[PATCH v2 3/4] usb: typec: mux: add typec orientation switch support via mux controller

[Heikki Krogerus]

Hi,

On Wed, Aug 24, 2022 at 03:54:28AM +0800, Xu Yang wrote:
> Some dedicated mux block can use existing mux controller as a mux
> provider, typec port as a consumer to select channel for orientation
> switch, this can be an alternate way to control typec orientation switch.
> Also, one mux controller could cover highspeed, superspeed and sideband
> use case one time in this implementation.
> 
> Reported-by: kernel test robot <lkp at intel.com>

Drop that Reported-by tag.

> Signed-off-by: Xu Yang <xu.yang_2 at nxp.com>
> 
> ---
> Changes since v1:
> - add build dependence (select MULTIPLEXER)
> - improve Multiplexer control logic
> 
>  drivers/usb/typec/Kconfig     |  1 +
>  drivers/usb/typec/mux.c       | 76 ++++++++++++++++++++++++++++++++++-
>  include/linux/usb/typec_mux.h |  7 +---
>  3 files changed, 78 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/usb/typec/Kconfig b/drivers/usb/typec/Kconfig
> index 5defdfead653..73d4976d8148 100644
> --- a/drivers/usb/typec/Kconfig
> +++ b/drivers/usb/typec/Kconfig
> @@ -2,6 +2,7 @@
>  
>  menuconfig TYPEC
>  	tristate "USB Type-C Support"
> +	select MULTIPLEXER

Whoa, do not tie TYPEC to another subsystem like that! You probable
want to make your driver depend on that instead.

>  	help
>  	  USB Type-C Specification defines a cable and connector for USB where
>  	  only one type of plug is supported on both ends, i.e. there will not
> diff --git a/drivers/usb/typec/mux.c b/drivers/usb/typec/mux.c
> index 464330776cd6..05e6ed217620 100644
> --- a/drivers/usb/typec/mux.c
> +++ b/drivers/usb/typec/mux.c
> @@ -13,6 +13,7 @@
>  #include <linux/mutex.h>
>  #include <linux/property.h>
>  #include <linux/slab.h>
> +#include <linux/mux/consumer.h>
>  
>  #include "class.h"
>  #include "mux.h"
> @@ -22,6 +23,11 @@
>  struct typec_switch {
>  	struct typec_switch_dev *sw_devs[TYPEC_MUX_MAX_DEVS];
>  	unsigned int num_sw_devs;
> +
> +	/* Could handle HighSpeed, SuperSpeed, Sideband switch one time */
> +	struct mux_control *mux_switch;

That does not belong here...

> +	/* 3 state correspond to NONE, NORMAL, REVERSE for all switches */
> +	int mux_states[3];
>  };
>  
>  static int switch_fwnode_match(struct device *dev, const void *fwnode)
> @@ -117,6 +123,58 @@ struct typec_switch *fwnode_typec_switch_get(struct fwnode_handle *fwnode)
>  }
>  EXPORT_SYMBOL_GPL(fwnode_typec_switch_get);
>  
> +static struct typec_switch *mux_control_typec_switch_get(struct device *dev)
> +{
> +	struct typec_switch *sw;
> +	struct mux_control *mux;
> +	int ret;
> +
> +	if (!device_property_present(dev, "mux-controls"))
> +		return NULL;
> +
> +	sw = kzalloc(sizeof(*sw), GFP_KERNEL);
> +	if (!sw)
> +		return ERR_PTR(-ENOMEM);
> +
> +	mux = mux_control_get(dev, NULL);
> +	if (!IS_ERR(mux)) {
> +		sw->mux_switch = mux;
> +		ret = device_property_read_u32_array(dev,
> +			"typec-switch-states", sw->mux_states, 3);
> +		if (ret) {
> +			kfree(sw);
> +			return ERR_PTR(ret);
> +		}
> +	} else {
> +		kfree(sw);
> +		return ERR_CAST(mux);
> +	}
> +
> +	return sw;
> +}

That code is broken - you return a switch that has never been
registered - but never mind that...

You need to register the switch from the place/driver that actually
handles the orientation. If you really think that you have to have a
generic multiplexer class wrapper layer for these switches, then you
need to propose a multiplexer class wrapper driver for that. Though,
I'm not sure you need that.

There is a GPIO driver proposal for these switches, so can you take a
look if that covers your case as well:
https://lore.kernel.org/linux-usb/20220810204750.3672362-3-bjorn.andersson@linaro.org/#t

In any case, you can't mix that code into the device class code itself
like you do above. That kind of coupling is always going to be fragile
(as we can see above), but more importantly, it forces the dependency
on every Type-C driver, and that is completely wrong.

So please keep the subsystems themselves independent of each other and
handle things in the device drivers.

thanks,

-- 
heikki