netdev - Re: [PATCH 5/7] net: stmmac: Program RX queue size and flow control

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Message-ID: <20170309194231.GD5554@ulmo.ba.sec>
Date:   Thu, 9 Mar 2017 20:42:31 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Mikko Perttunen <cyndis@...si.fi>
Cc:     "David S . Miller" <davem@...emloft.net>,
        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 Mon, Feb 27, 2017 at 12:09:02PM +0200, Mikko Perttunen wrote:
> 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.

I'll investigate. To be honest I simply took this from Stephen's U-Boot
driver since that's already tested. I trust Stephen, so I didn't bother
double-checking.

Thierry

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