linux-kernel - Re: [PATCH] net: stmmac: don't stop RXC during LPI

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Message-ID: <Ye19vpFWXR8wJQVH@xhacker>
Date:   Mon, 24 Jan 2022 00:09:34 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Andrew Lunn <andrew@...n.ch>,
        Joakim Zhang <qiangqing.zhang@....com>
Cc:     Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: stmmac: don't stop RXC during LPI

On Mon, Jan 24, 2022 at 12:08:22AM +0800, Jisheng Zhang wrote:
> On Sun, Jan 23, 2022 at 04:52:29PM +0100, Andrew Lunn wrote:
> > On Sun, Jan 23, 2022 at 10:12:45PM +0800, Jisheng Zhang wrote:
> > > I met can't receive rx pkt issue with below steps:
> > > 0.plug in ethernet cable then boot normal and get ip from dhcp server
> > > 1.quickly hotplug out then hotplug in the ethernet cable
> > > 2.trigger the dhcp client to renew lease
> > > 
> > > tcpdump shows that the request tx pkt is sent out successfully,
> > > but the mac can't receive the rx pkt.
> > > 
> > > The issue can easily be reproduced on platforms with PHY_POLL external
> > > phy. If we don't allow the phy to stop the RXC during LPI, the issue
> > > is gone. I think it's unsafe to stop the RXC during LPI because the mac
> > > needs RXC clock to support RX logic.
> > > 
> > > And the 2nd param clk_stop_enable of phy_init_eee() is a bool, so use
> > > false instead of 0.
> > > 
> > > Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
> > > ---
> > >  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > > index 6708ca2aa4f7..92a9b0b226b1 100644
> > > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > > @@ -1162,7 +1162,7 @@ static void stmmac_mac_link_up(struct phylink_config *config,
> > >  
> > >  	stmmac_mac_set(priv, priv->ioaddr, true);
> > >  	if (phy && priv->dma_cap.eee) {
> > > -		priv->eee_active = phy_init_eee(phy, 1) >= 0;
> > > +		priv->eee_active = phy_init_eee(phy, false) >= 0;
> > 
> > This has not caused issues in the past. So i'm wondering if this is
> > somehow specific to your system? Does everybody else use a PHY which
> > does not implement this bit? Does your synthesis of the stmmac have a
> > different clock tree?
> > 
> > By changing this value for every instance of the stmmac, you are
> > potentially causing a power regression for stmmac implementations
> > which don't need the clock. So we need a clear understanding, stopping
> > the clock is wrong in general and so the change is correct in
> 
> I think this is a common issue because the MAC needs phy's RXC for RX
> logic. But it's better to let other stmmac users verify. The issue
> can easily be reproduced on platforms with PHY_POLL external phy.
> Or other platforms use a dedicated clock rather than clock from phy
> for MAC's RX logic?
> 
> If the issue turns out specific to my system, then I will send out
> a new patch to adopt your suggestion.
>

+ Joakim

> Hi Joakim, IIRC, you have stmmac + external RTL8211F phy platform, but
> I'm not sure whether your platform have an irq for the phy. could you
> help me to check whether you can reproduce the issue on your platform?
> 
> > general. Or this is specific to your system, and you probably need to
> > add priv->dma_cap.keep_rx_clock_ticking, which you set in your glue
> > driver,and use here to decide what to pass to phy_init_eee().
> 
> Thanks a lot for the suggestion.