linux-kernel - Re: [patch 1/5] Staging: VME Framework for the Linux Kernel

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Message-ID: <20090810195048.GB3055@braap.org>
Date:	Mon, 10 Aug 2009 21:50:48 +0200
From:	"Emilio G. Cota" <cota@...ap.org>
To:	Martyn Welch <martyn.welch@...anuc.com>
Cc:	Greg K-H <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org,
	Sebastien Dugue <sebastien.dugue@...l.net>
Subject: Re: [patch 1/5] Staging: VME Framework for the Linux Kernel

Martyn Welch wrote:
> If the driver writer wants a "single shot" effect, there's little  
> overhead in creating a one item link-list and executing it. However,  
> without support for this mode the author is stuck with single shot  
> transfers.  If the author wants to perform scatter gather type  
> transfers, without this functionality in the API - which is supported by  
> all the bridges I have seen - he won't be able to easily avail himself  
> of this functionality and get "work done".

Again, he (the driver writer) should know *nothing* about that.

As for the scatter-gather case, what should happen is:

User:		hey, there's a buffer I want to transfer. here's
		a pointer and size
VME layer:	ok, passing it to the bridge
VME bridge:	I know I'm over PCI, so I'll get the pages
		from memory and map the sg list over PCI, and
		then will tell the bridge to perform from there.

That's just a particular example, but for the user (read driver
writer) it's much simpler this way. Doesn't need to know about
lists or whatever.

E.
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