Re: [PATCH] mdio_bus: Issue GPIO RESET to PHYs.

[Andrew Lunn]

On Wed, Apr 19, 2017 at 12:24:26PM +0300, Roger Quadros wrote:
> Some boards [1] leave the PHYs at an invalid state
> during system power-up or reset thus causing unreliability
> issues with the PHY which manifests as PHY not being detected
> or link not functional. To fix this, these PHYs need to be RESET
> via a GPIO connected to the PHY's RESET pin.
> 
> Some boards have a single GPIO controlling the PHY RESET pin of all
> PHYs on the bus whereas some others have separate GPIOs controlling
> individual PHY RESETs.
> 
> In both cases, the RESET de-assertion cannot be done in the PHY driver
> as the PHY will not probe till its reset is de-asserted.
> So do the RESET de-assertion in the MDIO bus driver.
> 
> [1] - am572x-idk, am571x-idk, a437x-idk
> 
> Signed-off-by: Roger Quadros <rogerq@xxxxxx>
> ---
>  drivers/net/phy/mdio_bus.c | 26 ++++++++++++++++++++++++++
>  drivers/of/of_mdio.c       |  4 ++++
>  include/linux/phy.h        |  5 +++++
>  3 files changed, 35 insertions(+)

Hi Roger

Thanks for making this generic.

Please add device tree binding documentation. I think that actually
means you have to document MDIO in general, since there currently is
not a binding document.

> diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
> index fa7d51f..25fda2b 100644
> --- a/drivers/net/phy/mdio_bus.c
> +++ b/drivers/net/phy/mdio_bus.c
> @@ -22,8 +22,11 @@
>  #include <linux/init.h>
>  #include <linux/delay.h>
>  #include <linux/device.h>
> +#include <linux/gpio.h>
> +#include <linux/gpio/consumer.h>
>  #include <linux/of_device.h>
>  #include <linux/of_mdio.h>
> +#include <linux/of_gpio.h>
>  #include <linux/netdevice.h>
>  #include <linux/etherdevice.h>
>  #include <linux/skbuff.h>
> @@ -43,6 +46,8 @@
>  
>  #include "mdio-boardinfo.h"
>  
> +#define DEFAULT_GPIO_RESET_DELAY	10	/* in microseconds */
> +
>  int mdiobus_register_device(struct mdio_device *mdiodev)
>  {
>  	if (mdiodev->bus->mdio_map[mdiodev->addr])
> @@ -307,6 +312,7 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner)
>  {
>  	struct mdio_device *mdiodev;
>  	int i, err;
> +	struct gpio_desc *gpiod;
>  
>  	if (NULL == bus || NULL == bus->name ||
>  	    NULL == bus->read || NULL == bus->write)
> @@ -333,6 +339,26 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner)
>  	if (bus->reset)
>  		bus->reset(bus);
>  
> +	/* de-assert bus level PHY GPIO resets */
> +	for (i = 0; i < bus->num_reset_gpios; i++) {
> +		gpiod = devm_gpiod_get_index(&bus->dev, "reset", i,
> +					     GPIOD_OUT_LOW);
> +		if (IS_ERR(gpiod)) {
> +			err = PTR_ERR(gpiod);
> +			if (err != -ENOENT) {
> +				pr_err("mii_bus %s couldn't get reset GPIO\n",
> +				       bus->id);
> +				return err;
> +			}
> +		} else {
> +			gpiod_set_value_cansleep(gpiod, 1);


> +			if (!bus->reset_delay_us)
> +				bus->reset_delay_us = DEFAULT_GPIO_RESET_DELAY;

Maybe do this once, where you read the device tree property.


> +			udelay(bus->reset_delay_us);
> +			gpiod_set_value_cansleep(gpiod, 0);
> +		}
> +	}
> +
>  	for (i = 0; i < PHY_MAX_ADDR; i++) {
>  		if ((bus->phy_mask & (1 << i)) == 0) {
>  			struct phy_device *phydev;
> diff --git a/drivers/of/of_mdio.c b/drivers/of/of_mdio.c
> index 0b29798..83a62e4 100644
> --- a/drivers/of/of_mdio.c
> +++ b/drivers/of/of_mdio.c
> @@ -221,6 +221,10 @@ int of_mdiobus_register(struct mii_bus *mdio, struct device_node *np)
>  
>  	mdio->dev.of_node = np;
>  
> +	/* Get bus level PHY reset GPIO details */
> +	of_property_read_u32(np, "reset-delay-us", &mdio->reset_delay_us);

If the property does not exist, it is guaranteed mdio->reset_delay_us
is not changed. So you can set it to the default value before, then do
this call.

     Andrew