netdev - Re: eHEA driver issues from net-2.6.24

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Date:	Wed, 22 Aug 2007 15:03:02 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	habanero@...ibm.com
Cc:	ossthema@...ibm.com, netdev@...r.kernel.org
Subject: Re: eHEA driver issues from net-2.6.24

From: Andrew Theurer <habanero@...ibm.com>
Date: Wed, 22 Aug 2007 16:55:03 -0500

Thanks for finally getting to test this, I thought nobody
would test this until it got merged into 2.6.24 :-/

> kernel BUG at include/linux/netdevice.h:318!
> enter ? for help
> [c00000000f613e40] c0000000003fe394 .net_rx_action+0x1b8/0x254
> [c00000000f613ef0] c000000000057b70 .__do_softirq+0xa8/0x164
> [c00000000f613f90] c000000000024438 .call_do_softirq+0x14/0x24
> [c000000b8ffbf9f0] c00000000000bd30 .do_softirq+0x68/0xac
> [c000000b8ffbfa80] c000000000057cc4 .irq_exit+0x54/0x6c
> [c000000b8ffbfb00] c00000000000c358 .do_IRQ+0x170/0x1ac
> [c000000b8ffbfb90] c000000000004780 hardware_interrupt_entry+0x18/0x98
> --- Exception: 501 (Hardware Interrupt) at c000000000010bdc 
> .cpu_idle+0x114/0x1e0
> [c000000b8ffbfe80] c000000000010bd0 .cpu_idle+0x108/0x1e0 (unreliable)
> [c000000b8ffbff00] c000000000026db0 .start_secondary+0x160/0x184
> [c000000b8ffbff90] c000000000008364 .start_secondary_prolog+0xc/0x10
>
> I'm a little confused if the port_napi_enable() is being called when the 
> device is initialized, but then again, this is all new to me (should it 
> be called in ehea_open?).  I see it called on some reset routines, but 
> not on the first initialization.

This is similar to the problem that Arnaldo hit a few minutes
ago in the VIA Rhine driver.

You can't only make a napi_enable() call when there has been
a previous napi_disable().

One way to fix this would be to forcefully napi_disable() on
all the per-port NAPI structs at the beginning of ehea_open(),
which should set things up to satisfy the pre-condition of the
napi_enable() calls.

You'll need to audit the entire driver to make sure this invariant
is held properly.

> Also, on this code, in ehea_sense_port_attr()
> 
> /* Number of default QPs */
>         if (use_mcs)
>                 port->num_def_qps = cb0->num_default_qps;
>         else
>                 port->num_def_qps = 1;
>                
> 
> When using napi, since we have multi-queue napi support now, wouldn't we 
> want to use all the default qps instead of 1?

I don't know how this hardware works, you tell me :-)
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