linux-kernel - Re: [PATCH] net: phy: micrel: reconfigure the phy on resume

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Date:   Wed, 13 Jan 2021 09:29:32 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <hkallweit1@...il.com>, <andrew@...n.ch>, <linux@...linux.org.uk>,
        <davem@...emloft.net>, <kuba@...nel.org>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: phy: micrel: reconfigure the phy on resume

Hi Heiner,

On 08.01.2021 18:31, Heiner Kallweit wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On 08.01.2021 16:45, Claudiu Beznea wrote:
>> KSZ9131 is used in setups with SAMA7G5. SAMA7G5 supports a special
>> power saving mode (backup mode) that cuts the power for almost all
>> parts of the SoC. The rail powering the ethernet PHY is also cut off.
>> When resuming, in case the PHY has been configured on probe with
>> slew rate or DLL settings these needs to be restored thus call
>> driver's config_init() on resume.
>>
> When would the SoC enter this backup mode?

It could enter in this mode based on request for standby or suspend-to-mem:
echo mem > /sys/power/state
echo standby > /sys/power/state

What I didn't mentioned previously is that the RAM remains in self-refresh
while the rest of the SoC is powered down.

> And would it suspend the
> MDIO bus before cutting power to the PHY?

SAMA7G5 embeds Cadence macb driver which has a integrated MDIO bus. Inside
macb driver the bus is registered with of_mdiobus_register() or
mdiobus_register() based on the PHY devices present in DT or not. On macb
suspend()/resume() functions there are calls to
phylink_stop()/phylink_start() before cutting/after enabling the power to
the PHY.

> I'm asking because in mdio_bus_phy_restore() we call phy_init_hw()
> already (that calls the driver's config_init).

As far as I can see from documentation the .restore API of dev_pm_ops is
hibernation specific (please correct me if I'm wrong). On transitions to
backup mode the suspend()/resume() PM APIs are called on the drivers.

Thank you,
Claudiu Beznea

> 
>> Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
>> ---
>>  drivers/net/phy/micrel.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/phy/micrel.c b/drivers/net/phy/micrel.c
>> index 3fe552675dd2..52d3a0480158 100644
>> --- a/drivers/net/phy/micrel.c
>> +++ b/drivers/net/phy/micrel.c
>> @@ -1077,7 +1077,7 @@ static int kszphy_resume(struct phy_device *phydev)
>>        */
>>       usleep_range(1000, 2000);
>>
>> -     ret = kszphy_config_reset(phydev);
>> +     ret = phydev->drv->config_init(phydev);
>>       if (ret)
>>               return ret;
>>
>>
>