Date:   Tue, 6 Apr 2021 01:39:00 +0000
From:   Joakim Zhang <qiangqing.zhang@....com>
To:     Heiner Kallweit <hkallweit1@...il.com>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        "christian.melki@...ata.com" <christian.melki@...ata.com>
Subject: RE: [PATCH] net: phy: fix PHY possibly unwork after MDIO bus resume
 back


Hi Heiner,

> -----Original Message-----
> From: Heiner Kallweit <hkallweit1@...il.com>
> Sent: 2021年4月5日 6:49
> To: Joakim Zhang <qiangqing.zhang@....com>; andrew@...n.ch;
> linux@...linux.org.uk; davem@...emloft.net; kuba@...nel.org
> Cc: netdev@...r.kernel.org; linux-kernel@...r.kernel.org; dl-linux-imx
> <linux-imx@....com>; christian.melki@...ata.com
> Subject: Re: [PATCH] net: phy: fix PHY possibly unwork after MDIO bus resume
> back
> 
> On 04.04.2021 16:09, Heiner Kallweit wrote:
> > On 04.04.2021 12:07, Joakim Zhang wrote:
> >> commit 4c0d2e96ba055 ("net: phy: consider that suspend2ram may cut
> >> off PHY power") invokes phy_init_hw() when MDIO bus resume, it will
> >> soft reset PHY if PHY driver implements soft_reset callback.
> >> commit 764d31cacfe4 ("net: phy: micrel: set soft_reset callback to
> >> genphy_soft_reset for KSZ8081") adds soft_reset for KSZ8081. After
> >> these two patches, I found i.MX6UL 14x14 EVK which connected to
> >> KSZ8081RNB doesn't work any more when system resume back, MAC driver
> is fec_main.c.
> >>
> >> It's obvious that initializing PHY hardware when MDIO bus resume back
> >> would introduce some regression when PHY implements soft_reset. When
> >> I
> >
> > Why is this obvious? Please elaborate on why a soft reset should break
> > something.
> >
> >> am debugging, I found PHY works fine if MAC doesn't support
> >> suspend/resume or phy_stop()/phy_start() doesn't been called during
> >> suspend/resume. This let me realize, PHY state machine
> >> phy_state_machine() could do something breaks the PHY.
> >>
> >> As we known, MAC resume first and then MDIO bus resume when system
> >> resume back from suspend. When MAC resume, usually it will invoke
> >> phy_start() where to change PHY state to PHY_UP, then trigger the
> >> stat> machine to run now. In phy_state_machine(), it will
> >> start/config auto-nego, then change PHY state to PHY_NOLINK, what to
> >> next is periodically check PHY link status. When MDIO bus resume, it
> >> will initialize PHY hardware, including soft_reset, what would
> >> soft_reset affect seems various from different PHYs. For KSZ8081RNB,
> >> when it in PHY_NOLINK state and then perform a soft reset, it will never
> complete auto-nego.
> >
> > Why? That would need to be checked in detail. Maybe chip errata
> > documentation provides a hint.
> >
> 
> The KSZ8081 spec says the following about bit BMCR_PDOWN:
> 
> If software reset (Register 0.15) is
> used to exit power-down mode
> (Register 0.11 = 1), two software
> reset writes (Register 0.15 = 1) are
> required. The first write clears
> power-down mode; the second
> write resets the chip and re-latches
> the pin strapping pin values.
> 
> Maybe this causes the issue you see and genphy_soft_reset() isn't appropriate
> for this PHY. Please re-test with the KSZ8081 soft reset following the spec
> comment.

Yes, I also noticed this note in spec, and tried to soft reset twice from PHY driver, but still can't work.

What is strange is that, ifup/ifdown can work fine, which is almost the same route with suspend/resume,
except suspend/resume has state machine running. 

> 
> >>
> >> This patch changes PHY state to PHY_UP when MDIO bus resume back, it
> >> should be reasonable after PHY hardware re-initialized. Also give
> >> state machine a chance to start/config auto-nego again.
> >>
> >
> > If the MAC driver calls phy_stop() on suspend, then phydev->suspended
> > is true and mdio_bus_phy_may_suspend() returns false. As a consequence
> > phydev->suspended_by_mdio_bus is false and mdio_bus_phy_resume()
> > skips the PHY hw initialization.
> > Please also note that mdio_bus_phy_suspend() calls phy_stop_machine()
> > that sets the state to PHY_UP.
> >
> 
> Forgot that MDIO bus suspend is done before MAC driver suspend.
> Therefore disregard this part for now.

OK.

Best Regards,
Joakim Zhang
> > Having said that the current argumentation isn't convincing. I'm not
> > aware of such issues on other systems, therefore it's likely that
> > something is system-dependent.
> >
> > Please check the exact call sequence on your system, maybe it provides
> > a hint.
> >
> >> Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
> >> ---
> >>  drivers/net/phy/phy_device.c | 7 +++++++
> >>  1 file changed, 7 insertions(+)
> >>
> >> diff --git a/drivers/net/phy/phy_device.c
> >> b/drivers/net/phy/phy_device.c index cc38e326405a..312a6f662481
> >> 100644
> >> --- a/drivers/net/phy/phy_device.c
> >> +++ b/drivers/net/phy/phy_device.c
> >> @@ -306,6 +306,13 @@ static __maybe_unused int
> mdio_bus_phy_resume(struct device *dev)
> >>  	ret = phy_resume(phydev);
> >>  	if (ret < 0)
> >>  		return ret;
> >> +
> >> +	/* PHY state could be changed to PHY_NOLINK from MAC controller
> resume
> >> +	 * rounte with phy_start(), here change to PHY_UP after re-initializing
> >> +	 * PHY hardware, let PHY state machine to start/config auto-nego again.
> >> +	 */
> >> +	phydev->state = PHY_UP;
> >> +
> >>  no_resume:
> >>  	if (phydev->attached_dev && phydev->adjust_link)
> >>  		phy_start_machine(phydev);
> >>
> >

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