Re: [PATCH net v2] net: stmmac: Set MAC's flow control register to reflect current settings

From: Russell King (Oracle)
Date: Tue Nov 22 2022 - 13:54:19 EST


On Tue, Nov 22, 2022 at 06:40:33PM +0000, Russell King (Oracle) wrote:
> On Tue, Nov 22, 2022 at 02:39:35PM +0800, Goh, Wei Sheng wrote:
> > diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> > index c25bfecb4a2d..369db308b1dd 100644
> > --- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> > +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> > @@ -748,6 +748,9 @@ static void dwmac4_flow_ctrl(struct mac_device_info *hw, unsigned int duplex,
> > if (fc & FLOW_RX) {
> > pr_debug("\tReceive Flow-Control ON\n");
> > flow |= GMAC_RX_FLOW_CTRL_RFE;
> > + } else {
> > + pr_debug("\tReceive Flow-Control OFF\n");
> > + flow &= ~GMAC_RX_FLOW_CTRL_RFE;
> > }
> > writel(flow, ioaddr + GMAC_RX_FLOW_CTRL);
>
> This doesn't look correct to me. The function starts off:
>
> unsigned int flow = 0;
>
> flow is not written to before the context above. So, the code you've
> added effectively does:
>
> flow = 0 & ~GMAC_RX_FLOW_CTRL_RFE;
>
> which is still zero. So, I don't think this hunk is meaningful apart
> from adding the pr_debug().

It also should be noted that it looks like:

dwxgmac2_core.c::dwxgmac2_flow_ctrl() is definitely buggy - it will
only set flow control, never clearing it.

dwmac100_core.c::dwmac100_flow_ctrl() looks potentially buggy - always
enabling flow control irrespective of anything.

The other two implmentations look sane to me.

--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!