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    SubjectRe: [PATCH v6 0/2] Ethernet drivers for WIZnet chips
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    On Tue, 2012-04-03 at 18:15 +0600, Mike Sinkovsky wrote:
    > 03.04.2012 17:39, Eric Dumazet написал:
    > > 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@permonline.ru>
    > >> ---
    > >> 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.



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