Re: [PATCH] sh_eth: ensure pm_runtime cannot suspend the device during init

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Ben and Sergei,

On Wednesday 19 March 2014 00:17:43 Sergei Shtylyov wrote:
> On 03/17/2014 05:01 PM, Ben Dooks wrote:
> >>>>> I have yet to ascertain how this ends up happening with device probe,
> >>>>> it seems to be very dependant on the code.
> >>>> 
> >>>> Adding a WARN() in cpg_mstp_clock_endisable():
> [...]
> 
> >>> this explains it, the call to stats causes a get_sync/put_sync which
> >>> puts the device into a state where it /could/ be suspended and thus
> >>> does get suspended in this case from the pm code.
> >>> 
> >>> I'm not /sure/ why the pm_runtime code is not protecting against
> >>> running this when a device probe is in progress, but it seems the
> >>> best thing is to ensure that we always do a get/put sync in the
> >>> driver to ensure we have a reference during probe.
> >> 
> >> Wouldn't it be better to register the MDIO bus before registering the
> >> network device ? It looks like the current order is prone to race
> >> conditions.
> >
> > Not sure, requires input?
> 
> People say that the driver should be ready to receive the ndo_open() method
> call even before register_netdev() returns. I have prepared the patch to
> probe MDIO before calling register_netdev() now, need to sanity test it.

Thank you.

> >> Another potential issue, does the network layer guarantee that the device
> >> will always be opened by an .ndo_open() call before performing any MDIO
> >> operation ? sh_mmd_ctrl, sh_set_mdio and sh_get_mdio access sh-eth
> >> registers, could we be missing runtime PM calls in those call paths ?
> > 
> > I'm not sure if there is any guarantee, I don't think the PHY driver
> > does any sort of open on probe. I do have a patch to ensure that the
> > MDIO operations are wrapped with pm_runtime_{get,put}_sync() calls as
> > the probe of the PHY often fails without it.
> 
> Respin this patch please (addressing my comments), so that DaveM could take
> it.

Before wrapping MDIO operations in runtime PM calls, could we check whether 
that's really needed ? Moving PHY registration before network device 
registration will fix PHY probe problems, we might not need any other change.

-- 
Regards,

Laurent Pinchart