Date:   Thu, 30 Jun 2022 11:17:59 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Prashant Malani <pmalani@...omium.org>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        chrome-platform@...ts.linux.dev, bleung@...omium.org,
        Daisuke Nojiri <dnojiri@...omium.org>,
        "Dustin L. Howett" <dustin@...ett.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guenter Roeck <groeck@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Sebastian Reichel <sebastian.reichel@...labora.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH 1/9] usb: typec: Add support for retimers

On Wed, Jun 29, 2022 at 11:32:19PM +0000, Prashant Malani wrote:
> Introduce a retimer device class and associated functions that register
> and use retimer "switch" devices. These operate in a manner similar to
> the "mode-switch" and help configure retimers that exist between the
> Type-C connector and host controller(s).
> 
> Type C ports can be linked to retimers using firmware node device
> references (again, in a manner similar to "mode-switch").
> 
> Signed-off-by: Prashant Malani <pmalani@...omium.org>

Cool! This looks really good to me.

I'll add Mika here, just to keep him in the loop. Thunderbolt/USB4 can
control the same physical retimers over the SBU line. Right now there
is no conflict, but I think we want to later be able to use these
devices to upgrade the retimer firmware, and that is something that
the Thunderbolt/USB4 already does. So let's keep an eye on this.

I wonder, would it make sense to later make the thunderbolt_retimer
devices also part of the device class that's introduced here? I think
that way it would be easier to later figure out which
thunderbolt_retimer and which retimer_switch represent the same
physical retimer. And perhaps it would also be more clear for the user
space to have a single device class for the retimers?

Maybe the device class could be named just "retimer", and the device
type could then be named "typec_retimer" instead of "retimer_switch"?

