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SubjectRe: [PATCH 3/3] csky: Support kernel non-aligned access
Thx Christoph

On Wed, Aug 21, 2019 at 10:17 AM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Tue, Aug 20, 2019 at 08:34:29PM +0800, guoren@kernel.org wrote:
> > From: Guo Ren <ren_guo@c-sky.com>
> >
> > We prohibit non-aligned access in kernel mode, but some special NIC
> > driver needs to support kernel-state unaligned access. For example,
> > when the bus does not support unaligned access, IP header parsing
> > will cause non-aligned access and driver does not recopy the skb
> > buffer to dma for performance reasons.
> >
> > Added kernel_enable & user_enable to control unaligned access and
> > added kernel_count & user_count for statistical unaligned access.
>
> If the NIC drivers requires this it is buggy.
Yes, you are right, but I've no control on their non-upstreamed
drivers. Every time kernel version updated I need to take care of that
issue for them. So just give them a back door in arch/csky and they
could disable it by manual.

> Kernel code must
> use the get_unaligned* / put_unaligned* helpers for that.
Most of ethernet drivers use netdev_alloc_skb_ip_align() to let
hardware deal with unaligned access,
but some NICs couldn't and we may modify kernel's skb_ip_header
parsing code with get_unaligned*/put_unaligned* ?

--
Best Regards
Guo Ren

ML: https://lore.kernel.org/linux-csky/

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