Date:	Mon, 28 Jan 2013 12:47:32 -0700
From:	Troy Kisky <troy.kisky@...ndarydevices.com>
To:	Vikram Narayanan <vikram186@...il.com>
CC:	netdev@...r.kernel.org, Greg Ungerer <gregungerer@...tnet.com.au>,
	shawn.guo@...aro.org, LAK <linux-arm-kernel@...ts.infradead.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Subject: Re: i.Mx6Quad - eth0: tx queue full!

On 1/28/2013 10:39 AM, Vikram Narayanan wrote:
> Running the latest head <linux-2.6.git> on an i.Mx6Quad based platform
> gives me the below error when flooded with ping requests.
>
> == Start log ==
> [ 2555.004031] ------------[ cut here ]------------
> [ 2555.009740] WARNING: at net/sched/sch_generic.c:254 dev_watchdog+0x298/0x2b8()
> [ 2555.018721] NETDEV WATCHDOG: eth0 (fec): transmit queue 0 timed out

I think the tx interrupt status bit was lost. The packets were 
transmitted, but the interrupt never
happened. The controller should have been reset here, but perhaps a bug 
with the reset code.
Are you using the mainline kernel, or a version Freescale's kernel.

mainline fec_restart does not reset tx_full

You can try adding
fep->tx_full = 0;

to fec_restart, though it would be better to call fec_enet_tx in fec_timeout
and skip the call to fec_restart if it returns some packets.

> [ 2555.026733] Modules linked in:
> [ 2555.030598] Backtrace:
> [ 2555.034252] [<800119c8>] (dump_backtrace+0x0/0x10c) from [<803b8494>] (dump_stack+0x18/0x1c)
> [ 2555.044438]  r6:000000fe r5:80302f64 r4:80503dd0 r3:80510e80
> [ 2555.052019] [<803b847c>] (dump_stack+0x0/0x1c) from [<8001df08>] (warn_slowpath_common+0x54/0x6c)
> [ 2555.062679] [<8001deb4>] (warn_slowpath_common+0x0/0x6c) from [<8001dfc4>] (warn_slowpath_fmt+0x38/0x40)
> [ 2555.073936]  r8:8052ebf1 r7:805040c0 r6:00000000 r5:8f9771d4 r4:8f977000
> r3:00000009
> [ 2555.084816] [<8001df8c>] (warn_slowpath_fmt+0x0/0x40) from [<80302f64>] (dev_watchdog+0x298/0x2b8)
> [ 2555.095535]  r3:8f977000 r2:8049f6d4
> [ 2555.099868] [<80302ccc>] (dev_watchdog+0x0/0x2b8) from [<8002acf8>] (call_timer_fn.isra.33+0x2c/0x8c)
> [ 2555.110794] [<8002accc>] (call_timer_fn.isra.33+0x0/0x8c) from [<8002af48>] (run_timer_softirq+0x1f0/0x204)
> [ 2555.122240]  r7:80571114 r6:805040c0 r5:00000000 r4:80570900
> [ 2555.129894] [<8002ad58>] (run_timer_softirq+0x0/0x204) from [<80025750>] (__do_softirq+0xc8/0x180)
> [ 2555.140599] [<80025688>] (__do_softirq+0x0/0x180) from [<80025b40>] (irq_exit+0x88/0x90)
> [ 2555.150492] [<80025ab8>] (irq_exit+0x0/0x90) from [<8000ec58>] (handle_IRQ+0x44/0x98)
> [ 2555.160112]  r4:804ffde0 r3:00000220
> [ 2555.164848] [<8000ec14>] (handle_IRQ+0x0/0x98) from [<80008540>] (gic_handle_irq+0x30/0x64)
> [ 2555.174956]  r6:80503f28 r5:8050a518 r4:f400010c r3:00000000
> [ 2555.182694] [<80008510>] (gic_handle_irq+0x0/0x64) from [<8000df80>] (__irq_svc+0x40/0x50)
> [ 2555.192737] Exception stack(0x80503f28 to 0x80503f70)
> [ 2555.198639] 3f20:                   8052f150 a0000093 00000000 00000000 80502000 8052ed08
> [ 2555.208600] 3f40: 8050a4f4 803bfaec 8050df00 412fc09a 80502000 80503f7c 80503f80 80503f70
> [ 2555.218584] 3f60: 8000eee4 8000eee8 60000013 ffffffff
> [ 2555.224730]  r7:80503f5c r6:ffffffff r5:60000013 r4:8000eee8
> [ 2555.232292] [<8000eeb8>] (default_idle+0x0/0x38) from [<8000f0d8>] (cpu_idle+0xcc/0x114)
> [ 2555.242204] [<8000f00c>] (cpu_idle+0x0/0x114) from [<803b3718>] (rest_init+0x64/0x7c)
> [ 2555.251858] [<803b36b4>] (rest_init+0x0/0x7c) from [<804cc7dc>] (start_kernel+0x258/0x298)
> [ 2555.261963] [<804cc584>] (start_kernel+0x0/0x298) from [<10008078>] (0x10008078)
> [ 2555.271167] ---[ end trace 3d2ffb53e6fe41f3 ]---
> [ 2555.277270] eth0: tx queue full!.
> [ 2555.288776] eth0: tx queue full!.
> [ 2555.293594] eth0: tx queue full!.
> [ 2555.297944] eth0: tx queue full!.
> [ 2555.302229] eth0: tx queue full!.
All the packet have been transmitted but the transmit queue is full, so 
no more
tx interrupts can happen to replace the previously lost tx interrupt.

I've seen MII interrupts clear the TX interrupt status bit.

> ...... continues indefinitely and needs a reboot to recover the system.
> == End log ==
>
> i.Mx6Quad's MAC is connected to SMSC LAN88730 PHY via an MII interface.
>
> I found a similar thread [1], but that solution didn't work for me.
> Any ideas on why the fec driver is unhappy?
>
> Thanks,
> Vikram
>
> [1] https://community.freescale.com/thread/281457
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>

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