Date:   Mon, 11 Jul 2022 12:42:29 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Sean Anderson <sean.anderson@...o.com>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>,
        Madalin Bucur <madalin.bucur@....com>,
        "David S . Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        Andrew Lunn <andrew@...n.ch>,
        Frank Rowand <frowand.list@...il.com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org
Subject: Re: [RFC PATCH net-next 3/9] net: pcs: Add helpers for registering
 and finding PCSs

On Mon, Jul 11, 2022 at 9:05 AM Sean Anderson <sean.anderson@...o.com> wrote:
>
> This adds support for getting PCS devices from the device tree. PCS
> drivers must first register with phylink_register_pcs. After that, MAC
> drivers may look up their PCS using phylink_get_pcs.
>
> To prevent the PCS driver from leaving suddenly, we use try_module_get. To
> provide some ordering during probing/removal, we use device links managed
> by of_fwnode_add_links. This will reduce the number of probe failures due
> to deferral. It will not prevent this for non-standard properties (aka
> pcsphy-handle), but the worst that happens is that we re-probe a few times.
>
> At the moment there is no support for specifying the interface used to
> talk to the PCS. The MAC driver is expected to know how to talk to the
> PCS. This is not a change, but it is perhaps an area for improvement.
>
> Signed-off-by: Sean Anderson <sean.anderson@...o.com>
> ---
> This is adapted from [1], primarily incorporating the changes discussed
> there.
>
> [1] https://lore.kernel.org/netdev/9f73bc4f-5f99-95f5-78fa-dac96f9e0146@seco.com/
>
>  MAINTAINERS              |   1 +
>  drivers/net/pcs/Kconfig  |  12 +++
>  drivers/net/pcs/Makefile |   2 +
>  drivers/net/pcs/core.c   | 226 +++++++++++++++++++++++++++++++++++++++
>  drivers/of/property.c    |   2 +
>  include/linux/pcs.h      |  33 ++++++
>  include/linux/phylink.h  |   6 ++
>  7 files changed, 282 insertions(+)
>  create mode 100644 drivers/net/pcs/core.c
>  create mode 100644 include/linux/pcs.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index ca95b1833b97..3965d49753d3 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -7450,6 +7450,7 @@ F:        include/linux/*mdio*.h
>  F:     include/linux/mdio/*.h
>  F:     include/linux/mii.h
>  F:     include/linux/of_net.h
> +F:     include/linux/pcs.h
>  F:     include/linux/phy.h
>  F:     include/linux/phy_fixed.h
>  F:     include/linux/platform_data/mdio-bcm-unimac.h
> diff --git a/drivers/net/pcs/Kconfig b/drivers/net/pcs/Kconfig
> index 22ba7b0b476d..fed6264fdf33 100644
> --- a/drivers/net/pcs/Kconfig
> +++ b/drivers/net/pcs/Kconfig
> @@ -5,6 +5,18 @@
>
>  menu "PCS device drivers"
>
> +config PCS
> +       bool "PCS subsystem"
> +       help
> +         This provides common helper functions for registering and looking up
> +         Physical Coding Sublayer (PCS) devices. PCS devices translate between
> +         different interface types. In some use cases, they may either
> +         translate between different types of Medium-Independent Interfaces
> +         (MIIs), such as translating GMII to SGMII. This allows using a fast
> +         serial interface to talk to the phy which translates the MII to the
> +         Medium-Dependent Interface. Alternatively, they may translate a MII
> +         directly to an MDI, such as translating GMII to 1000Base-X.
> +
>  config PCS_XPCS
>         tristate "Synopsys DesignWare XPCS controller"
>         depends on MDIO_DEVICE && MDIO_BUS
> diff --git a/drivers/net/pcs/Makefile b/drivers/net/pcs/Makefile
> index 0603d469bd57..1fd21a1619d4 100644
> --- a/drivers/net/pcs/Makefile
> +++ b/drivers/net/pcs/Makefile
> @@ -1,6 +1,8 @@
>  # SPDX-License-Identifier: GPL-2.0
>  # Makefile for Linux PCS drivers
>
> +obj-$(CONFIG_PCS)              += core.o
> +
>  pcs_xpcs-$(CONFIG_PCS_XPCS)    := pcs-xpcs.o pcs-xpcs-nxp.o
>
>  obj-$(CONFIG_PCS_XPCS)         += pcs_xpcs.o
> diff --git a/drivers/net/pcs/core.c b/drivers/net/pcs/core.c
> new file mode 100644
> index 000000000000..b39ff1ccdb34
> --- /dev/null
> +++ b/drivers/net/pcs/core.c
