netdev - Re: [PATCH] phy: add support for a reset-gpio specification

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Message-ID: <658c33a1-3304-8b0c-abfd-9e2a8b556d29@cogentembedded.com>
Date:	Fri, 13 May 2016 22:10:40 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc:	netdev@...r.kernel.org, devicetree@...r.kernel.org,
	Florian Fainelli <f.fainelli@...il.com>, kernel@...gutronix.de,
	"Andrew F . Davis" <afd@...com>, Nishanth Menon <nm@...com>
Subject: Re: [PATCH] phy: add support for a reset-gpio specification

Hello.

On 05/13/2016 09:26 AM, Uwe Kleine-König wrote:

>>> The framework only asserts (for now) that the reset gpio is not active.
>>>
>>> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
>>> ---
>>> Documentation/devicetree/bindings/net/phy.txt | 3 +++
>>> drivers/net/phy/phy_device.c                  | 8 ++++++++
>>> 2 files changed, 11 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/net/phy.txt b/Documentation/devicetree/bindings/net/phy.txt
>>> index bc1c3c8bf8fa..c00a9a894547 100644
>>> --- a/Documentation/devicetree/bindings/net/phy.txt
>>> +++ b/Documentation/devicetree/bindings/net/phy.txt
>>> @@ -35,6 +35,8 @@ Optional Properties:
>>> - broken-turn-around: If set, indicates the PHY device does not correctly
>>>   release the turn around line low at the end of a MDIO transaction.
>>>
>>> +- reset-gpios: Reference to a GPIO used to reset the phy.
>>> +
>>> Example:
>>>
>>> ethernet-phy@0 {
>>> @@ -42,4 +44,5 @@ ethernet-phy@0 {
>>> 	interrupt-parent = <40000>;
>>> 	interrupts = <35 1>;
>>> 	reg = <0>;
>>> +	reset-gpios = <&gpio1 17 GPIO_ACTIVE_LOW>;
>>>  };
>>
>>    OK, the example has PHY ID specified in the "compatible" prop. It's a
>> vital detail, you should mention it somewhere...
>
> Something like that in the commit log:
>
> 	Note that reset is only deasserted when the PHY ID is already
> 	determined. If your phy doesn't support reading the PHY ID while
> 	reset is asserted it's recommended to specify it in the
> 	compatible string. Otherwise the device might fail to probe.

    Yes, that should do.

>>> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
>>> index e551f3a89cfd..7d666ab47271 100644
>>> --- a/drivers/net/phy/phy_device.c
>>> +++ b/drivers/net/phy/phy_device.c
>> [...]
>>> @@ -1569,9 +1570,16 @@ static int phy_probe(struct device *dev)
>>> 	struct device_driver *drv = phydev->mdio.dev.driver;
>>> 	struct phy_driver *phydrv = to_phy_driver(drv);
>>> 	int err = 0;
>>> +	struct gpio_descs *reset_gpios;
>>>
>>> 	phydev->drv = phydrv;
>>>
>>> +	/* take phy out of reset */
>>> +	reset_gpios = devm_gpiod_get_array_optional(dev, "reset",
>>> +						    GPIOD_OUT_LOW);
>>> +	if (IS_ERR(reset_gpios))
>>> +		return PTR_ERR(reset_gpios);
>>> +
>>
>>    It would have been logical to assert back the reset GPIO in phy_remove(),

> Not necessarily. If you want to save some energy it might make sense. If

    Yes, we'd like to do that. Florian (the phylib maintainer) even wanted 
asserting reset during the PM suspended state.

> you only focus on making the device work, ensuring that reset is not
> applied is enough.

>> no? Also, you'd need to store the GPIO permanently somewhere...
>
> I need to store it, iff I want to do something with the reset line
> later. Currently that's not the case.

    Oops, I seem to somewhat muddled up here. Of course, you need to store it 
if you intend to de-assert it later.

> Best regards
> Uwe

MBR, Sergei