linux-kernel - Re: [PATCH] cpsw: Fix interrupt storm among other things

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Message-Id: <0FB10FF4-6639-472E-943C-61CEDB0336E0@antoniou-consulting.com>
Date:	Wed, 30 Jan 2013 11:36:20 +0200
From:	Pantelis Antoniou <panto@...oniou-consulting.com>
To:	Mugunthan V N <mugunthanvnm@...com>
Cc:	Richard Cochran <richardcochran@...il.com>,
	Matt Porter <mporter@...com>,
	Chase Maupin <chase.maupin@...com>, Jason Kridner <jdk@...com>,
	Tony Lindgren <tony@...mide.com>, <linux-omap@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpsw: Fix interrupt storm among other things

Hi,

On Jan 30, 2013, at 11:03 AM, Mugunthan V N wrote:

> On 1/30/2013 2:06 PM, Pantelis Antoniou wrote:
>> Hi Mugunthan,
>> 
>> On Jan 29, 2013, at 1:45 PM, Mugunthan V N wrote:
>> 
>>> On 1/28/2013 6:41 PM, Pantelis Antoniou wrote:
>>>> Fix interrupt storm on bone A4 cause by non-by-the-book interrupt handling.
>>>> While at it, added a non-NAPI mode (which is easier to debug), plus
>>>> some general fixes.
>>>> 
>>>> Signed-off-by: Pantelis Antoniou <panto@...oniou-consulting.com>
>>>> ---
>>>>  Documentation/devicetree/bindings/net/cpsw.txt |   1 +
>>>>  drivers/net/ethernet/ti/cpsw.c                 | 222 +++++++++++++++++++++----
>>>>  drivers/net/ethernet/ti/davinci_cpdma.c        |   4 +-
>>>>  drivers/net/ethernet/ti/davinci_cpdma.h        |   2 +-
>>>>  include/linux/platform_data/cpsw.h             |   1 +
>>>>  5 files changed, 194 insertions(+), 36 deletions(-)
>>> I have tested CPSW on AM335x EVM 1.5A with flood ping and i am not
>>> seeing any interrupt storm.
>>> Can you provide more details on how to reproduce the issue.
>>> 
>> A beaglebone prototype with the new silicon version, with the ethernet errata
>> fixed displays this. You can't trigger it on old silicon.
>> 
>> The TI people on the CC list can confirm.
> But i have the same silicon revision (PG2.0) in my EVM and I am not seeing any issues. Can you
> point me to the ethernet errata which you are mentioning?
> 
> Regards
> Mugunthan V N

What kernel version are you using? This is only triggered on the mainline driver.

The advisory in question: From http://www.ti.com/lit/er/sprz360c/sprz360c.pdf 

Advisory 1.0.9: "Ethernet Media Access Controller and Switch Subsystem: C0_TX_PEND 
and C0_RX_PEND Interrupts Not Connected to ARM Cortex-A8"

I bet you're using an old kernel driver with the workarounds with the timers.

If I had to guess (although I didn't use a probe or anything) is that the
interrupts are now proper level interrupts, instead of working in edge
triggered mode due to the workaround. 

Apparently the interrupt was never acked properly in the original driver 
(the sequence described in the TRM is not followed).

Looking at the TRM (spruh73g.pdf) 14.3.1.3 Interrupts in particular, the
the status registers are not read, and more damning the proper values to the 
CPDMA_EOI_VECTOR register are not written.

The original driver blindly wrote zero (cpdma_ctlr_eoi), while you have to
write different values according to the interrupt you ack.

What happened was that on the first interrupt, the interrupt was never acked,
and we had an irq storm...

Regards

-- Pantelis




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