> @@ -0,0 +1,226 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2022 Sean Anderson <sean.anderson@...o.com>
> + */
> +
> +#include <linux/fwnode.h>
> +#include <linux/list.h>
> +#include <linux/mutex.h>
> +#include <linux/pcs.h>
> +#include <linux/phylink.h>
> +#include <linux/property.h>
> +
> +static LIST_HEAD(pcs_devices);
> +static DEFINE_MUTEX(pcs_mutex);
> +
> +/**
> + * pcs_register() - register a new PCS
> + * @pcs: the PCS to register
> + *
> + * Registers a new PCS which can be automatically attached to a phylink.
> + *
> + * Return: 0 on success, or -errno on error
> + */
> +int pcs_register(struct phylink_pcs *pcs)
> +{
> +       if (!pcs->dev || !pcs->ops)
> +               return -EINVAL;
> +       if (!pcs->ops->pcs_an_restart || !pcs->ops->pcs_config ||
> +           !pcs->ops->pcs_get_state)
> +               return -EINVAL;
> +
> +       INIT_LIST_HEAD(&pcs->list);
> +       mutex_lock(&pcs_mutex);
> +       list_add(&pcs->list, &pcs_devices);
> +       mutex_unlock(&pcs_mutex);
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(pcs_register);
> +
> +/**
> + * pcs_unregister() - unregister a PCS
> + * @pcs: a PCS previously registered with pcs_register()
> + */
> +void pcs_unregister(struct phylink_pcs *pcs)
> +{
> +       mutex_lock(&pcs_mutex);
> +       list_del(&pcs->list);
> +       mutex_unlock(&pcs_mutex);
> +}
> +EXPORT_SYMBOL_GPL(pcs_unregister);
> +
> +static void devm_pcs_release(struct device *dev, void *res)
> +{
> +       pcs_unregister(*(struct phylink_pcs **)res);
> +}
> +
> +/**
> + * devm_pcs_register - resource managed pcs_register()
> + * @dev: device that is registering this PCS
> + * @pcs: the PCS to register
> + *
> + * Managed pcs_register(). For PCSs registered by this function,
> + * pcs_unregister() is automatically called on driver detach. See
> + * pcs_register() for more information.
> + *
> + * Return: 0 on success, or -errno on failure
> + */
> +int devm_pcs_register(struct device *dev, struct phylink_pcs *pcs)
> +{
> +       struct phylink_pcs **pcsp;
> +       int ret;
> +
> +       pcsp = devres_alloc(devm_pcs_release, sizeof(*pcsp),
> +                           GFP_KERNEL);
> +       if (!pcsp)
> +               return -ENOMEM;
> +
> +       ret = pcs_register(pcs);
> +       if (ret) {
> +               devres_free(pcsp);
> +               return ret;
> +       }
> +
> +       *pcsp = pcs;
> +       devres_add(dev, pcsp);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(devm_pcs_register);
> +
> +/**
> + * pcs_find() - Find the PCS associated with a fwnode or device
> + * @fwnode: The PCS's fwnode
> + * @dev: The PCS's device
> + *
> + * Search PCSs registered with pcs_register() for one with a matching
> + * fwnode or device. Either @fwnode or @dev may be %NULL if matching against a
> + * fwnode or device is not desired (respectively).
> + *
> + * Return: a matching PCS, or %NULL if not found
> + */
> +static struct phylink_pcs *pcs_find(const struct fwnode_handle *fwnode,
> +                                   const struct device *dev)
> +{
> +       struct phylink_pcs *pcs;
> +
> +       mutex_lock(&pcs_mutex);
> +       list_for_each_entry(pcs, &pcs_devices, list) {
> +               if (dev && pcs->dev == dev)
> +                       goto out;
> +               if (fwnode && pcs->dev->fwnode == fwnode)
> +                       goto out;
> +       }
> +       pcs = NULL;
> +
> +out:
> +       mutex_unlock(&pcs_mutex);
> +       pr_devel("%s: looking for %pfwf or %s %s...%s found\n", __func__,
> +                fwnode, dev ? dev_driver_string(dev) : "(null)",
> +                dev ? dev_name(dev) : "(null)", pcs ? " not" : "");
> +       return pcs;
> +}
> +
> +/**
> + * pcs_get_tail() - Finish getting a PCS
> + * @pcs: The PCS to get, or %NULL if one could not be found
> + *
> + * This performs common operations necessary when getting a PCS (chiefly
> + * incrementing reference counts)
> + *
> + * Return: @pcs, or an error pointer on failure
> + */
> +static struct phylink_pcs *pcs_get_tail(struct phylink_pcs *pcs)
> +{
> +       if (!pcs)
> +               return ERR_PTR(-EPROBE_DEFER);
> +
> +       if (!try_module_get(pcs->ops->owner))
