Messages in this thread | | | Date | Wed, 04 Apr 2012 11:58:35 +0600 | From | Mike Sinkovsky <> | Subject | Re: [PATCH v6 0/2] Ethernet drivers for WIZnet chips |
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03.04.2012 18:29, Eric Dumazet написал: > 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.
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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