netdev - Re: [RFC PATCH net-next 1/3] net: phy: don't bind genphy in phy_attach_direct if the specific driver defers probe

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Date:   Fri, 3 Sep 2021 02:26:07 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     "Russell King (Oracle)" <linux@...linux.org.uk>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        netdev@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Vivien Didelot <vivien.didelot@...il.com>,
        linux-kernel@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Alvin Šipraga <alsi@...g-olufsen.dk>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        kernel-team <kernel-team@...roid.com>,
        Len Brown <lenb@...nel.org>
Subject: Re: [RFC PATCH net-next 1/3] net: phy: don't bind genphy in
 phy_attach_direct if the specific driver defers probe

On Fri, Sep 03, 2021 at 01:02:06AM +0200, Andrew Lunn wrote:
> We should try to keep phylink_create and phylink_destroy symmetrical:
> 
> /**
>  * phylink_create() - create a phylink instance
>  * @config: a pointer to the target &struct phylink_config
>  * @fwnode: a pointer to a &struct fwnode_handle describing the network
>  *      interface
>  * @iface: the desired link mode defined by &typedef phy_interface_t
>  * @mac_ops: a pointer to a &struct phylink_mac_ops for the MAC.
>  *
>  * Create a new phylink instance, and parse the link parameters found in @np.
>  * This will parse in-band modes, fixed-link or SFP configuration.
>  *
>  * Note: the rtnl lock must not be held when calling this function.
> 
> Having different locking requirements will catch people out.
> 
> Interestingly, there is no ASSERT_NO_RTNL(). Maybe we should add such
> a macro.

In this case, the easiest might be to just take a different mutex in
dpaa2 which serializes all places that access the priv->mac references.
I don't know exactly why the SFP bus needs the rtnl_mutex, I've removed
those locks and will see what fails tomorrow, but I don't think dpaa2
has a good enough justification to take the rtnl_mutex just so that it
can connect and disconnect to the MAC freely at runtime.