> +               return ERR_PTR(-ENODEV);
> +       get_device(pcs->dev);
> +
> +       return pcs;
> +}
> +
> +/**
> + * _pcs_get_by_fwnode() - Get a PCS from a fwnode property
> + * @fwnode: The fwnode to get an associated PCS of
> + * @id: The name of the PCS to get. May be %NULL to get the first PCS.
> + * @optional: Whether the PCS is optional or not
> + *
> + * Look up a PCS associated with @fwnode and return a reference to it. Every
> + * call to pcs_get_by_fwnode() must be balanced with one to pcs_put().
> + *
> + * If @optional is true, and @id is non-%NULL, then if @id cannot be found in
> + * pcs-names, %NULL is returned (instead of an error). If @optional is true and
> + * @id is %NULL, then no error is returned if pcs-handle is absent.
> + *
> + * Return: a PCS if found, or an error pointer on failure
> + */
> +struct phylink_pcs *_pcs_get_by_fwnode(const struct fwnode_handle *fwnode,
> +                                      const char *id, bool optional)
> +{
> +       int index;
> +       struct phylink_pcs *pcs;
> +       struct fwnode_handle *pcs_fwnode;
> +
> +       if (id)
> +               index = fwnode_property_match_string(fwnode, "pcs-names", id);
> +       else
> +               index = 0;
> +       if (index < 0) {
> +               if (optional && (index == -EINVAL || index == -ENODATA))
> +                       return NULL;
> +               return ERR_PTR(index);
> +       }
> +
> +       /* First try pcs-handle, and if that doesn't work fall back to the
> +        * (legacy) pcsphy-handle.
> +        */
> +       pcs_fwnode = fwnode_find_reference(fwnode, "pcs-handle", index);
> +       if (PTR_ERR(pcs_fwnode) == -ENOENT)
> +               pcs_fwnode = fwnode_find_reference(fwnode, "pcsphy-handle",
> +                                                  index);
> +       if (optional && !id && PTR_ERR(pcs_fwnode) == -ENOENT)
> +               return NULL;
> +       else if (IS_ERR(pcs_fwnode))
> +               return ERR_CAST(pcs_fwnode);
> +
> +       pcs = pcs_find(pcs_fwnode, NULL);
> +       fwnode_handle_put(pcs_fwnode);
> +       return pcs_get_tail(pcs);
> +}
> +EXPORT_SYMBOL_GPL(pcs_get_by_fwnode);
> +
> +/**
> + * pcs_get_by_provider() - Get a PCS from an existing provider
> + * @dev: The device providing the PCS
> + *
> + * This finds the first PCS registersed by @dev and returns a reference to it.
> + * Every call to pcs_get_by_provider() must be balanced with one to
> + * pcs_put().
> + *
> + * Return: a PCS if found, or an error pointer on failure
> + */
> +struct phylink_pcs *pcs_get_by_provider(const struct device *dev)
> +{
> +       return pcs_get_tail(pcs_find(NULL, dev));
> +}
> +EXPORT_SYMBOL_GPL(pcs_get_by_provider);
> +
> +/**
> + * pcs_put() - Release a previously-acquired PCS
> + * @pcs: The PCS to put
> + *
> + * This frees resources associated with the PCS which were acquired when it was
> + * gotten.
> + */
> +void pcs_put(struct phylink_pcs *pcs)
> +{
> +       if (!pcs)
> +               return;
> +
> +       put_device(pcs->dev);
> +       module_put(pcs->ops->owner);
> +}
> +EXPORT_SYMBOL_GPL(pcs_put);
> diff --git a/drivers/of/property.c b/drivers/of/property.c
> index 967f79b59016..860d35bde5e9 100644
> --- a/drivers/of/property.c
> +++ b/drivers/of/property.c
> @@ -1318,6 +1318,7 @@ DEFINE_SIMPLE_PROP(pinctrl6, "pinctrl-6", NULL)
>  DEFINE_SIMPLE_PROP(pinctrl7, "pinctrl-7", NULL)
>  DEFINE_SIMPLE_PROP(pinctrl8, "pinctrl-8", NULL)
>  DEFINE_SIMPLE_PROP(remote_endpoint, "remote-endpoint", NULL)
> +DEFINE_SIMPLE_PROP(pcs_handle, "pcs-handle", NULL)
>  DEFINE_SIMPLE_PROP(pwms, "pwms", "#pwm-cells")
>  DEFINE_SIMPLE_PROP(resets, "resets", "#reset-cells")
>  DEFINE_SIMPLE_PROP(leds, "leds", NULL)
> @@ -1406,6 +1407,7 @@ static const struct supplier_bindings of_supplier_bindings[] = {
>         { .parse_prop = parse_pinctrl7, },
>         { .parse_prop = parse_pinctrl8, },
>         { .parse_prop = parse_remote_endpoint, .node_not_dev = true, },
> +       { .parse_prop = parse_pcs_handle, },
>         { .parse_prop = parse_pwms, },
>         { .parse_prop = parse_resets, },
>         { .parse_prop = parse_leds, },

