Re: [PATCH 2/4] i2c: rockchip: ignore i2c transfers when another transfer is running

[Sascha Hauer <sha@pengutronix.de>]

On Fri, Sep 08, 2023 at 12:16:47PM +0200, Gerald Loacker wrote:
> It may happen that an i2c transfer is requested by a callback although
> there is an other i2c transfer running. In this case do not interrupt the
> transfer and return with an error.
> 
> Signed-off-by: Gerald Loacker <gerald.loacker@wolfvision.net>
> ---
>  drivers/i2c/busses/i2c-rockchip.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/busses/i2c-rockchip.c b/drivers/i2c/busses/i2c-rockchip.c
> index 1bca3e9913..a869b9d0b7 100644
> --- a/drivers/i2c/busses/i2c-rockchip.c
> +++ b/drivers/i2c/busses/i2c-rockchip.c
> @@ -369,7 +369,19 @@ static int rockchip_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
>  {
>  	struct rk_i2c *i2c = to_rk_i2c(adapter);
>  	struct device *dev = &adapter->dev;
> -	int i, ret = 0;
> +	struct i2c_regs *regs = i2c->regs;
> +	int i, ret = 0, val;
> +
> +	val = readl(&regs->con);
> +	if (val & I2C_CON_EN) {
> +		val = readl(&regs->con);
> +		if (val & I2C_IPD_ALL_CLEAN) {
> +			dev_dbg(dev,
> +				"i2c_xfer: %d messages dropped due to pending interrupts\n",
> +				nmsgs);
> +			return -EAGAIN;
> +		}
> +	}

Can you have a look how this can happen? Normally this should only
happen if you have a heartbeat LED behind a I2C GPIO expander or some
other unusual setup. Adding a dump_stack() next to the dev_dbg() call
might give a clue.

Let's see how this really happens, but generally I think we should find
another solution for this, either on I2C core level or by replacing
the readl_poll_timeout() with a variant that doesn't allow running in
the background, i.e. one which uses is_timeout_non_interruptible()
rather than is_timeout().

Sascha

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