thanks,

> ---
>  drivers/usb/typec/Makefile        |   2 +-
>  drivers/usb/typec/class.c         |   9 +-
>  drivers/usb/typec/class.h         |   1 +
>  drivers/usb/typec/retimer.c       | 168 ++++++++++++++++++++++++++++++
>  drivers/usb/typec/retimer.h       |  15 +++
>  include/linux/usb/typec_retimer.h |  45 ++++++++
>  6 files changed, 238 insertions(+), 2 deletions(-)
>  create mode 100644 drivers/usb/typec/retimer.c
>  create mode 100644 drivers/usb/typec/retimer.h
>  create mode 100644 include/linux/usb/typec_retimer.h
> 
> diff --git a/drivers/usb/typec/Makefile b/drivers/usb/typec/Makefile
> index 2f174cd3e5df..4955d9af0811 100644
> --- a/drivers/usb/typec/Makefile
> +++ b/drivers/usb/typec/Makefile
> @@ -1,6 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0
>  obj-$(CONFIG_TYPEC)		+= typec.o
> -typec-y				:= class.o mux.o bus.o pd.o
> +typec-y				:= class.o mux.o bus.o pd.o retimer.o
>  typec-$(CONFIG_ACPI)		+= port-mapper.o
>  obj-$(CONFIG_TYPEC)		+= altmodes/
>  obj-$(CONFIG_TYPEC_TCPM)	+= tcpm/
> diff --git a/drivers/usb/typec/class.c b/drivers/usb/typec/class.c
> index bbc46b14f99a..2fa0b3718d23 100644
> --- a/drivers/usb/typec/class.c
> +++ b/drivers/usb/typec/class.c
> @@ -2299,10 +2299,14 @@ static int __init typec_init(void)
>  	if (ret)
>  		goto err_unregister_bus;
>  
> -	ret = class_register(&typec_class);
> +	ret = class_register(&typec_retimer_class);
>  	if (ret)
>  		goto err_unregister_mux_class;
>  
> +	ret = class_register(&typec_class);
> +	if (ret)
> +		goto err_unregister_retimer_class;
> +
>  	ret = usb_power_delivery_init();
>  	if (ret)
>  		goto err_unregister_class;
> @@ -2312,6 +2316,9 @@ static int __init typec_init(void)
>  err_unregister_class:
>  	class_unregister(&typec_class);
>  
> +err_unregister_retimer_class:
> +	class_unregister(&typec_retimer_class);
> +
>  err_unregister_mux_class:
>  	class_unregister(&typec_mux_class);
>  
> diff --git a/drivers/usb/typec/class.h b/drivers/usb/typec/class.h
> index b531f9853bc0..1bb1da124109 100644
> --- a/drivers/usb/typec/class.h
> +++ b/drivers/usb/typec/class.h
> @@ -76,6 +76,7 @@ extern const struct device_type typec_port_dev_type;
>  #define is_typec_port(dev) ((dev)->type == &typec_port_dev_type)
>  
>  extern struct class typec_mux_class;
> +extern struct class typec_retimer_class;
>  extern struct class typec_class;
>  
>  #if defined(CONFIG_ACPI)
> diff --git a/drivers/usb/typec/retimer.c b/drivers/usb/typec/retimer.c
> new file mode 100644
> index 000000000000..2fa0aeb9363c
> --- /dev/null
> +++ b/drivers/usb/typec/retimer.c
> @@ -0,0 +1,168 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright 2022 Google LLC
> + *
> + * USB Type-C Retimer support.
> + * Author: Prashant Malani <pmalani@...omium.org>
> + *
> + */
> +
> +#include <linux/device.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/property.h>
> +#include <linux/slab.h>
> +
> +#include "class.h"
> +#include "retimer.h"
> +
> +static bool dev_name_ends_with(struct device *dev, const char *suffix)
> +{
> +	const char *name = dev_name(dev);
> +	const int name_len = strlen(name);
> +	const int suffix_len = strlen(suffix);
> +
> +	if (suffix_len > name_len)
> +		return false;
> +
> +	return strcmp(name + (name_len - suffix_len), suffix) == 0;
> +}
> +
> +static int retimer_fwnode_match(struct device *dev, const void *fwnode)
> +{
> +	return dev_fwnode(dev) == fwnode && dev_name_ends_with(dev, "-retimer");
> +}
> +
> +static void *typec_retimer_match(struct fwnode_handle *fwnode, const char *id, void *data)
> +{
> +	struct device *dev  = class_find_device(&typec_retimer_class, NULL, fwnode,
> +						retimer_fwnode_match);
> +
> +	return dev ? to_typec_retimer(dev) : ERR_PTR(-EPROBE_DEFER);
> +}
> +
> +/**
> + * fwnode_typec_retimer_get - Find USB Type-C retimer.
> + * @fwnode: The caller device node.
> + *
> + * Finds a retimer linked to the caller. This function is primarily meant for the
> + * Type-C drivers. Returns a reference to the retimer on success, NULL if no
> + * matching connection was found, or ERR_PTR(-EPROBE_DEFER) when a connection
> + * was found but the retimer has not been enumerated yet.
> + */
> +struct typec_retimer *fwnode_typec_retimer_get(struct fwnode_handle *fwnode)
> +{
> +	struct typec_retimer *retimer;
> +
> +	retimer = fwnode_connection_find_match(fwnode, "retimer-switch", NULL, typec_retimer_match);
> +	if (!IS_ERR_OR_NULL(retimer))
> +		WARN_ON(!try_module_get(retimer->dev.parent->driver->owner));
> +
> +	return retimer;
> +}
> +EXPORT_SYMBOL_GPL(fwnode_typec_retimer_get);
> +
> +/**
> + * typec_retimer_put - Release handle to a retimer.
> + * @retimer: USB Type-C Connector Retimer.
> + *
> + * Decrements reference count for @retimer.
> + */
> +void typec_retimer_put(struct typec_retimer *retimer)
> +{
> +	if (!IS_ERR_OR_NULL(retimer)) {
> +		module_put(retimer->dev.parent->driver->owner);
> +		put_device(&retimer->dev);
> +	}
> +}
> +EXPORT_SYMBOL_GPL(typec_retimer_put);
