Commit 96219c3a authored by Doug Anderson's avatar Doug Anderson Committed by Ben Dooks
Browse files

i2c-tegra: fix possible race condition after tx 



In tegra_i2c_fill_tx_fifo, once we have finished pushing all the bytes
to the I2C hardware controller, the interrupt might happen before we
have updated i2c_dev->msg_buf_remaining at the end of the function.
Then, in tegra_i2c_isr, we will call again tegra_i2c_fill_tx_fifo
triggering weird behaviour. This has been shown to happen under real
conditions.

Signed-off-by: default avatarDoug Anderson <dianders@chromium.org>
Tested-by: default avatarVincent Palatin <vpalatin@chromium.org>
Acked-by: default avatarRhyland Klein <rklein@nvidia.com>
Acked-by: default avatarStephen Warren <swarren@nvidia.com>
Signed-off-by: default avatarStephen Warren <swarren@nvidia.com>
Signed-off-by: default avatarBen Dooks <ben-linux@fluff.org>
parent 048e29cf

drivers/i2c/busses/i2c-tegra.c

+32 −14
Original line number Diff line number Diff line
@@ -270,14 +270,30 @@ static int tegra_i2c_fill_tx_fifo(struct tegra_i2c_dev *i2c_dev) 


	/* Rounds down to not include partial word at the end of buf */

	words_to_transfer = buf_remaining / BYTES_PER_FIFO_WORD;



	/* It's very common to have < 4 bytes, so optimize that case. */

	if (words_to_transfer) {

		if (words_to_transfer > tx_fifo_avail)

			words_to_transfer = tx_fifo_avail;



		/*

		 * Update state before writing to FIFO.  If this casues us

		 * to finish writing all bytes (AKA buf_remaining goes to 0) we

		 * have a potential for an interrupt (PACKET_XFER_COMPLETE is

		 * not maskable).  We need to make sure that the isr sees

		 * buf_remaining as 0 and doesn't call us back re-entrantly.

		 */

		buf_remaining -= words_to_transfer * BYTES_PER_FIFO_WORD;

		tx_fifo_avail -= words_to_transfer;

		i2c_dev->msg_buf_remaining = buf_remaining;

		i2c_dev->msg_buf = buf +

			words_to_transfer * BYTES_PER_FIFO_WORD;

		barrier();



		i2c_writesl(i2c_dev, buf, I2C_TX_FIFO, words_to_transfer);



		buf += words_to_transfer * BYTES_PER_FIFO_WORD;

	buf_remaining -= words_to_transfer * BYTES_PER_FIFO_WORD;

	tx_fifo_avail -= words_to_transfer;

	}



	/*

	 * If there is a partial word at the end of buf, handle it manually to
@@ -287,14 +303,15 @@ static int tegra_i2c_fill_tx_fifo(struct tegra_i2c_dev *i2c_dev) 
	if (tx_fifo_avail > 0 && buf_remaining > 0) {

		BUG_ON(buf_remaining > 3);

		memcpy(&val, buf, buf_remaining);



		/* Again update before writing to FIFO to make sure isr sees. */

		i2c_dev->msg_buf_remaining = 0;

		i2c_dev->msg_buf = NULL;

		barrier();



		i2c_writel(i2c_dev, val, I2C_TX_FIFO);

		buf_remaining = 0;

		tx_fifo_avail--;

	}



	BUG_ON(tx_fifo_avail > 0 && buf_remaining > 0);

	i2c_dev->msg_buf_remaining = buf_remaining;

	i2c_dev->msg_buf = buf;

	return 0;

}
@@ -411,9 +428,10 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id) 
			tegra_i2c_mask_irq(i2c_dev, I2C_INT_TX_FIFO_DATA_REQ);

	}



	if ((status & I2C_INT_PACKET_XFER_COMPLETE) &&

			!i2c_dev->msg_buf_remaining)

	if (status & I2C_INT_PACKET_XFER_COMPLETE) {

		BUG_ON(i2c_dev->msg_buf_remaining);

		complete(&i2c_dev->msg_complete);

	}



	i2c_writel(i2c_dev, status, I2C_INT_STATUS);

	if (i2c_dev->is_dvc)

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