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

[Roger Quadros <rogerq@ti.com>]

On 19/04/17 16:38, Andrew Lunn wrote:
> On Wed, Apr 19, 2017 at 02:56:48PM +0300, Roger Quadros wrote:
>> Hi,
>>
>> On 19/04/17 14:39, Andrew Lunn wrote:
>>> 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@ti.com>
>>>> ---
>>>>  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.
>>
>> OK.
>>
>>>
>>>> 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.
>>
>> I was thinking from point of view that GPIO RESET code should work even without
>> device tree. Although I'm not sure if there would be any users or not.
> 
> Hi Roger
> 
> I don't see how this would work. What would devm_gpiod_get_index()
> return? Something from ACPI? But then there would be something

Yes or just lookup tables based on platform data.

> equivalent for getting the delay.

I'm not sure about delay part.

> 
> Lets keep it simple and OF only. If there is a real need for something
> in addition to OF, it can be added later.

OK. I'll revise the patch based on your comments.

cheers,
-roger