Re: [PATCH 1/4] block: use ARCH_KMALLOC_MINALIGN as the default dma pad mask

[FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>]

On Wed, 21 May 2008 21:46:24 +0900
FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> wrote:

> On Wed, 21 May 2008 20:22:18 +0800
> Herbert Xu <herbert@gondor.apana.org.au> wrote:
> 
> > On Wed, May 21, 2008 at 09:09:58PM +0900, FUJITA Tomonori wrote:
> > >
> > > OK, thanks. So it's about hardware requrement. Let me make sure if I
> > > understand crypto alignment issue.
> > > 
> > > __crt_ctx needs ARCH_KMALLOC_MINALIGN alignment only because of crypto
> > > hardware. If I misunderstand it, can you answer my question in the
> > > previous mail (it's the part that you cut)? That is, why does
> > > __crt_ctx need ARCH_KMALLOC_MINALIGN alignment with software
> > > algorithms.
> > 
> > Because the same structure is used for all algorithms!
> 
> No, you misunderstand my question. I meant, software algorithms don't
> need ARCH_KMALLOC_MINALIGN alignment for __crt_ctx and if we are fine
> with using the ALIGN hack for crypto hardware every time (like
> aes_ctx_common), crypto doesn't need ARCH_KMALLOC_MINALIGN alignment
> for __crt_ctx. Is this right?
> 
> 
> > 
> > Why is this so hard to understand?
> 
> Because there are few architecture that defines
> ARCH_KMALLOC_MINALIGN. So if crypto hardware needs alignement, it's
> likely the hardware alignement is larger than __crt_ctx alignment. As
> a result, you have to use ALIGN_PTR. So It's hard to understand using
> ARCH_KMALLOC_MINALIGN here. I don't know about crypto hardware, but I
> wonder if we can use a static alignment like 64 bytes here, which may
> work for most of crypto hardware. Or if there are not many users of

Oops, scratch the static alignment. It's impossible.


> crypto hardware, it may be fine to use ALIGN_PTR for the hardware.

I still wonder it's acceptable or not.

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