Messages in this thread | | | Date | Wed, 20 Jan 2010 14:50:10 -0800 (PST) | Subject | Re: [PATCH] sky2: Fix WARNING: at lib/dma-debug.c:902 check_sync | From | David Miller <> |
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From: Jarek Poplawski <jarkao2@gmail.com> Date: Wed, 20 Jan 2010 21:58:42 +0100
> Yes, and it's mainly for lib/dma-debug (until it's not verified dmar > errors reported by Michael Breuer could be connected). So, I'm not > sure for now how serious this warning could be. On the other hand, > Documentation/(PCI-?)DMA-mapping, mentioned by Stephen, doesn't seem > to allow or use in examples the "size" different than mapped.
Someone find me even one actual implemenetation of the DMA APIs, not the debugging code, which can't handle a partial sync correctly, then we can talk.
As the person who originally created the PCI DMA APIs I can tell you the intention was definitely to allow arbitrary SYNC lengths and there was no requirement that the length needed to be the same as that used in the mapping call.
Nothing else makes sense. People sync when they have a partially used buffer and want to copy the data out then recycle the big original buffer back to the chip. I knew this when creating the PCI DMA APIs because I first tried to use them in network drivers and that's what so many of them do.
Currently all we have is an overly anal DMA debugging layer check, and some speculation that it might or might not fix some real bug.
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