Re: [PATCH net-next 1/3] net: phy: Support enabling clocks prior to bus probe

[Rob Herring <robh+dt@kernel.org>]

On Wed, Sep 2, 2020 at 10:39 PM Florian Fainelli <f.fainelli@gmail.com> wrote:
>
> Some Ethernet PHYs may require that their clock, which typically drives
> their logic to respond to reads on the MDIO bus be enabled before
> issusing a MDIO bus scan.
>
> We have a chicken and egg problem though which is that we cannot enable
> a given Ethernet PHY's device clock until we have a phy_device instance
> create and called the driver's probe function. This will not happen
> unless we are successful in probing the PHY device, which requires its
> clock(s) to be turned on.
>
> For DT based systems we can solve this by using of_clk_get() which
> operates on a device_node reference, and make sure that all clocks
> associaed with the node are enabled prior to doing any reads towards the
> device. In order to avoid drivers having to know the a priori reference
> count of the resources, we drop them back to 0 right before calling
> ->probe() which is then supposed to manage the resources normally.

What if a device requires clocks enabled in a certain order or timing?
It's not just clocks, you could have some GPIOs or a regulator that
need enabling first. It's device specific, so really needs a per
device solution. This is not just an issue with MDIO. I think we
really need some sort of pre-probe hook in the driver model in order
to do any non-discoverable init for discoverable buses. Or perhaps
forcing probe when there are devices defined in DT if they're not
discovered by normal means.

However, you're not trying to do this in DT (see mmc-pwrseq :( ) and
this can evolve within the kernel to a better solution.

>
> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> ---
>  drivers/net/phy/phy_device.c | 15 +++++-
>  drivers/of/of_mdio.c         | 95 ++++++++++++++++++++++++++++++++++++

BTW, I'd really like to move this to drivers/net/ as we've done with
all the other bus/subsystem DT code.

>  include/linux/of_mdio.h      | 16 ++++++
>  include/linux/phy.h          | 13 +++++
>  4 files changed, 138 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 57d44648c8dd..bf2824ba056e 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -23,6 +23,7 @@
>  #include <linux/mm.h>
>  #include <linux/module.h>
>  #include <linux/netdevice.h>
> +#include <linux/of_mdio.h>
>  #include <linux/phy.h>
>  #include <linux/phy_led_triggers.h>
>  #include <linux/property.h>
> @@ -2845,6 +2846,15 @@ static int phy_probe(struct device *dev)
>
>         mutex_lock(&phydev->lock);
>
> +       /* To allow PHY drivers to manage device resources such as
> +        * clocks, regulators or others, disable the resources that
> +        * were enabled during the bus->reset or the PHY registration
> +        * routine such that they work with a natural resource reference
> +        * count.
> +        */
> +       of_mdiobus_device_disable_resources(phydev->mdio.bus,
> +                                           phydev->mdio.addr);
> +
>         /* Deassert the reset signal */
>         phy_device_reset(phydev, 0);
>
> @@ -2914,8 +2924,11 @@ static int phy_probe(struct device *dev)
>
>  out:
>         /* Assert the reset signal */
> -       if (err)
> +       if (err) {
>                 phy_device_reset(phydev, 1);
> +               of_mdiobus_device_disable_resources(phydev->mdio.bus,
> +                                                   phydev->mdio.addr);
> +       }
>
>         mutex_unlock(&phydev->lock);
>
> diff --git a/drivers/of/of_mdio.c b/drivers/of/of_mdio.c
> index cb32d7ef4938..bbce4a70312c 100644
> --- a/drivers/of/of_mdio.c
> +++ b/drivers/of/of_mdio.c
> @@ -19,6 +19,7 @@
>  #include <linux/of_mdio.h>
>  #include <linux/of_net.h>
>  #include <linux/module.h>
> +#include <linux/clk.h>
>
>  #define DEFAULT_GPIO_RESET_DELAY       10      /* in microseconds */
>
> @@ -60,6 +61,92 @@ static struct mii_timestamper *of_find_mii_timestamper(struct device_node *node)
>         return register_mii_timestamper(arg.np, arg.args[0]);
>  }
>
> +int of_mdiobus_device_enable_resources(struct mii_bus *bus,
> +                                      struct device_node *child,
> +                                      u32 addr)
> +{
> +       struct mdio_device_resource *res = &bus->mdio_resources[addr];
> +       unsigned int i;
> +       int rc;
> +
> +       if (res->enabled_resources) {
> +               dev_dbg(&bus->dev,
> +                       "MDIO resources for %d already enabled\n", addr);
> +               return 0;
> +       }
> +
> +       rc = of_count_phandle_with_args(child, "clocks", "#clock-cells");
> +       if (rc < 0) {
> +               if (rc == -ENOENT)
> +                       rc = 0;
> +               else
> +                       return rc;
> +       }
> +
> +       res->num_clks = rc;
> +       if (rc == 0)
> +               return rc;
> +
> +       dev_dbg(&bus->dev, "Found %d clocks for child at %d\n", rc, addr);
> +
> +       res->clks = devm_kcalloc(&bus->dev, res->num_clks,
> +                                sizeof(struct clk *), GFP_KERNEL);
> +       if (!res->clks)
> +               return -ENOMEM;
> +
> +       for (i = 0; i < res->num_clks; i++) {
> +               res->clks[i] = of_clk_get(child, i);
> +               if (IS_ERR(res->clks[i])) {
> +                       if (PTR_ERR(res->clks[i]) == -ENOENT)
> +                               continue;
> +
> +                       return PTR_ERR(res->clks[i]);

If you return here, you are potentially leaving clocks enabled and
with a reference.

