TX and RX
instead of using two different DMA hardware channels with the same
slave ID. Since I2C supports only half duplex, there is no impact on
perf with this.

Signed-off-by: Akhil R <akhilrajeev@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
---
 drivers/i2c/busses/i2c-tegra.c | 69 ++++++++++------------------------
 1 file changed, 20 insertions(+), 49 deletions(-)

diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
index c1e1e1c2b8d9..fe042232a181 100644
--- a/drivers/i2c/busses/i2c-tegra.c
+++ b/drivers/i2c/busses/i2c-tegra.c
@@ -249,8 +249,7 @@ struct tegra_i2c_hw_feature {
  * @msg_read: indicates that the transfer is a read access
  * @timings: i2c timings information like bus frequency
  * @multimaster_mode: indicates that I2C controller is in multi-master mode
- * @tx_dma_chan: DMA transmit channel
- * @rx_dma_chan: DMA receive channel
+ * @dma_chan: DMA channel
  * @dma_phys: handle to DMA resources
  * @dma_buf: pointer to allocated DMA buffer
  * @dma_buf_size: DMA buffer size
@@ -283,8 +282,7 @@ struct tegra_i2c_dev {
 	__u16 msg_len;
 
 	struct completion dma_complete;
-	struct dma_chan *tx_dma_chan;
-	struct dma_chan *rx_dma_chan;
+	struct dma_chan *dma_chan;
 	unsigned int dma_buf_size;
 	struct device *dma_dev;
 	dma_addr_t dma_phys;
@@ -393,16 +391,14 @@ static int tegra_i2c_dma_submit(struct tegra_i2c_dev *i2c_dev, size_t len)
 {
 	struct dma_async_tx_descriptor *dma_desc;
 	enum dma_transfer_direction dir;
-	struct dma_chan *chan;
 
 	dev_dbg(i2c_dev->dev, "starting DMA for length: %zu\n", len);
 
 	reinit_completion(&i2c_dev->dma_complete);
 
 	dir = i2c_dev->msg_read ? DMA_DEV_TO_MEM : DMA_MEM_TO_DEV;
-	chan = i2c_dev->msg_read ? i2c_dev->rx_dma_chan : i2c_dev->tx_dma_chan;
 
-	dma_desc = dmaengine_prep_slave_single(chan, i2c_dev->dma_phys,
+	dma_desc = dmaengine_prep_slave_single(i2c_dev->dma_chan, i2c_dev->dma_phys,
 					       len, dir, DMA_PREP_INTERRUPT |
 					       DMA_CTRL_ACK);
 	if (!dma_desc) {
@@ -415,7 +411,7 @@ static int tegra_i2c_dma_submit(struct tegra_i2c_dev *i2c_dev, size_t len)
 	dma_desc->callback_param = i2c_dev;
 
 	dmaengine_submit(dma_desc);
-	dma_async_issue_pending(chan);
+	dma_async_issue_pending(i2c_dev->dma_chan);
 
 	return 0;
 }
@@ -428,20 +424,14 @@ static void tegra_i2c_release_dma(struct tegra_i2c_dev *i2c_dev)
 		i2c_dev->dma_buf = NULL;
 	}
 
-	if (i2c_dev->tx_dma_chan) {
-		dma_release_channel(i2c_dev->tx_dma_chan);
-		i2c_dev->tx_dma_chan = NULL;
-	}
-
-	if (i2c_dev->rx_dma_chan) {
-		dma_release_channel(i2c_dev->rx_dma_chan);
-		i2c_dev->rx_dma_chan = NULL;
+	if (i2c_dev->dma_chan) {
+		dma_release_channel(i2c_dev->dma_chan);
+		i2c_dev->dma_chan = NULL;
 	}
 }
 
 static int tegra_i2c_init_dma(struct tegra_i2c_dev *i2c_dev)
 {
-	struct dma_chan *chan;
 	dma_addr_t dma_phys;
 	u32 *dma_buf;
 	int err;
@@ -459,25 +449,18 @@ static int tegra_i2c_init_dma(struct tegra_i2c_dev *i2c_dev)
 		return 0;
 	}
 
-	chan = dma_request_chan(i2c_dev->dev, "rx");
-	if (IS_ERR(chan)) {
-		err = PTR_ERR(chan);
-		goto err_out;
-	}
-
-	i2c_dev->rx_dma_chan = chan;
-
-	chan = dma_request_chan(i2c_dev->dev, "tx");
-	if (IS_ERR(chan)) {
-		err = PTR_ERR(chan);
+	/*
+	 * The same channel will be used for both RX and TX.
+	 * Keeping the name as "tx" for backward compatibility
+	 * with existing devicetrees.
+	 */
+	i2c_dev->dma_chan = dma_request_chan(i2c_dev->dev, "tx");
+	if (IS_ERR(i2c_dev->dma_chan)) {
+		err = PTR_ERR(i2c_dev->dma_chan);
 		goto err_out;
 	}
 
