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Date: Thu, 30 Nov 2023 15:09:36 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Serge Semin <fancer.lancer@...il.com>
Cc: Jianheng Zhang <Jianheng.Zhang@...opsys.com>, Alexandre Torgue
 <alexandre.torgue@...s.st.com>, Jose Abreu <Jose.Abreu@...opsys.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,  Maxime Coquelin
 <mcoquelin.stm32@...il.com>, Simon Horman <horms@...nel.org>, Andrew
 Halaney <ahalaney@...hat.com>,  Bartosz Golaszewski
 <bartosz.golaszewski@...aro.org>, Shenwei Wang <shenwei.wang@....com>,
 Johannes Zink <j.zink@...gutronix.de>, "Russell King (Oracle"
 <rmk+kernel@...linux.org.uk>,  Jochen Henneberg
 <jh@...neberg-systemdesign.com>, Voon Weifeng <weifeng.voon@...el.com>,
 Mohammad Athari Bin Ismail <mohammad.athari.ismail@...el.com>, Ong Boon
 Leong <boon.leong.ong@...el.com>,  Tan Tee Min <tee.min.tan@...el.com>,
 "open list:STMMAC ETHERNET DRIVER" <netdev@...r.kernel.org>,  "moderated
 list:ARM/STM32 ARCHITECTURE" <linux-stm32@...md-mailman.stormreply.com>,
 "moderated list:ARM/STM32 ARCHITECTURE"
 <linux-arm-kernel@...ts.infradead.org>, open list
 <linux-kernel@...r.kernel.org>, James Li <James.Li1@...opsys.com>, Martin
 McKenny <Martin.McKenny@...opsys.com>
Subject: Re: [PATCH v3] net: stmmac: fix FPE events losing

