Re: [PATCH v3] net: stmmac: fix FPE events losing

[Paolo Abeni]

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@xxxxxxxxx>
> Signed-off-by: Jianheng Zhang <jianheng@xxxxxxxxxxxx>
> ---
>  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?

Thanks

Paolo