> +               }
> +
> +               rc = clk_prepare_enable(res->clks[i]);

Can't you use clk_bulk_prepare_enable?

Looks like there's no bulk version of of_clk_get though...

> +               if (rc) {
> +                       dev_err(&bus->dev,
> +                               "Failed to enabled clock for %d (rc: %d)\n",
> +                               addr, rc);
> +                       goto out_clk_disable;
> +               }
> +
> +               dev_dbg(&bus->dev,
> +                       "Enable clock %d for child at %d\n",
> +                       i, addr);
> +       }
> +
> +       res->enabled_resources = true;
> +
> +       return 0;
> +
> +out_clk_disable:
> +       while (i-- > 0) {
> +               clk_disable_unprepare(res->clks[i]);
> +               clk_put(res->clks[i]);
> +       }
> +       res->enabled_resources = false;
> +       return rc;
> +}
> +EXPORT_SYMBOL(of_mdiobus_device_enable_resources);
> +
> +void of_mdiobus_device_disable_resources(struct mii_bus *bus, u32 addr)
> +{
> +       struct mdio_device_resource *res = &bus->mdio_resources[addr];
> +       unsigned int i;
> +
> +       if (!res->enabled_resources || res->num_clks == 0)
> +               return;
> +
> +       for (i = 0; i < res->num_clks; i++) {
> +               clk_disable_unprepare(res->clks[i]);
> +               clk_put(res->clks[i]);
> +               dev_dbg(&bus->dev, "Disabled clk %d for %d\n", i, addr);
> +       }
> +       res->enabled_resources = false;
> +}
> +EXPORT_SYMBOL(of_mdiobus_device_disable_resources);
> +
>  int of_mdiobus_phy_device_register(struct mii_bus *mdio, struct phy_device *phy,
>                               struct device_node *child, u32 addr)
>  {
> @@ -117,6 +204,12 @@ static int of_mdiobus_register_phy(struct mii_bus *mdio,
>         if (IS_ERR(mii_ts))
>                 return PTR_ERR(mii_ts);
>
> +       rc = of_mdiobus_device_enable_resources(mdio, child, addr);
> +       if (rc) {
> +               dev_err(&mdio->dev, "enable resources: %d\n", rc);
> +               return rc;
> +       }
> +
>         is_c45 = of_device_is_compatible(child,
>                                          "ethernet-phy-ieee802.3-c45");
>
> @@ -125,6 +218,7 @@ static int of_mdiobus_register_phy(struct mii_bus *mdio,
>         else
>                 phy = get_phy_device(mdio, addr, is_c45);
>         if (IS_ERR(phy)) {
> +               of_mdiobus_device_disable_resources(mdio, addr);
>                 if (mii_ts)
>                         unregister_mii_timestamper(mii_ts);
>                 return PTR_ERR(phy);
> @@ -132,6 +226,7 @@ static int of_mdiobus_register_phy(struct mii_bus *mdio,
>
>         rc = of_mdiobus_phy_device_register(mdio, phy, child, addr);
>         if (rc) {
> +               of_mdiobus_device_disable_resources(mdio, addr);
>                 if (mii_ts)
>                         unregister_mii_timestamper(mii_ts);
>                 phy_device_free(phy);
> diff --git a/include/linux/of_mdio.h b/include/linux/of_mdio.h
> index 1efb88d9f892..f43f4bcb3f22 100644
> --- a/include/linux/of_mdio.h
> +++ b/include/linux/of_mdio.h
> @@ -58,6 +58,10 @@ static inline int of_mdio_parse_addr(struct device *dev,
>         return addr;
>  }
>
> +int of_mdiobus_device_enable_resources(struct mii_bus *mdio,
> +                                      struct device_node *child, u32 addr);
> +void of_mdiobus_device_disable_resources(struct mii_bus *mdio, u32 addr);
> +
>  #else /* CONFIG_OF_MDIO */
>  static inline bool of_mdiobus_child_is_phy(struct device_node *child)
>  {
> @@ -129,6 +133,18 @@ static inline int of_mdiobus_phy_device_register(struct mii_bus *mdio,
>  {
>         return -ENOSYS;
>  }
> +
> +static inline int of_mdiobus_device_enable_resources(struct mii_bus *mdio,
> +                                                    struct device_node *child,
> +                                                    u32 addr)
> +{
> +       return 0;
> +}
> +
> +static inline void of_mdiobus_device_disable_resources(struct mii_bus *mdio,
> +                                                      u32 addr)
> +{
> +}
>  #endif
>
>
> diff --git a/include/linux/phy.h b/include/linux/phy.h
> index 3a09d2bf69ea..a01953daea45 100644
> --- a/include/linux/phy.h
> +++ b/include/linux/phy.h
> @@ -247,6 +247,14 @@ struct phy_package_shared {
>  #define PHY_SHARED_F_INIT_DONE  0
>  #define PHY_SHARED_F_PROBE_DONE 1
>
> +struct clk;
> +
> +struct mdio_device_resource {
> +       bool enabled_resources;
> +       unsigned int num_clks;
> +       struct clk **clks;
> +};
> +
>  /*
>   * The Bus class for PHYs.  Devices which provide access to
>   * PHYs should register using this structure
> @@ -291,6 +299,11 @@ struct mii_bus {
>          */
>         int irq[PHY_MAX_ADDR];
>
> +       /* An array of MDIO device resources that must be enabled
> +        * during probe for identification to succeed.
> +        */
> +       struct mdio_device_resource mdio_resources[PHY_MAX_ADDR];
> +
>         /* GPIO reset pulse width in microseconds */
>         int reset_delay_us;
>         /* GPIO reset deassert delay in microseconds */
> --
> 2.25.1
>