On Thu, 2023-11-30 at 16:09 +0300, Serge Semin wrote:
> Hi Paolo
> 
> On Thu, Nov 30, 2023 at 10:55:34AM +0100, Paolo Abeni wrote:
> > On Tue, 2023-11-28 at 05:56 +0000, Jianheng Zhang wrote:
> > > The status bits of register MAC_FPE_CTRL_STS are clear on read. Using
> > > 32-bit read for MAC_FPE_CTRL_STS in dwmac5_fpe_configure() and
> > > dwmac5_fpe_send_mpacket() clear the status bits. Then the stmmac interrupt
> > > handler missing FPE event status and leads to FPE handshaking failure and
> > > retries.
> > > To avoid clear status bits of MAC_FPE_CTRL_STS in dwmac5_fpe_configure()
> > > and dwmac5_fpe_send_mpacket(), add fpe_csr to stmmac_fpe_cfg structure to
> > > cache the control bits of MAC_FPE_CTRL_STS and to avoid reading
> > > MAC_FPE_CTRL_STS in those methods.
> > > 
> > > Fixes: 5a5586112b92 ("net: stmmac: support FPE link partner hand-shaking procedure")
> > > Reviewed-by: Serge Semin <fancer.lancer@...il.com>
> > > Signed-off-by: Jianheng Zhang <jianheng@...opsys.com>
> > > ---
> > >  drivers/net/ethernet/stmicro/stmmac/dwmac5.c       | 45 +++++++++-------------
> > >  drivers/net/ethernet/stmicro/stmmac/dwmac5.h       |  4 +-
> > >  .../net/ethernet/stmicro/stmmac/dwxgmac2_core.c    |  3 +-
> > >  drivers/net/ethernet/stmicro/stmmac/hwif.h         |  4 +-
> > >  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c  |  8 +++-
> > >  drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c    |  1 +
> > >  include/linux/stmmac.h                             |  1 +
> > >  7 files changed, 36 insertions(+), 30 deletions(-)
> > > 
> > > diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac5.c b/drivers/net/ethernet/stmicro/stmmac/dwmac5.c
> > > index e95d35f..8fd1675 100644
> > > --- a/drivers/net/ethernet/stmicro/stmmac/dwmac5.c
> > > +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac5.c
> > > @@ -710,28 +710,22 @@ void dwmac5_est_irq_status(void __iomem *ioaddr, struct net_device *dev,
> > >  	}
> > >  }
> > >  
> > > -void dwmac5_fpe_configure(void __iomem *ioaddr, u32 num_txq, u32 num_rxq,
> > > +void dwmac5_fpe_configure(void __iomem *ioaddr, struct stmmac_fpe_cfg *cfg,
> > > +			  u32 num_txq, u32 num_rxq,
> > >  			  bool enable)
> > >  {
> > >  	u32 value;
> > >  
> > > -	if (!enable) {
> > > -		value = readl(ioaddr + MAC_FPE_CTRL_STS);
> > > -
> > > -		value &= ~EFPE;
> > > -
> > > -		writel(value, ioaddr + MAC_FPE_CTRL_STS);
> > > -		return;
> > > +	if (enable) {
> > > +		cfg->fpe_csr = EFPE;
> > > +		value = readl(ioaddr + GMAC_RXQ_CTRL1);
> > > +		value &= ~GMAC_RXQCTRL_FPRQ;
> > > +		value |= (num_rxq - 1) << GMAC_RXQCTRL_FPRQ_SHIFT;
> > > +		writel(value, ioaddr + GMAC_RXQ_CTRL1);
> > > +	} else {
> > > +		cfg->fpe_csr = 0;
> > >  	}
> > > -
> > > -	value = readl(ioaddr + GMAC_RXQ_CTRL1);
> > > -	value &= ~GMAC_RXQCTRL_FPRQ;
> > > -	value |= (num_rxq - 1) << GMAC_RXQCTRL_FPRQ_SHIFT;
> > > -	writel(value, ioaddr + GMAC_RXQ_CTRL1);
> > > -
> > > -	value = readl(ioaddr + MAC_FPE_CTRL_STS);
> > > -	value |= EFPE;
> > > -	writel(value, ioaddr + MAC_FPE_CTRL_STS);
> > > +	writel(cfg->fpe_csr, ioaddr + MAC_FPE_CTRL_STS);
> > >  }
> > >  
> > >  int dwmac5_fpe_irq_status(void __iomem *ioaddr, struct net_device *dev)
> > > @@ -741,6 +735,9 @@ int dwmac5_fpe_irq_status(void __iomem *ioaddr, struct net_device *dev)
> > >  
> > >  	status = FPE_EVENT_UNKNOWN;
> > >  
> > > +	/* Reads from the MAC_FPE_CTRL_STS register should only be performed
> > > +	 * here, since the status flags of MAC_FPE_CTRL_STS are "clear on read"
> > > +	 */
> > >  	value = readl(ioaddr + MAC_FPE_CTRL_STS);
> > >  
> > >  	if (value & TRSP) {
> > > @@ -766,19 +763,15 @@ int dwmac5_fpe_irq_status(void __iomem *ioaddr, struct net_device *dev)
> > >  	return status;
> > >  }
> > >  
> > > -void dwmac5_fpe_send_mpacket(void __iomem *ioaddr, enum stmmac_mpacket_type type)
> > > +void dwmac5_fpe_send_mpacket(void __iomem *ioaddr, struct stmmac_fpe_cfg *cfg,
> > > +			     enum stmmac_mpacket_type type)
> > >  {
> > > -	u32 value;
> > > +	u32 value = cfg->fpe_csr;
> > >  
> > > -	value = readl(ioaddr + MAC_FPE_CTRL_STS);
> > > -
> > > -	if (type == MPACKET_VERIFY) {
> > > -		value &= ~SRSP;
> > > +	if (type == MPACKET_VERIFY)
> > >  		value |= SVER;
> > > -	} else {
> > > -		value &= ~SVER;
> > > +	else if (type == MPACKET_RESPONSE)
> > >  		value |= SRSP;
> > > -	}
> > >  
> > >  	writel(value, ioaddr + MAC_FPE_CTRL_STS);
> > >  }
> > 
> 
> > It's unclear to me why it's not necessary to preserve the SVER/SRSP
> > bits across MAC_FPE_CTRL_STS writes. I guess they are not part of the
> > status bits? perhaps an explicit comment somewhere will help?
> 
> The SRSP and SVER are self-cleared flags with no effect on zero
> writing. Their responsibility is to emit the Respond and Verify
> mPackets respectively. As soon as the packets are sent, the flags will
> be reset by hardware automatically. So no, they aren't a part of the
> status bits.
> 
> Note since 'value' now isn't read from the MAC_FPE_CTRL_STS register,
> there is no point in clearing up these flags in the local variable
> because 'value' has now them cleared by default.
> 
> Not sure whether a comment about that is required, since the described
> behavior is well documented in the Synopsys HW-manual.

Thanks for the explanation, it clarifies the things to me. I agree
there is no need for a patch change.

Cheers,

Paolo


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