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Date:   Mon, 27 Feb 2017 12:09:02 +0200
From:   Mikko Perttunen <cyndis@...si.fi>
To:     Thierry Reding <thierry.reding@...il.com>,
        "David S . Miller" <davem@...emloft.net>
Cc:     Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Alexandre Courbot <gnurou@...il.com>,
        Jon Hunter <jonathanh@...dia.com>, netdev@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7] net: stmmac: Program RX queue size and flow control

On 23.02.2017 19:24, Thierry Reding wrote:
> From: Thierry Reding <treding@...dia.com>
>
> Program the receive queue size based on the RX FIFO size and enable
> hardware flow control for large FIFOs.
>
> Signed-off-by: Thierry Reding <treding@...dia.com>
> ---
>  drivers/net/ethernet/stmicro/stmmac/dwmac4.h     | 12 +++++++
>  drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c | 43 ++++++++++++++++++++++--
>  2 files changed, 53 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4.h b/drivers/net/ethernet/stmicro/stmmac/dwmac4.h
> index db45134fddf0..9acc1f1252b3 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac4.h
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4.h
> @@ -180,6 +180,7 @@ enum power_event {
>  #define MTL_OP_MODE_TSF			BIT(1)
>
>  #define MTL_OP_MODE_TQS_MASK		GENMASK(24, 16)
> +#define MTL_OP_MODE_TQS_SHIFT		16
>
>  #define MTL_OP_MODE_TTC_MASK		0x70
>  #define MTL_OP_MODE_TTC_SHIFT		4
> @@ -193,6 +194,17 @@ enum power_event {
>  #define MTL_OP_MODE_TTC_384		(6 << MTL_OP_MODE_TTC_SHIFT)
>  #define MTL_OP_MODE_TTC_512		(7 << MTL_OP_MODE_TTC_SHIFT)
>
> +#define MTL_OP_MODE_RQS_MASK		GENMASK(29, 20)
> +#define MTL_OP_MODE_RQS_SHIFT		20
> +
> +#define MTL_OP_MODE_RFD_MASK		GENMASK(19, 14)
> +#define MTL_OP_MODE_RFD_SHIFT		14
> +
> +#define MTL_OP_MODE_RFA_MASK		GENMASK(13, 8)
> +#define MTL_OP_MODE_RFA_SHIFT		8
> +
> +#define MTL_OP_MODE_EHFC		BIT(7)
> +
>  #define MTL_OP_MODE_RTC_MASK		0x18
>  #define MTL_OP_MODE_RTC_SHIFT		3
>
> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
> index 8d249f3b34c8..03d230201960 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
> @@ -185,8 +185,9 @@ static void dwmac4_rx_watchdog(void __iomem *ioaddr, u32 riwt)
>  }
>
>  static void dwmac4_dma_chan_op_mode(void __iomem *ioaddr, int txmode,
> -				    int rxmode, u32 channel)
> +				    int rxmode, u32 channel, int rxfifosz)
>  {
> +	unsigned int rqs = rxfifosz / 256 - 1;
>  	u32 mtl_tx_op, mtl_rx_op, mtl_rx_int;
>
>  	/* Following code only done for channel 0, other channels not yet
> @@ -252,6 +253,44 @@ static void dwmac4_dma_chan_op_mode(void __iomem *ioaddr, int txmode,
>  			mtl_rx_op |= MTL_OP_MODE_RTC_128;
>  	}
>
> +	mtl_rx_op &= ~MTL_OP_MODE_RQS_MASK;
> +	mtl_rx_op |= rqs << MTL_OP_MODE_RQS_SHIFT;
> +
> +	/* enable flow control only if each channel gets 4 KiB or more FIFO */
> +	if (rxfifosz >= 4096) {
> +		unsigned int rfd, rfa;
> +
> +		mtl_rx_op |= MTL_OP_MODE_EHFC;
> +
> +		switch (rxfifosz) {
> +		case 4096:
> +			rfd = 0x03;
> +			rfa = 0x01;
> +			break;
> +
> +		case 8192:
> +			rfd = 0x06;
> +			rfa = 0x0a;
> +			break;
> +
> +		case 16384:
> +			rfd = 0x06;
> +			rfa = 0x12;
> +			break;
> +
> +		default:
> +			rfd = 0x06;
> +			rfa = 0x1e;
> +			break;
> +		}

Are these values correct? In the 4096 case, rfd > rfa, in all other 
cases the other way around. In any case it would be useful to have a 
comment clarifying the thresholds in bytes.

> +
> +		mtl_rx_op &= ~MTL_OP_MODE_RFD_MASK;
> +		mtl_rx_op |= rfd << MTL_OP_MODE_RFD_SHIFT;
> +
> +		mtl_rx_op &= ~MTL_OP_MODE_RFA_MASK;
> +		mtl_rx_op |= rfa << MTL_OP_MODE_RFA_SHIFT;
> +	}
> +
>  	writel(mtl_rx_op, ioaddr + MTL_CHAN_RX_OP_MODE(channel));
>
>  	/* Enable MTL RX overflow */
> @@ -264,7 +303,7 @@ static void dwmac4_dma_operation_mode(void __iomem *ioaddr, int txmode,
>  				      int rxmode, int rxfifosz)
>  {
>  	/* Only Channel 0 is actually configured and used */
> -	dwmac4_dma_chan_op_mode(ioaddr, txmode, rxmode, 0);
> +	dwmac4_dma_chan_op_mode(ioaddr, txmode, rxmode, 0, rxfifosz);
>  }
>
>  static void dwmac4_get_hw_feature(void __iomem *ioaddr,
>

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