Can you break the changes to this file into a separate patch please?
That'll clarify that this doesn't depend on any of the other changes
in this patch to work and it can stand on its own.

Also, I don't know how the pcs-handle is used, but it's likely that
this probe ordering enforcement could cause issues. So, if we need to
revert it, having it as a separate patch would help too.

And put this at the end of the series maybe?

Thanks,
Saravana

>
> diff --git a/include/linux/pcs.h b/include/linux/pcs.h
> new file mode 100644
> index 000000000000..00e76594e03c
> --- /dev/null
> +++ b/include/linux/pcs.h
> @@ -0,0 +1,33 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2022 Sean Anderson <sean.anderson@...o.com>
> + */
> +
> +#ifndef _PCS_H
> +#define _PCS_H
> +
> +struct phylink_pcs;
> +struct fwnode;
> +
> +int pcs_register(struct phylink_pcs *pcs);
> +void pcs_unregister(struct phylink_pcs *pcs);
> +int devm_pcs_register(struct device *dev, struct phylink_pcs *pcs);
> +struct phylink_pcs *_pcs_get_by_fwnode(const struct fwnode_handle *fwnode,
> +                                      const char *id, bool optional);
> +struct phylink_pcs *pcs_get_by_provider(const struct device *dev);
> +void pcs_put(struct phylink_pcs *pcs);
> +
> +static inline struct phylink_pcs
> +*pcs_get_by_fwnode(const struct fwnode_handle *fwnode,
> +                  const char *id)
> +{
> +       return _pcs_get_by_fwnode(fwnode, id, false);
> +}
> +
> +static inline struct phylink_pcs
> +*pcs_get_by_fwnode_optional(const struct fwnode_handle *fwnode, const char *id)
> +{
> +       return _pcs_get_by_fwnode(fwnode, id, true);
> +}
> +
> +#endif /* PCS_H */
> diff --git a/include/linux/phylink.h b/include/linux/phylink.h
> index 6d06896fc20d..a713e70108a1 100644
> --- a/include/linux/phylink.h
> +++ b/include/linux/phylink.h
> @@ -396,19 +396,24 @@ struct phylink_pcs_ops;
>
>  /**
>   * struct phylink_pcs - PHYLINK PCS instance
> + * @dev: the device associated with this PCS
>   * @ops: a pointer to the &struct phylink_pcs_ops structure
> + * @list: internal list of PCS devices
>   * @poll: poll the PCS for link changes
>   *
>   * This structure is designed to be embedded within the PCS private data,
>   * and will be passed between phylink and the PCS.
>   */
>  struct phylink_pcs {
> +       struct device *dev;
>         const struct phylink_pcs_ops *ops;
> +       struct list_head list;
>         bool poll;
>  };
>
>  /**
>   * struct phylink_pcs_ops - MAC PCS operations structure.
> + * @owner: the module which implements this PCS.
>   * @pcs_validate: validate the link configuration.
>   * @pcs_get_state: read the current MAC PCS link state from the hardware.
>   * @pcs_config: configure the MAC PCS for the selected mode and state.
> @@ -417,6 +422,7 @@ struct phylink_pcs {
>   *               (where necessary).
>   */
>  struct phylink_pcs_ops {
> +       struct module *owner;
>         int (*pcs_validate)(struct phylink_pcs *pcs, unsigned long *supported,
>                             const struct phylink_link_state *state);
>         void (*pcs_get_state)(struct phylink_pcs *pcs,
> --
> 2.35.1.1320.gc452695387.dirty
>

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