netdev - Re: [PATCH 2/4] ravb: Add optional PHY reset during system resume

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Date:   Thu, 28 Sep 2017 10:22:48 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Geert Uytterhoeven <geert+renesas@...der.be>,
        "David S . Miller" <davem@...emloft.net>,
        Simon Horman <horms@...ge.net.au>,
        Magnus Damm <magnus.damm@...il.com>
Cc:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Andrew Lunn <andrew@...n.ch>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>, netdev@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 2/4] ravb: Add optional PHY reset during system resume

On 09/28/2017 08:53 AM, Geert Uytterhoeven wrote:
> If the optional "reset-gpios" property is specified in DT, the generic
> MDIO bus code takes care of resetting the PHY during device probe.
> However, the PHY may still have to be reset explicitly after system
> resume.
> 
> This allows to restore Ethernet operation after resume from s2ram on
> Salvator-XS, where the enable pin of the regulator providing PHY power
> is connected to PRESETn, and PSCI suspend powers down the SoC.
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
>  drivers/net/ethernet/renesas/ravb_main.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index fdf30bfa403bf416..96d1d48e302f8c9a 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> @@ -19,6 +19,7 @@
>  #include <linux/etherdevice.h>
>  #include <linux/ethtool.h>
>  #include <linux/if_vlan.h>
> +#include <linux/gpio/consumer.h>
>  #include <linux/kernel.h>
>  #include <linux/list.h>
>  #include <linux/module.h>
> @@ -2268,6 +2269,7 @@ static int __maybe_unused ravb_resume(struct device *dev)
>  {
>  	struct net_device *ndev = dev_get_drvdata(dev);
>  	struct ravb_private *priv = netdev_priv(ndev);
> +	struct mii_bus *bus = priv->mii_bus;
>  	int ret = 0;
>  
>  	if (priv->wol_enabled) {
> @@ -2302,6 +2304,13 @@ static int __maybe_unused ravb_resume(struct device *dev)
>  	 * reopen device if it was running before system suspended.
>  	 */
>  
> +	/* PHY reset */
> +	if (bus->reset_gpiod) {
> +		gpiod_set_value_cansleep(bus->reset_gpiod, 1);
> +		udelay(bus->reset_delay_us);
> +		gpiod_set_value_cansleep(bus->reset_gpiod, 0);
> +	}

This is a clever hack, but unfortunately this is also misusing the MDIO
bus reset line into a PHY reset line. As commented in patch 3, if this
reset line is tied to the PHY, then this should be a PHY property and
you cannot (ab)use the MDIO bus GPIO reset logic anymore...

Should not you also try to manage this reset line during ravb_open() to
achiever better power savings?
-- 
Florian