Re: [PATCH][1/2] usb: dma bounce buffer support V3

[Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>]

On Tue, 22 Jan 2008 15:12:53 +0900 "Magnus Damm" <magnus.damm@xxxxxxxxx> wrote:

> On Jan 22, 2008 2:01 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > On Tue, 22 Jan 2008 12:20:10 +0900 Magnus Damm <magnus.damm@xxxxxxxxx> wrote:
> >
> > > usb: dma bounce buffer support V3
> > >
> > > This patch adds dma bounce buffer support to the usb core. These buffers
> > > can be enabled with the HCD_LOCAL_MEM flag, and they make sure that all data
> > > passed to the host controller is allocated using dma_alloc_coherent().
> >
> > It is unobvious (to me) why this code uses put_unaligned() and
> > get_unaligned() in the places where it does.  So I'll assume that it will
> > be unobvious to other reviewers and readers.
> 
> The HCD_LOCAL_MEM dma bounce buffer code is using unaligned functions
> to temporarily save a pointer at the end of the dma data buffer.
> hcd_alloc_coherent() saves the pointer which is needed by
> hcd_free_coherent(). The unaligned functions are used because the size
> of the buffer may be uneven.
> 
> It's of course possible to round up the size instead and use aligned
> access if you prefer that. The memory area used for dma may be limited
> though so I felt it was natural to optimize for small memory footprint
> over access speed.

that wasn't a patch ;)

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