linux-kernel - Re: [PATCH] enhanced reimplemented of the kfifo API

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Message-ID: <1263593107.8935.1.camel@wall-e>
Date:	Fri, 15 Jan 2010 23:05:07 +0100
From:	Stefani Seibold <stefani@...bold.net>
To:	"Ira W. Snyder" <iws@...o.caltech.edu>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Theodore Tso <tytso@....edu>
Subject: Re: [PATCH] enhanced reimplemented of the kfifo API

Am Freitag, den 15.01.2010, 14:01 -0800 schrieb Ira W. Snyder:
> On Fri, Jan 15, 2010 at 10:30:01PM +0100, Stefani Seibold wrote:
> > 
> > > I'm glad to see this example, it really illustrates how to use the new
> > > DMA functionality of the kfifo API.
> > > 
> > > Is there any reason why a very large scatterlist could not be used? I
> > > have a driver that uses a large scatterlist (~4000 entries, allocated as
> > > a struct sg_table). I implemented my own copy_from_user() functionality
> > > into this scatterlist, but I'd love to use the kfifo DMA API instead.
> > > After filling the scatterlist, I use the usual DMA API's to transfer it
> > > to my device.
> > > 
> > 
> > No, but the API will only return max. two entries.
> > 
> 
> Ah, I see. __kfifo_alloc() uses kmalloc() internally. The kfifo API will
> not work for my purposes then, since I want to allocate a 16MB chunk of
> memory, and I'm very uncomfortable doing that with kmalloc(). I'll stick
> with my custom scatterlist code, which uses alloc_page() to fill in the
> scatterlist with order-0 allocations.
> 

I think you can use vmalloc() instead and assign this buffer with
kfifo_init().

> Another nitpick in the code: I've noticed that you use sgl++ in the
> setup_sgl() function. That should become "sgl = sg_next(sgl);" so that
> this code can work with an struct sg_table as well.

No, its by definition an array. You cannot pass as struct sg_table to
the kfifo_dma_* functions.

Stefani


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