netdev - Re: NIU driver: Sun x8 Express Quad Gigabit Ethernet Adapter

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Date:	Wed, 12 Nov 2008 18:56:48 +0100
From:	Jesper Krogh <jesper@...gh.cc>
To:	David Miller <davem@...emloft.net>
CC:	jdb@...x.dk, netdev@...r.kernel.org
Subject: Re: NIU driver: Sun x8 Express Quad Gigabit Ethernet Adapter

David Miller wrote:
> I am guessing you're running a 32-bit x86 kernel.
> 
> In such a case the driver has to define a local readq()
> and writeq() implementation.
> 
> What I provide for NIU right now reads the upper 32-bits
> then the lower 32-bits of the register.
> 
> Guess what that does?  The packet counters live in the upper
> 32-bits and the MARK bits live in the lower 32-bits of the
> TX_CS register.
> 
> So it first reads the packet counters, and as a side effect that
> clears the MARK bits in the TX_CS register.  So when we read the lower
> 32-bits the MARK bits are always seen as zero.
> 
> BzzaaarT!
> 
> So the following patch should fix this bug.  writeq() should
> be OK as-is, so doesn't need a similar change.
> 
> diff --git a/drivers/net/niu.c b/drivers/net/niu.c
> index 9acb5d7..d8463b1 100644
> --- a/drivers/net/niu.c
> +++ b/drivers/net/niu.c
> @@ -51,8 +51,7 @@ MODULE_VERSION(DRV_MODULE_VERSION);
>  #ifndef readq
>  static u64 readq(void __iomem *reg)
>  {
> -	return (((u64)readl(reg + 0x4UL) << 32) |
> -		(u64)readl(reg));
> +	return ((u64) readl(reg)) | (((u64) readl(reg + 4UL)) << 32);
>  }
>  
>  static void writeq(u64 val, void __iomem *reg)

On my system, I'm not in a position where I can just pull down the 
server and test, but if the above seems plausible that it is the same 
bug I hit using the 10GBitE card, then I'll definately try to test it out.

I sort-of reliably hit the problem after a few day of production on a 16 
core, amd64 system running NFS-server.

Does it seem likely to be the same problem?

Thanks
-- 
Jesper Krogh
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