netdev - Re: Potential issue with f5e64032a799 "net: phy: fix resume handling"

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Message-ID: <1fa6517b-2a73-7c0c-48aa-afb17ff89440@gmail.com>
Date:   Sun, 4 Feb 2018 00:58:49 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Russell King <rmk+kernel@...linux.org.uk>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: Potential issue with f5e64032a799 "net: phy: fix resume handling"

Am 03.02.2018 um 21:17 schrieb Andrew Lunn:
> On Sat, Feb 03, 2018 at 05:41:54PM +0100, Heiner Kallweit wrote:
>> This commit forces callers of phy_resume() and phy_suspend() to hold
>> mutex phydev->lock. This was done for calls to phy_resume() and
>> phy_suspend() in phylib, however there are more callers in network
>> drivers. I'd assume that these other calls issue a warning now
>> because of the lock not being held.
>> So is there something I miss or would this have to be fixed?
> 
> Hi Heiner
> 
> This is a good point.
> 
> Yes, it looks like some fixes are needed. But what exactly?
> 
> The phy state machine will suspend and resume the phy is you call
> phy_stop() and phy_start() in the MAC suspend and resume functions.
> 
AFAICS phy_stop() doesn't suspend the PHY. It just sets the state
to PHY_HALTED and (at least if we're not in polling mode) doesn't
call phy_suspend(). Maybe a call to phy_trigger_machine() is
needed like in phy_start() ? Then the state machine would call
phy_suspend(), provided the link is still up.

However, if the link is down already (due to whatever calls
around phy_stop() in the driver) then phy_suspend() wouldn't be
called.

Heiner

> A few examples:
> 
> tc35815_suspend(), ravb_suspend() via ravb_close(), sh_eth_suspend()
> via sh_eth_close(), fec_suspend(), mpc52xx_fec_of_suspend() via
> mpc52xx_fec_close(), ucc_geth_suspend(), etc...
> 
> So i suspect those drivers which call phy_suspend()/phy_resume()
> should really be modified to call phy_stop()/phy_start().
> 
> hns_nic_config_phy_loopback() is just funky, and probably needs the
> help of the hns guys to fix.
> 
> dsa_slave_suspend() already does a phy_stop(), so the phy_suspend()
> can be removed.
> 
> The comments in lpc_eth_open() suggest the phy_resume() is needed, so
> locks should be added. socfpga_dwmac_resume() seems to be the same.
> 
>     Andrew
>