linux-kernel - Re: [PATCH] net/macb: add support for resetting PHY using GPIO

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Message-ID: <20151211102130.GA11966@pengutronix.de>
Date:	Fri, 11 Dec 2015 11:21:30 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Gregory CLEMENT <gregory.clement@...e-electrons.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Subject: Re: [PATCH] net/macb: add support for resetting PHY using GPIO

On Fri, Dec 11, 2015 at 10:40:22AM +0100, Gregory CLEMENT wrote:
> Hi Sascha,
>  
>  On ven., déc. 11 2015, Sascha Hauer <s.hauer@...gutronix.de> wrote:
> 
> > On Thu, Dec 10, 2015 at 04:08:08PM +0100, Gregory CLEMENT wrote:
> >> Hi Sascha,
> >>  
> >>  On jeu., déc. 10 2015, Sascha Hauer <s.hauer@...gutronix.de> wrote:
> >> 
> >> > Hi Gregory,
> >> >
> >> > On Wed, Dec 09, 2015 at 06:49:43PM +0100, Gregory CLEMENT wrote:
> >> >> With device tree it is no more possible to reset the PHY at board
> >> >> level. Furthermore, doing in the driver allow to power down the PHY when
> >> >> the network interface is no more used.
> >> >> 
> >> >> The patch introduces a new optional property "phy-reset-gpio" inspired
> >> >> from the one use for the FEC.
> >> >
> >> > I don't think it's a good idea to further extend the usage of this
> >> > binding. The driver should use the phy-handle property and
> >> > of_phy_connect() which gives you a proper device node for the phy. Then
> >> > the phy device node should get the reset gpio. I know it's more work,
> >> 
> >> So you suggest to pass from this binding:
> >> macb1: ethernet@...28000 {
> >> 	phy-mode = "rmii";
> >> 	status = "okay";
> >> 	#address-cells = <1>;
> >> 	#size-cells = <0>;
> >> 	status = "okay";
> >> 	phy-reset-gpio = <&pioE 6 GPIO_ACTIVE_HIGH>;
> >> 
> >> 	ethernet-phy@1 {
> >> 		reg = <0x1>;
> >> 		interrupt-parent = <&pioB>;
> >> 		interrupts = <31 IRQ_TYPE_EDGE_FALLING>;
> >> 
> >> 	};
> >> };
> >> 
> >> to this binding
> >> macb1: ethernet@...28000 {
> >> 	phy-mode = "rmii";
> >> 	status = "okay";
> >> 	#address-cells = <1>;
> >> 	#size-cells = <0>;
> >> 	status = "okay";
> >> 
> >> 	ethernet-phy@1 {
> >> 		reg = <0x1>;
> >> 		interrupt-parent = <&pioB>;
> >> 		interrupts = <31 IRQ_TYPE_EDGE_FALLING>;
> >>                 phy-reset-gpio = <&pioE 6 GPIO_ACTIVE_HIGH>;
> >> 	};
> >> };
> >
> > s/phy-reset-gpio/reset-gpios/, but yes.
> 
> So I took this way. But I had several issues. The first one was that to
> be able to create a phy device it must first be detected by
> get_phy_device from of_mdiobus_register_phy.  But in order to be
> detected it must answer during the scan of the mii bus. That means we
> can't bind the gpio to the device in order to use it because when we
> need to manage the reset gpio the device is not yet created.
> 
> So I see 2 options:
> 
> - leaving the phy-reset-gpios property in the ethernet node. Thanks to
>   this we can use the gpiod functions, and it is still possible to use
>   manage the power management.
> 
> - using a reset-gpios property inside the phy node. But then the only
>   solution to get a reference on it, will be to use
>   of_get_named_gpio. All the gpiod functions need a reference to the
>   device that we won't have at this point. Also we will only be able to
>   power up the reset, but we won't have any reference to it latter.

Have you seen fwnode_get_named_gpiod()? This seems to be the right
function for the job.

I think we should get the binding right. The code can be changed easier
than the binding later.

Sascha

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