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

David Miller
2008-11-12T12:11:43Z

From: David Miller <davem@davemloft.net>
Date: Wed, 12 Nov 2008 03:52:40 -0800 (PST)

> Ok, Jesper, please try two things for me, leave the debugging patch
> in there for all the tests:
>
> 1) Retrigger the problem (with or without MSI, doesn't matter) but
> add back in that test I asked you to try last week. The one
> where the "if (++rp->mark_counter == rp->mark_freq)" condition
> test in niu_start_xmit() is commented out, so that the
> "mrk |= TX_DESC_MARK;" statement always runs.
>
> Get me the log dump produced by that scenerio.
>
> 2) Next, simply comment out the:
>
> if (unlikely(!(cs & (TX_CS_MK | TX_CS_MMK))))
> goto out;
>
> lines in niu_tx_work().
>
> Let's see what new info we can get out of this.

These tests are still useful for me, so please perform them,
but I think I've found the bug.

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)