netdev - Re: [PATCH] sky2: Fix WARNING: at lib/dma-debug.c:902 check

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Date:	Wed, 20 Jan 2010 23:53:22 +0100
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	David Miller <davem@...emloft.net>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	Michael Breuer <mbreuer@...jas.com>, akpm@...ux-foundation.org,
	flyboy@...il.com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, Michael Chan <mchan@...adcom.com>,
	Don Fry <pcnet32@...izon.net>,
	Francois Romieu <romieu@...zoreil.com>,
	Matt Carlson <mcarlson@...adcom.com>
Subject: Re: [PATCH] sky2: Fix WARNING: at lib/dma-debug.c:902 check_sync

On Wed, Jan 20, 2010 at 10:24:14PM +0000, Alan Cox wrote:
> > > Seems like an underlying bug in the DMA api. Maybe it just can't
> > > handle operations on partial mapping.
> > > 
> > > Other drivers with same problem:
> > >   bnx2, cassini, pcnet32, r8169, rrunner, skge, sungem, tg3, 
> > 
> > It seems using the same length (even without pci_unmap_len()) is
> > crucial here, but I hope maintainers (added to CC) will take care.
> 
> The API needs fixing - if you've got a large mapping and you want to sync
> part of it then we need to support that. Now it might well be that the
> implementation on some braindead platform has to sync the entire thing,
> and some implementations entire pages or cache lines.
> 
> You can't fix this in the drivers, they requested a service and they
> don't have enough information nor is it their job to know about all the
> platform specific rules.

Yes, the need to repeat some other values if there is a dedicated
structure/pointer could be misleading. Btw, it seems to be a trivial
overlooking since there is dma_sync_single_range() ready to use.

Jarek P.
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