linux-kernel - Re: [RFC v2 1/2] PCI-Express Non-Transparent Bridge Support

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Message-ID: <CAF8raN4QFnQ+9k_OGEkYexnK=knQESRSbOgsErNiA8z9MXzZ3A@mail.gmail.com>
Date:	Wed, 1 Aug 2012 10:10:00 +0800
From:	Jianbin Kang <kjbmail@...il.com>
To:	Jon Mason <jon.mason@...el.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, linux-pci@...r.kernel.org,
	Dave Jiang <dave.jiang@...el.com>
Subject: Re: [RFC v2 1/2] PCI-Express Non-Transparent Bridge Support

> Actually this is what I'm working on now, using async_tx to replace the
> memcpy.  I believe the changes shouldn't be that significant.
>
> Is the "hardware that can setup dma" you refer to something that does
> not use this interface?
>

Yes, they use this interface, but split 'memcpy_toio' to two operation:
     1. setup dma
     2. wait/poll for the dma to finish.
So maybe it need to provide a generic function 'tx' for different hardwares.

If async_tx is available, it's much better than this 'sync dma/memcpy'.
One problem with async_tx is, it can't detect memcpy error.
If the remote ntb goes down when async_memcpy is in operation, async_tx
will trigger an oops.
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