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List: e1000-devel
Subject: Re: [E1000-devel] [PATCH] e100: Add missing dma sync for proper
From: Ralf Baechle <ralf () linux-mips ! org>
Date: 2008-08-26 22:49:16
Message-ID: 20080826224916.GB8838 () linux-mips ! org
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On Mon, Aug 25, 2008 at 11:55:12PM -0700, David Daney wrote:
> I am running the e100 driver on a MIPS 4KEc system (32 bit mips with
> non-coherent DMA). There was a problem where received packets would
> get 'stuck' for several seconds at a time and then be released all at
> once.
>
> The cause was that if an interrupt were received when no RX packets
> were available, the status for the receive buffer would be stuck in
> the cache, so when the next interrupt arrived the old status value was
> read (indicating no packets available) instead of the new value.
>
> The fix is to call pci_dma_sync_single_for_device on the RX if the
> packet is not available to invalidate the cache so that at the next
> interrupt valid status is returned.
>
> The driver currently calls pci_dma_sync_single_for_cpu before reading
> the status, and this is indeed needed for cases like the R10000 CPU
> where the cache can be polluted by speculative execution, but for most
> machines it is a nop.
>
> The patch was tested on 2.6.17-rc4 on a MIPS 4KEc.
>
> Signed-off-by: David Daney <ddaney@avtrex.com>
Makes sense to me.
Reviewed-by: Ralf Baechle <ralf@linux-mips.org>
Ralf
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