Re: [PATCH v4 04/18] mux: add mux_chip_resume() function

Peter Rosin
2024-09-03T13:17:20Z

Hi!

Sorry for being unresponsive.

2024-03-04 at 16:35, Thomas Richard wrote:
> The mux_chip_resume() function restores a mux_chip using the cached state
> of each mux.
>
> Signed-off-by: Thomas Richard <thomas.richard@bootlin.com>
> ---
> drivers/mux/core.c | 29 +++++++++++++++++++++++++++++
> include/linux/mux/driver.h | 1 +
> 2 files changed, 30 insertions(+)
>
> diff --git a/drivers/mux/core.c b/drivers/mux/core.c
> index 775816112932..0742aa2a7c73 100644
> --- a/drivers/mux/core.c
> +++ b/drivers/mux/core.c
> @@ -215,6 +215,35 @@ void mux_chip_free(struct mux_chip *mux_chip)
> }
> EXPORT_SYMBOL_GPL(mux_chip_free);
>
> +/**
> + * mux_chip_resume() - restores the mux-chip state
> + * @mux_chip: The mux-chip to resume.
> + *
> + * Restores the mux-chip state.
> + *
> + * Return: Zero on success or a negative errno on error.
> + */
> +int mux_chip_resume(struct mux_chip *mux_chip)
> +{
> + int ret, i;
> +
> + for (i = 0; i < mux_chip->controllers; ++i) {
> + struct mux_control *mux = &mux_chip->mux[i];
> +
> + if (mux->cached_state == MUX_CACHE_UNKNOWN)
> + continue;
> +
> + ret = mux_control_set(mux, mux->cached_state);

mux_control_set() is an internal helper. It is called from
__mux_control_select() and mux_control_deselect() (and on init...)

In all those cases, there is no race to reach the mux_control_set()
function, by means of the mux->lock semaphore (or the mux not being
"published" yet).

I fail to see how resume is safe when mux->lock is ignored?

Cheers,
Peter

> + if (ret < 0) {
> + dev_err(&mux_chip->dev, "unable to restore state\n");
> + return ret;
> + }
> + }
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(mux_chip_resume);
> +
> static void devm_mux_chip_release(struct device *dev, void *res)
> {
> struct mux_chip *mux_chip = *(struct mux_chip **)res;
> diff --git a/include/linux/mux/driver.h b/include/linux/mux/driver.h
> index 18824064f8c0..2a7e5ec5d540 100644
> --- a/include/linux/mux/driver.h
> +++ b/include/linux/mux/driver.h
> @@ -88,6 +88,7 @@ struct mux_chip *mux_chip_alloc(struct device *dev,
> int mux_chip_register(struct mux_chip *mux_chip);
> void mux_chip_unregister(struct mux_chip *mux_chip);
> void mux_chip_free(struct mux_chip *mux_chip);
> +int mux_chip_resume(struct mux_chip *mux_chip);
>
> struct mux_chip *devm_mux_chip_alloc(struct device *dev,
> unsigned int controllers,
>