[PATCH] i2c: i2c_cdns: fix write timeout on fifo boundary

[Simon Glass]

On Mon, 9 Dec 2019 at 11:19, Michael Auchter <michael.auchter at ni.com> wrote:
>
> This fixes an issue that would cause I2C writes to timeout when the
> number of bytes is a multiple of the FIFO depth (i.e. 16 bytes).
>
> Within the transfer loop, after writing the data register with a new
> byte to transfer, if the transfer size equals the FIFO depth, the loop
> pauses until the INTERRUPT_COMP bit asserts to indicate data has been
> sent. This same check is performed after the loop as well to ensure data
> has been transferred prior to returning.
>
> In the case where the amount of data to be written is a multiple of the
> FIFO depth, the transfer loop would wait for the INTERRUPT_COMP bit to
> assert after writing the final byte, and then wait for this bit to
> assert once more. However, since the transfer has finished at this
> point, no new data has been written to the data register, and hence
> INTERRUPT_COMP will never assert.
>
> Fix this by only waiting for INTERRUPT_COMP in the transfer loop if
> there's still data to be written.
>
> Signed-off-by: Michael Auchter <michael.auchter at ni.com>
> ---
>  drivers/i2c/i2c-cdns.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/i2c/i2c-cdns.c b/drivers/i2c/i2c-cdns.c
> index 2c0301ad08..ff3956d8c2 100644
> --- a/drivers/i2c/i2c-cdns.c
> +++ b/drivers/i2c/i2c-cdns.c
> @@ -265,7 +265,7 @@ static int cdns_i2c_write_data(struct i2c_cdns_bus *i2c_bus, u32 addr, u8 *data,
>
>         while (len-- && !is_arbitration_lost(regs)) {
>                 writel(*(cur_data++), &regs->data);
> -               if (readl(&regs->transfer_size) == CDNS_I2C_FIFO_DEPTH) {
> +               if (len && readl(&regs->transfer_size) == CDNS_I2C_FIFO_DEPTH) {
>                         ret = cdns_i2c_wait(regs, CDNS_I2C_INTERRUPT_COMP |
>                                             CDNS_I2C_INTERRUPT_ARBLOST);
>                         if (ret & CDNS_I2C_INTERRUPT_ARBLOST)
> --
> 2.23.0
>

Reviewed-by: Simon Glass <sjg at chromium.org>