Re: [PATCH v6 0/2] Ethernet drivers for WIZnet chips

[Mike Sinkovsky]

03.04.2012 18:29, Eric Dumazet ÐÐÐÐÑÐÐ:
> On Tue, 2012-04-03 at 18:15 +0600, Mike Sinkovsky wrote:
> > 03.04.2012 17:39, Eric Dumazet ÐÐÐÐÑÐÐ:
> > > On Tue, 2012-04-03 at 16:58 +0600, Mike Sinkovsky wrote:
> > > > Based on original driver from chip manufacturer, but nearly full rewite.
> > > > Tested and used in production with Blackfin BF531 embedded processor.
> > > >
> > > > Signed-off-by: Mike Sinkovsky<msink@xxxxxxxxxxxxx>
> > > > ---
> > > > v6:
> > > >    - remove (S0_TX_FSR<   skb->len) check in TX handler, it doesn't work
> > > >      anyway. Chip can transmit only one frame with MTU 1500 at a time,
> > > >      and tx buffer size is bigger.
> > >
> > > So what happens if XXX frames are given to start_xmit() in a flood ?
> > >
> > > You removed any flow control, how can this work ?
> > >
> > > Device has an infinite queue ?
> >
> > As I understand from datasheet, device doesn't have tx queue at all.
> > It have tx buffer, processor must save transmitted frame to it, and then
> > save SEND command to command register. When transmission completed,
> > SENDOK bit in interrupt register will be set to '1', and interrupt
> > handler will be called.
> >
> > So, according to datasheet, driver must stop queue in start_xmit()
> > routine, and wake in interrupt handler of SENDOK bit.
> > I tried this, and it basically works, but SOMETIMES, very rare, I see
> > tx_timeout().
> >
> > And without any flow control - driver works perfectly.
> > Weird, don't know why.
>
> Really this should be fixed, since your driver makes qdisc flow control
> impossible (unless adding a rate limiter like HTB/CBQ)
>
> You probably had a race on your xmit routine, and interrupt routine.
>
> You need proper synchronization : A spinlock to make this easy, or a
> smart barrier game.

I can at least make it configurable from Kconfig with default 'y', and 
disable for our boards.
Would it be acceptable?

About races - I can't see any, in this very simple procedure.
But maybe I missed something..


--
Mike

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