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

[<Claudiu.Beznea@microchip.com>]

On 13.01.2021 13:09, Heiner Kallweit wrote:
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> 
> On 13.01.2021 10:29, Claudiu.Beznea@microchip.com wrote:
>> 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.
>>
> 
> This leaves the question which driver sets backup mode in the SoC.

From Linux point of view the backup mode is a standard suspend-to-mem PM
mode. The only difference is in SoC specific PM code
(arch/arm/mach-at91/pm_suspend.S) where the SoC shutdown command is
executed at the end and the fact that we save the address in RAM of
cpu_resume() function in a powered memory. Then, the resume is done with
the help of bootloader (it configures necessary clocks) and jump the
execution to the previously saved address, resuming Linux.

> Whatever/whoever wakes the SoC later would have to take care that basically
> everything that was switched off is reconfigured (incl. calling phy_init_hw()).

For this the bootloader should know the PHY settings passed via DT (skew
settings or DLL settings). The bootloader runs from a little SRAM which, at
the moment doesn't know to parse DT bindings and the DT parsing lib might
be big enough that the final bootloader size will cross the SRAM size.

> So it' more or less the same as waking up from hibernation. Therefore I think
> the .restore of all subsystems would have to be executed, incl. .restore of
> the MDIO bus.

I see your point. I think it has been implemented like a standard
suspend-to-mem PM mode because the RAM remains in self-refresh whereas in
hibernation it is shut of (as far as I know).

> Having said that I don't think that change belongs into the
> PHY driver.
> Just imagine tomorrow another PHY type is used in a SAMA7G5 setup.
> Then you would have to do same change in another PHY driver.

I understand this. At the moment the PM code for drivers in SAMA7G5 are
saving/restoring in/from RAM the registers content in suspend/resume()
functions of each drivers and I think it has been chosen like this as the
RAM remains in self-refresh. Mapping this mode to hibernation will involve
saving the content of RAM to a non-volatile support which is not wanted as
this increases the suspend/resume time and it wasn't intended.

> 
> 
>>> 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@microchip.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;
>>>>
>>>>
>