Re: [PATCH V6] i2c: tegra: remove BUG, BUG_ON

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On 6/14/19 10:51 AM, Dmitry Osipenko wrote:
14.06.2019 18:50, Bitan Biswas пишет:
Remove redundant BUG_ON calls or replace with WARN_ON_ONCE
as needed. Remove BUG() and mask Rx interrupt similar as Tx
for message fully sent case. Add WARN_ON_ONCE check
for non-zero rx_fifo_avail in tegra_i2c_empty_rx_fifo()
after all processing. Error handling in tegra_i2c_empty_rx_fifo
caller is also added.

Signed-off-by: Bitan Biswas <bbiswas@xxxxxxxxxx>
---
  drivers/i2c/busses/i2c-tegra.c | 46 ++++++++++++++++++++++++++++++++++--------
  1 file changed, 38 insertions(+), 8 deletions(-)

diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
index 4dfb4c1..26a7c8c 100644
--- a/drivers/i2c/busses/i2c-tegra.c
+++ b/drivers/i2c/busses/i2c-tegra.c
@@ -73,6 +73,7 @@
  #define I2C_ERR_NO_ACK				BIT(0)
  #define I2C_ERR_ARBITRATION_LOST		BIT(1)
  #define I2C_ERR_UNKNOWN_INTERRUPT		BIT(2)
+#define I2C_ERR_UNEXPECTED_STATUS		BIT(3)

What about I2C_ERR_RX_BUFFER_OVERFLOW?
OK.


  #define PACKET_HEADER0_HEADER_SIZE_SHIFT	28
  #define PACKET_HEADER0_PACKET_ID_SHIFT		16
@@ -515,15 +516,23 @@ static int tegra_i2c_empty_rx_fifo(struct tegra_i2c_dev *i2c_dev)
  	 * prevent overwriting past the end of buf
  	 */
  	if (rx_fifo_avail > 0 && buf_remaining > 0) {
-		BUG_ON(buf_remaining > 3);
+		/* buf_remaining > 3 check not needed as rx_fifo_avail == 0
+		 * when (words_to_transfer was > rx_fifo_avail) earlier
+		 * in this function
+		 */

Please start all multiline comments with an empty "/*", it should be the correct
style. There are some places in the kernel where style like yours is used, but I
assume they are not very correct. Besides, yours variant is not consistent with the
style of the rest of comments in this source file. And put a dot in the end for
completeness. Same for the other comments in this patch.

OK

  		val = i2c_readl(i2c_dev, I2C_RX_FIFO);
  		val = cpu_to_le32(val);
  		memcpy(buf, &val, buf_remaining);
  		buf_remaining = 0;
  		rx_fifo_avail--;
  	}

Please add a newline here. All logical parts of the code should be separated to ease
reading and following.
OK


+	if (WARN_ON_ONCE(rx_fifo_avail))
+		return -EINVAL;
- BUG_ON(rx_fifo_avail > 0 && buf_remaining > 0);
+	/* buf_remaining > 0 at this point can only have rx_fifo_avail == 0
+	 * as this corresponds to (words_to_transfer was > rx_fifo_avail)
+	 * case earlier in this function
+	 */
  	i2c_dev->msg_buf_remaining = buf_remaining;
  	i2c_dev->msg_buf = buf;
@@ -581,7 +590,10 @@ static int tegra_i2c_fill_tx_fifo(struct tegra_i2c_dev *i2c_dev)
  	 * boundary and fault.
  	 */
  	if (tx_fifo_avail > 0 && buf_remaining > 0) {
-		BUG_ON(buf_remaining > 3);
+		/* buf_remaining > 3 check not needed as tx_fifo_avail == 0
+		 * when (words_to_transfer was > tx_fifo_avail) earlier
+		 * in this function for non-zero words_to_transfer
+		 */
  		memcpy(&val, buf, buf_remaining);
  		val = le32_to_cpu(val);
@@ -811,6 +823,7 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)
  	u32 status;
  	const u32 status_err = I2C_INT_NO_ACK | I2C_INT_ARBITRATION_LOST;
  	struct tegra_i2c_dev *i2c_dev = dev_id;
+	int err_val;
status = i2c_readl(i2c_dev, I2C_INT_STATUS); @@ -847,10 +860,21 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id) if (!i2c_dev->is_curr_dma_xfer) {
  		if (i2c_dev->msg_read && (status & I2C_INT_RX_FIFO_DATA_REQ)) {
-			if (i2c_dev->msg_buf_remaining)
-				tegra_i2c_empty_rx_fifo(i2c_dev);
-			else
-				BUG();
+			err_val = tegra_i2c_empty_rx_fifo(i2c_dev);
+			if ((!(i2c_dev->msg_buf_remaining)) &&

Let's move this check into tegra_i2c_empty_rx_fifo() and return -EINVAL for that case.
This will make code to look cleaner.
OK.



+			    (!(status & I2C_INT_PACKET_XFER_COMPLETE)) &&

It shouldn't matter that XFER_COMPLETE is set if RX FIFO isn't fully emptied because
it always shall be emptied. Hence this check is not needed and we should error out
regardless.
OK


+			    err_val) {
+				/*
+				 * Overflow error condition: message fully sent,
+				 * with no XFER_COMPLETE interrupt but hardware
+				 * asks to transfer more.
+				 */
+				tegra_i2c_mask_irq(i2c_dev,
+						   I2C_INT_RX_FIFO_DATA_REQ);

No need to mask RX_FIFO_DATA_REQ here because all interrupts are masked on "goto
err:", hence just remove the tegra_i2c_mask_irq().

+				i2c_dev->msg_err |=
+					I2C_ERR_UNEXPECTED_STATUS;

No need to split this into two lines because it's less than 80 chars, write this in a
single line.
OK


+				goto err;
+			}
  		}
if (!i2c_dev->msg_read && (status & I2C_INT_TX_FIFO_DATA_REQ)) {
@@ -876,7 +900,13 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)
  	if (status & I2C_INT_PACKET_XFER_COMPLETE) {
  		if (i2c_dev->is_curr_dma_xfer)
  			i2c_dev->msg_buf_remaining = 0;
-		BUG_ON(i2c_dev->msg_buf_remaining);
+		/* Underflow error condition: XFER_COMPLETE before message
+		 * fully sent.
+		 */
+		if (WARN_ON_ONCE(i2c_dev->msg_buf_remaining)) {
+			i2c_dev->msg_err |= I2C_ERR_UNKNOWN_INTERRUPT;
+			goto err;
+		}
  		complete(&i2c_dev->msg_complete);
  	}
  	goto done;


Please address comments in the next revision.


Sorry for the delayed reply. I shared Patch V7 with above changes earlier today.

-regards,
 Bitan





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