Re: [PATCH net-next v2 0/2] net: phy: improve PHY suspend/resume

[Heiner Kallweit <hkallweit1@gmail.com>]

Am 24.05.2018 um 00:04 schrieb Andrew Lunn:
> On Wed, May 23, 2018 at 10:15:29PM +0200, Heiner Kallweit wrote:
>> I have the issue that suspending the MAC-integrated PHY gives an
>> error during system suspend. The sequence is:
>>
>> 1. unconnected PHY/MAC are runtime-suspended already
>> 2. system suspend commences
>> 3. mdio_bus_phy_suspend is called
>> 4. suspend callback of the network driver is called (implicitly
>>    MAC/PHY are runtime-resumed before)
>> 5. suspend callback suspends MAC/PHY
>>
>> The problem occurs in step 3. phy_suspend() fails because the MDIO
>> bus isn't accessible due to the chip being runtime-suspended.
> 
> I think you are fixing the wrong problem. I've had the same with the
> FEC driver. I fixed it by making the MDIO operations runtime-suspend
> aware:
> 
I checked the fec driver and there it's reletively easy because
runtime suspend/resume is just about disabling/enabling one clock.

In case of r8169 runtime suspend/resume do much more and there would
be quite some potential deadlock issues to take care of.
To provide one example:
pm_runtime_get_sync() would be called with the mdio bus lock being
held (from mdio write op), runtime-resuming however includes PHY
writes what would result in a deadlock.

I think we need a better solution than spending the effort needed
to make the MDIO ops runtime-pm-aware. In general there seems to be
just one network driver using both phylib and runtime pm, so most
drivers aren't affected (yet).

I will spend few more thoughts on a solution ..

Regards, Heiner

> commit 8fff755e9f8d0f70a595e79f248695ce6aef5cc3
> Author: Andrew Lunn <andrew@lunn.ch>
> Date:   Sat Jul 25 22:38:02 2015 +0200
> 
>     net: fec: Ensure clocks are enabled while using mdio bus
>     
>     When a switch is attached to the mdio bus, the mdio bus can be used
>     while the interface is not open. If the IPG clock is not enabled, MDIO
>     reads/writes will simply time out.
>     
>     Add support for runtime PM to control this clock. Enable/disable this
>     clock using runtime PM, with open()/close() and mdio read()/write()
>     function triggering runtime PM operations. Since PM is optional, the
>     IPG clock is enabled at probe and is no longer modified by
>     fec_enet_clk_enable(), thus if PM is not enabled in the kernel, it is
>     guaranteed the clock is running when MDIO operations are performed.
> 
> Don't copy this patch 1:1. I introduced a few bugs which took a while
> to be shaken out :-(
> 
>    Andrew
>