Re: [PATCH v4 15/31] i2c: tegra: Remove bogus barrier()

Dmitry Osipenko
2020-09-05T23:35:14Z

05.09.2020 23:41, Dmitry Osipenko пишет:
> Apparently barrier() was intended to reduce possibility of racing
> with the interrupt handler, but driver's code evolved significantly
> and today's driver enables interrupt only when it waits for completion
> notification. Hence barrier() has no good use anymore, let's remove it.
>
> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> ---
> drivers/i2c/busses/i2c-tegra.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> index 33d37a40fa83..f69587ca163b 100644
> --- a/drivers/i2c/busses/i2c-tegra.c
> +++ b/drivers/i2c/busses/i2c-tegra.c
> @@ -600,7 +600,6 @@ static int tegra_i2c_fill_tx_fifo(struct tegra_i2c_dev *i2c_dev)
> 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);
>
> @@ -624,7 +623,6 @@ static int tegra_i2c_fill_tx_fifo(struct tegra_i2c_dev *i2c_dev)
> /* 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);
> }
>

It just caught my eye that there is actually a comment there saying that
barrier() was intended to mitigate the racing with the ISR. Hence that
comment is outdated now and needs to be removed. I'll correct it in v5.