[PATCH v1] i2c: lpi2c: implement master_xfer_atomic callback

[Andi Shyti]

Hi Francesco,

I'm sorry for the late reply on this.

Can someone from NXP help with the review? Carlos? Dong?

On Wed, Mar 19, 2025 at 03:51:14PM +0100, Francesco Dolcini wrote:
> From: Emanuele Ghidoli <emanuele.ghidoli at toradex.com>
> 
> Rework the read and write code paths in the driver to support operation
> in atomic contexts. To achieve this, the driver must not rely on IRQs
> or perform any scheduling, e.g., via a sleep or schedule routine. Even
> jiffies do not advance in atomic contexts, so timeouts based on them
> are substituted with delays.
> 
> Implement atomic, sleep-free, and IRQ-less operation. This increases
> complexity but is necessary for atomic I2C transfers required by some
> hardware configurations, e.g., to trigger reboots on an external PMIC chip.
> 
> Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli at toradex.com>
> Signed-off-by: Francesco Dolcini <francesco.dolcini at toradex.com>
> ---
>  drivers/i2c/busses/i2c-imx-lpi2c.c | 258 +++++++++++++++++++----------
>  1 file changed, 173 insertions(+), 85 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c b/drivers/i2c/busses/i2c-imx-lpi2c.c
> index 0d4b3935e687..f34b6f07e9a4 100644
> --- a/drivers/i2c/busses/i2c-imx-lpi2c.c
> +++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
> @@ -16,6 +16,7 @@
>  #include <linux/init.h>
>  #include <linux/interrupt.h>
>  #include <linux/io.h>
> +#include <linux/iopoll.h>
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> @@ -187,36 +188,35 @@ struct lpi2c_imx_struct {
>  	struct i2c_client	*target;
>  };
>  
> +#define READL_POLL_TIMEOUT(atomic, addr, val, cond, delay_us, timeout_us) \

READ_POLL_TIMEOUT is not really a name that belongs to this
driver. Could we name it something like
lpi2c_imx_read_poll_timeout()? I'd prefer lowercase, but I
won't object to capital letters.

Additionally, the timeout_us value is always 500000, could we
just drop it from the parameter list? Same goes for LPI2C_MSR.

Thanks,
Andi