netdev - Re: [PATCH] 8139cp: set ring address after enabling C+ mode

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Date:	Thu, 22 Nov 2012 23:12:53 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	Francois Romieu <romieu@...zoreil.com>
Cc:	Jeff Garzik <jgarzik@...ox.com>,
	David Miller <davem@...emloft.net>, jasowang@...hat.com,
	netdev@...r.kernel.org, slacky@...apnet.it, rggjan@...il.com,
	gilboad@...il.com, Hayes Wang <hayeswang@...ltek.com>
Subject: Re: [PATCH] 8139cp: set ring address after enabling C+ mode

On Thu, 2012-11-22 at 22:39 +0100, Francois Romieu wrote:
> Btw David W., could consider adding artificial delays between the
> writes and see if / when things start to fail (CpCmd write in
> cp_start_hw is an unflushed posted write for instance).

That's how I tracked it down to the CpCmd write. I littered the whole of
the init path with
 printk("at line %d TxRingAddr %08x%08 (sb %08x)\n", __LINE__,
         cpr32(TxRingAddr+4), cpr32(TxRingAddr), cp->ring_dma + whatever);
... until the output looked something like this:

root@...s:~# insmod ./8139cp.ko 
[ 1331.492486] 8139cp: 8139cp: 10/100 PCI Ethernet driver v1.3 (Mar 22, 2004)
[ 1331.500388] 8139cp 0000:00:0a.0: eth0: RTL-8139Cx at 0xd10a6000, 00:0a:fa:22:
00:96, IRQ 10
[ 1331.509608] 8139cp 0000:00:0b.0: eth1: RTL-8139Cx at 0xd10a8100, 00:0a:fa:22:
00:97, IRQ 11
root@...s:~# [ 1331.644393] at line 995 TxRingAddr   000000000f3c6400 (sb f3c6400)
[ 1331.650579] at line 960 TxRingAddr   000000000f3c6400 (sb f3c6400)
[ 1331.656820] at line 962 TxRingAddr   000000000f3e4400 (sb f3c6400)
[ 1331.663020] at line 964 TxRingAddr   000000000f3e4400 (sb f3c6400)
[ 1331.669205] at line 998 TxRingAddr   000000000f3e4400 (sb f3c6400)
[ 1331.675412] at line 1001 TxRingAddr   000000000f3e4400 (sb f3c6400)
[ 1331.681706] at line 1003 TxRingAddr   000000000f3e4400 (sb f3c6400)
[ 1331.687977] at line 1005 TxRingAddr   000000000f3e4400 (sb f3c6400)

Each of those printks will have effectively flushed any prior posted
writes... not that this AMD Geode platform actually *does* post writes,
to my knowledge. And at 115200 baud, each one was about a 6ms delay.

-- 
dwmw2


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