-	i2c_dev->tx_dma_chan = chan;
-
-	WARN_ON(i2c_dev->tx_dma_chan->device != i2c_dev->rx_dma_chan->device);
-	i2c_dev->dma_dev = chan->device->dev;
-
+	i2c_dev->dma_dev = i2c_dev->dma_chan->device->dev;
 	i2c_dev->dma_buf_size = i2c_dev->hw->quirks->max_write_len +
 				I2C_PACKET_HEADER_SIZE;
 
@@ -976,11 +959,7 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)
 		dvc_writel(i2c_dev, DVC_STATUS_I2C_DONE_INTR, DVC_STATUS);
 
 	if (i2c_dev->dma_mode) {
-		if (i2c_dev->msg_read)
-			dmaengine_terminate_async(i2c_dev->rx_dma_chan);
-		else
-			dmaengine_terminate_async(i2c_dev->tx_dma_chan);
-
+		dmaengine_terminate_async(i2c_dev->dma_chan);
 		complete(&i2c_dev->dma_complete);
 	}
 
@@ -994,7 +973,6 @@ static void tegra_i2c_config_fifo_trig(struct tegra_i2c_dev *i2c_dev,
 {
 	struct dma_slave_config slv_config = {0};
 	u32 val, reg, dma_burst, reg_offset;
-	struct dma_chan *chan;
 	int err;
 
 	if (i2c_dev->hw->has_mst_fifo)
@@ -1011,7 +989,6 @@ static void tegra_i2c_config_fifo_trig(struct tegra_i2c_dev *i2c_dev,
 			dma_burst = 8;
 
 		if (i2c_dev->msg_read) {
-			chan = i2c_dev->rx_dma_chan;
 			reg_offset = tegra_i2c_reg_addr(i2c_dev, I2C_RX_FIFO);
 
 			slv_config.src_addr = i2c_dev->base_phys + reg_offset;
@@ -1023,7 +1000,6 @@ static void tegra_i2c_config_fifo_trig(struct tegra_i2c_dev *i2c_dev,
 			else
 				val = I2C_FIFO_CONTROL_RX_TRIG(dma_burst);
 		} else {
-			chan = i2c_dev->tx_dma_chan;
 			reg_offset = tegra_i2c_reg_addr(i2c_dev, I2C_TX_FIFO);
 
 			slv_config.dst_addr = i2c_dev->base_phys + reg_offset;
@@ -1037,7 +1013,7 @@ static void tegra_i2c_config_fifo_trig(struct tegra_i2c_dev *i2c_dev,
 		}
 
 		slv_config.device_fc = true;
-		err = dmaengine_slave_config(chan, &slv_config);
+		err = dmaengine_slave_config(i2c_dev->dma_chan, &slv_config);
 		if (err) {
 			dev_err(i2c_dev->dev, "DMA config failed: %d\n", err);
 			dev_err(i2c_dev->dev, "falling back to PIO\n");
@@ -1347,13 +1323,8 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
 		 * performs synchronization after the transfer's termination
 		 * and we want to get a completion if transfer succeeded.
 		 */
-		dmaengine_synchronize(i2c_dev->msg_read ?
-				      i2c_dev->rx_dma_chan :
-				      i2c_dev->tx_dma_chan);
-
-		dmaengine_terminate_sync(i2c_dev->msg_read ?
-					 i2c_dev->rx_dma_chan :
-					 i2c_dev->tx_dma_chan);
+		dmaengine_synchronize(i2c_dev->dma_chan);
+		dmaengine_terminate_sync(i2c_dev->dma_chan);
 
 		if (!time_left && !completion_done(&i2c_dev->dma_complete)) {
 			dev_err(i2c_dev->dev, "DMA transfer timed out\n");
-- 
2.17.1

Re: [PATCH v5 1/2] i2c: tegra: Fix PEC support for SMBUS block read

[Dmitry Osipenko]

On 4/13/23 16:08, Akhil R wrote:
> @@ -279,6 +280,7 @@ struct tegra_i2c_dev {
>  	size_t msg_buf_remaining;
>  	int msg_err;
>  	u8 *msg_buf;
> +	__u16 msg_len;

It's still __u16

-- 
Best regards,
Dmitry

RE: [PATCH v5 1/2] i2c: tegra: Fix PEC support for SMBUS block read

[Akhil R]

> On 4/13/23 16:08, Akhil R wrote:
> > @@ -279,6 +280,7 @@ struct tegra_i2c_dev {
> >       size_t msg_buf_remaining;
> >       int msg_err;
> >       u8 *msg_buf;
> > +     __u16 msg_len;
> 
> It's still __u16
Oh. I totally missed that comment. Will update.

Thanks,
Akhil