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Date: Wed, 20 Jan 2010 23:53:22 +0100
From: Jarek Poplawski <jarkao2@gmail.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: David Miller <davem@davemloft.net>,
       Stephen Hemminger <shemminger@linux-foundation.org>,
       Michael Breuer <mbreuer@majjas.com>, akpm@linux-foundation.org,
       flyboy@gmail.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
       Michael Chan <mchan@broadcom.com>, Don Fry <pcnet32@verizon.net>,
       Francois Romieu <romieu@fr.zoreil.com>,
       Matt Carlson <mcarlson@broadcom.com>
Subject: Re: [PATCH] sky2: Fix WARNING: at lib/dma-debug.c:902 check_sync
Message-ID: <20100120225322.GC3072@del.dom.local>
References: <20100120094103.GA6225@ff.dom.local>
 <20100120222414.57909d14@lxorguk.ukuu.org.uk>
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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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