linux-kernel - Re: [PATCH][RT] 2.6.24-rc2-rt1 drivers/dma/ioat

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Date:	Fri, 16 Nov 2007 09:07:29 -0800
From:	"Nelson, Shannon" <shannon.nelson@...el.com>
To:	<linux-rt-users@...r.kernel.org>, <Linux-kernel@...r.kernel.org>,
	"Sven-Thorsten Dietrich" <sdietrich@...ell.com>
Subject: Re: [PATCH][RT] 2.6.24-rc2-rt1 drivers/dma/ioat_dma.c compile fix

On Nov 16, 2007 3:57 AM, Sven-Thorsten Dietrich <sdietrich@...ell.com>
wrote:
> Compile fix for new code in -rc2.
> 
> I'm not positive about the insertion point...
> 
> Subject: compile error fix (needs review)
> 
> RT changes __list_splice to require prev and next pointers.
> 
> This changes the use in the new code to list_splice_tail,
> but the optimal insertion point needs to be analyzed.
> 
> Signed-off-by: Sven-Thorsten Dietrich <sdietrich@...e.de>
> 
> ---
>  drivers/dma/ioat_dma.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6.23/drivers/dma/ioat_dma.c
> ===================================================================
> --- linux-2.6.23.orig/drivers/dma/ioat_dma.c
> +++ linux-2.6.23/drivers/dma/ioat_dma.c
> @@ -244,7 +244,7 @@ static dma_cookie_t ioat_tx_submit(struc
>         /* write address into NextDescriptor field of last desc in
chain */
>         to_ioat_desc(ioat_chan->used_desc.prev)->hw->next =
>
first->async_tx.phys;
> -       __list_splice(&new_chain, ioat_chan->used_desc.prev);
> +       list_splice_tail(&new_chain, ioat_chan->used_desc.prev);
> 

NAK.

These functions do insertions differently.  The 'prev' is pointing to
the last valid descriptor in the queue and you really want to get the
new_chain stuck on after this.  Your list_splice_tail() will insert the
new_chain just before it which will muck up the order of the DMA
requests.

You might have more success with
	list_splice_tail(&new_chain, ioat_chan->used_desc);
where used_desc points to the whole list, rather than using the .prev
pointer to a specific node.

Please copy me on future ioatdma related comments.

Thanks,
sln
--
======================================================================
Mr. Shannon Nelson                 LAN Access Division, Intel Corp.
Shannon.Nelson@...el.com                I don't speak for Intel
(503) 712-7659                    Parents can't afford to be squeamish.
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