Messages in this thread Patch in this message | | | From | Yan Markman <> | Subject | RE: [EXT] Re: [PATCH net] net: phylink: fix link state on phy-connect | Date | Sat, 2 Dec 2017 11:08:45 +0000 |
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Hi Russel The Grygorii has raised one Additional point (about netif_carrier_off) I just didn't want to start before finishing the previous one. On ifconfig-down the mac_config() called but with LINK=0. The config has no any knowledge what is intention -- up or down and should be done under disabled ingress/egress, and so the mac_config one of its action is netif_carrier_off.
After calling mac_config() the phylink checks if (!link && !netif_carrier_ok()) and decides to abort further down since all-done...
REMOVE netif_carrier_off looks like correct BUT has cases where de driver stops to works properly (sorry, I can't remember now what exactly). So finally I have placed there the CONDITIONAL carrier-off depending upon link:
static void mvpp2_mac_config(){ if (state->link) --- occasionally is TRUE on UP but FALSE on down netif_carrier_off(port->dev);//YANM
BTW: It's seems your below patch should be present anyway. +++ b/drivers/net/phy/phylink.c @@ -798,6 +798,7 @@ void phylink_disconnect_phy(struct phylink *pl) + pl->phy_state.link = false;
Thank you Best regards Yan Markman
-----Original Message----- From: Russell King - ARM Linux [mailto:linux@armlinux.org.uk] Sent: Friday, December 01, 2017 7:48 PM To: Florian Fainelli <f.fainelli@gmail.com> Cc: Grygorii Strashko <grygorii.strashko@ti.com>; Yan Markman <ymarkman@marvell.com>; Antoine Tenart <antoine.tenart@free-electrons.com>; andrew@lunn.ch; davem@davemloft.net; gregory.clement@free-electrons.com; thomas.petazzoni@free-electrons.com; miquel.raynal@free-electrons.com; Nadav Haklai <nadavh@marvell.com>; mw@semihalf.com; Stefan Chulski <stefanc@marvell.com>; netdev@vger.kernel.org; linux-kernel@vger.kernel.org Subject: Re: [EXT] Re: [PATCH net] net: phylink: fix link state on phy-connect
On Fri, Dec 01, 2017 at 09:36:42AM -0800, Florian Fainelli wrote: > On 12/01/2017 09:24 AM, Russell King - ARM Linux wrote: > > On Fri, Dec 01, 2017 at 11:07:22AM -0600, Grygorii Strashko wrote: > >> Hi Russell, > >> > >> On 11/30/2017 07:28 AM, Russell King - ARM Linux wrote: > >>> On Thu, Nov 30, 2017 at 10:10:18AM +0000, Russell King - ARM Linux wrote: > >>>> On Thu, Nov 30, 2017 at 08:51:21AM +0000, Yan Markman wrote: > >>>>> The phylink_stop is called before phylink_disconnect_phy You > >>>>> could see in mvpp2.c: > >>>>> > >>>>> mvpp2_stop_dev() { > >>>>> phylink_stop(port->phylink); > >>>>> } > >>>>> > >>>>> mvpp2_stop() { > >>>>> mvpp2_stop_dev(port); > >>>>> phylink_disconnect_phy(port->phylink); > >>>>> } > >>>>> > >>>>> .ndo_stop = mvpp2_stop, > >>>> > >>>> Sorry, I don't have this in mvpp2.c, so I have no visibility of > >>>> what you're working with. > >>>> > >>>> What you have above looks correct, and I see no reason why the > >>>> p21 patch would not have resolved your issue. The p21 patch > >>>> ensures that phylink_resolve() gets called and completes before > >>>> phylink_stop() returns. In that case, phylink_resolve() will > >>>> call the mac_link_down() method if the link is not already down. > >>>> It will also print the "Link is Down" message. > >>>> > >>>> Florian has already tested this patch after encountering a > >>>> similar issue, and has reported that it solves the problem for > >>>> him. I've also tested it with mvneta, and the original mvpp2x driver on Macchiatobin. > >>>> > >>>> Maybe there's something different about mvpp2, but as I have no > >>>> visibility of that driver and the modifications therein, I can't > >>>> comment further other than stating that it works for three > >>>> different implementations. > >>>> > >>>> Maybe you could try and work out what's going on with the p21 > >>>> patch in your case? > >>> > >>> I think I now realise what's probably going on. > >>> > >>> If you call netif_carrier_off() before phylink_stop(), then > >>> phylink will believe that the link is already down, and so it > >>> won't bother calling > >>> mac_link_down() - it will believe that the link is already down. > >>> > >>> I'll update the documentation for phylink_stop() to spell out this > >>> aspect. > >>> > >> > >> There are pretty high number of net drivers which do call > >> netif_carrier_off(dev); > >> before > >> phy_stop(dev->phydev); > >> in .ndo_stop() callback. > >> > >> As per you comment this seems to be incorrect, so should such calls > >> be removed? > > > > Well, I think the question that needs to be asked is this: > > > > Is calling netif_carrier_off() before phy_stop() safe? > > > > Well, reading the phylib code, this is the answer I've come to: > > > > Between phy_start() and phy_stop(), phylib is free to manage the > > carrier state itself through the phylib state machine. > > > > This means if you call netif_carrier_off() prior to phy_stop(), > > there is nothing preventing the phylib state machine from running, > > and a co-incident poll of the PHY could notice that the link has > > come up, and re-enable the carrier while your ndo_stop() method > > is still running. > > > > So, my conclusion is that this practice is provably racy, though > > it's probably not that easy to trigger the race (which is probably > > why no one has reported the problem.) > > > > Given that it's racy, it's not something that I think phylink should > > care about, and should "softly" discourage it. So, I'm happy with > > what phylink is doing here, and I suggest fixing the drivers for > > this race. > > > > In any case, it should result in less code in the drivers - since > > the work you need to do when the link goes down is a subset of the > > work you need to do when the network interface is taken down. > > > > While I agree with all of what written before, in practice, calling > netif_carrier_off() when using PHYLIB can cause inconsistent carrier > states at most, but it would not be messing the state machine itself > because PHYLIB does not make uses of netif_carrier_ok() to make any > decisions as whether the link has dropped or not, it bases its > information solely on phydev->link.
Indeed, but the point I'm making is that this sequence is very possible with drivers that mess about by fiddling with stuff before they call phy_stop():
CPU0 CPU1 netif_carrier_off() mvpp2_egress_disable() phy_state_machine() (phydev->state = PHY_AN) phy_link_up() phy_link_change() netif_carrier_on() mvpp2_link_event() mvpp2_egress_enable() mvpp2_ingress_enable() mvpp2_port_disable() phy_stop(ndev->phydev) At this point, egress has not been disabled as mvpp2_stop_dev() wants, because the phylib state machine got in before it was stopped, called the adjust link function which then had the effect of re-enabling the egress.
If that doesn't matter, then what's the point of the mvpp2_egress_disable() call in the mvpp2_stop_dev() path... either it matters and the mvpp2_stop_dev() sequence is broken, or it doesn't matter and some the work that mvpp2_stop_dev() is doing is unnecessary.
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