> +
> +int typec_retimer_set(struct typec_retimer *retimer, struct typec_retimer_state *state)
> +{
> +	if (IS_ERR_OR_NULL(retimer))
> +		return 0;
> +
> +	return retimer->set(retimer, state);
> +}
> +EXPORT_SYMBOL_GPL(typec_retimer_set);
> +
> +static void typec_retimer_release(struct device *dev)
> +{
> +	kfree(to_typec_retimer(dev));
> +}
> +
> +static const struct device_type typec_retimer_dev_type = {
> +	.name = "retimer_switch",
> +	.release = typec_retimer_release,
> +};
> +
> +/**
> + * typec_retimer_register - Register a retimer device.
> + * @parent: Parent device.
> + * @desc: Retimer description.
> + *
> + * Some USB Type-C connectors have their physical lines routed through retimers before they
> + * reach muxes or host controllers. In some cases (for example: using alternate modes)
> + * these retimers need to be reconfigured appropriately. This function registers retimer
> + * switches which route and potentially modify the signals on the Type C physical lines
> + * enroute to the host controllers.
> + */
> +struct typec_retimer *
> +typec_retimer_register(struct device *parent, const struct typec_retimer_desc *desc)
> +{
> +	struct typec_retimer *retimer;
> +	int ret;
> +
> +	if (!desc || !desc->set)
> +		return ERR_PTR(-EINVAL);
> +
> +	retimer = kzalloc(sizeof(*retimer), GFP_KERNEL);
> +	if (!retimer)
> +		return ERR_PTR(-ENOMEM);
> +
> +	retimer->set = desc->set;
> +
> +	device_initialize(&retimer->dev);
> +	retimer->dev.parent = parent;
> +	retimer->dev.fwnode = desc->fwnode;
> +	retimer->dev.class = &typec_retimer_class;
> +	retimer->dev.type = &typec_retimer_dev_type;
> +	retimer->dev.driver_data = desc->drvdata;
> +	dev_set_name(&retimer->dev, "%s-retimer",
> +		     desc->name ? desc->name : dev_name(parent));
> +
> +	ret = device_add(&retimer->dev);
> +	if (ret) {
> +		dev_err(parent, "failed to register retimer (%d)\n", ret);
> +		put_device(&retimer->dev);
> +		return ERR_PTR(ret);
> +	}
> +
> +	return retimer;
> +}
> +EXPORT_SYMBOL_GPL(typec_retimer_register);
> +
> +/**
> + * typec_retimer_unregister - Unregister retimer device.
> + * @retimer: USB Type-C Connector retimer.
> + *
> + * Unregister retimer that was registered with typec_retimer_register().
> + */
> +void typec_retimer_unregister(struct typec_retimer *retimer)
> +{
> +	if (!IS_ERR_OR_NULL(retimer))
> +		device_unregister(&retimer->dev);
> +}
> +EXPORT_SYMBOL_GPL(typec_retimer_unregister);
> +
> +void *typec_retimer_get_drvdata(struct typec_retimer *retimer)
> +{
> +	return dev_get_drvdata(&retimer->dev);
> +}
> +EXPORT_SYMBOL_GPL(typec_retimer_get_drvdata);
> +
> +struct class typec_retimer_class = {
> +	.name = "typec_retimer",
> +	.owner = THIS_MODULE,
> +};
> diff --git a/drivers/usb/typec/retimer.h b/drivers/usb/typec/retimer.h
> new file mode 100644
> index 000000000000..fa15951d4846
> --- /dev/null
> +++ b/drivers/usb/typec/retimer.h
> @@ -0,0 +1,15 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef __USB_TYPEC_RETIMER__
> +#define __USB_TYPEC_RETIMER__
> +
> +#include <linux/usb/typec_retimer.h>
> +
> +struct typec_retimer {
> +	struct device dev;
> +	typec_retimer_set_fn_t set;
> +};
> +
> +#define to_typec_retimer(_dev_) container_of(_dev_, struct typec_retimer, dev)
> +
> +#endif /* __USB_TYPEC_RETIMER__ */
> diff --git a/include/linux/usb/typec_retimer.h b/include/linux/usb/typec_retimer.h
> new file mode 100644
> index 000000000000..5e036b3360e2
> --- /dev/null
> +++ b/include/linux/usb/typec_retimer.h
> @@ -0,0 +1,45 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef __USB_TYPEC_RETIMER
> +#define __USB_TYPEC_RETIMER
> +
> +#include <linux/property.h>
> +#include <linux/usb/typec.h>
> +
> +struct device;
> +struct typec_retimer;
> +struct typec_altmode;
> +struct fwnode_handle;
> +
> +struct typec_retimer_state {
> +	struct typec_altmode *alt;
> +	unsigned long mode;
> +	void *data;
> +};
> +
> +typedef int (*typec_retimer_set_fn_t)(struct typec_retimer *retimer,
> +				      struct typec_retimer_state *state);
> +
> +struct typec_retimer_desc {
> +	struct fwnode_handle *fwnode;
> +	typec_retimer_set_fn_t set;
> +	const char *name;
> +	void *drvdata;
> +};
> +
> +struct typec_retimer *fwnode_typec_retimer_get(struct fwnode_handle *fwnode);
> +void typec_retimer_put(struct typec_retimer *retimer);
> +int typec_retimer_set(struct typec_retimer *retimer, struct typec_retimer_state *state);
> +
> +static inline struct typec_retimer *typec_retimer_get(struct device *dev)
> +{
> +	return fwnode_typec_retimer_get(dev_fwnode(dev));
> +}
> +
> +struct typec_retimer *
> +typec_retimer_register(struct device *parent, const struct typec_retimer_desc *desc);
> +void typec_retimer_unregister(struct typec_retimer *retimer);
> +
> +void *typec_retimer_get_drvdata(struct typec_retimer *retimer);
> +
> +#endif /* __USB_TYPEC_RETIMER */
> -- 
> 2.37.0.rc0.161.g10f37bed90-goog

-- 
heikki

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