lkml.org 
[lkml]   [2012]   [Oct]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/2] staging: et131x: Fix 64bit tx dma address handling
On Thu, Oct 18, 2012 at 10:59:56AM +0100, Alan Cox wrote:
> > > + skb_headlen(skb),
> > > + DMA_TO_DEVICE);
> > > + desc[frag].addr_lo = dma_addr & 0xFFFFFFFF;
> > > + desc[frag].addr_hi = dma_addr >> 32;
> >
> > Maybe use macros defined in kernel.h instead:
> >
> > desc[frag].addr_lo = lower_32_bits(dma_addr);
> > desc[frag].addr_hi = upper_32_bits(dma_addr);
> >
> > A few more instances below.
>
> This is actually important because >> 32 of a 32bit value is undefined in
> C. The compiler is free to do what it likes with this. While the results
> are usually sane some architectures do generate the equivalent of
>
> x >> (n % wordsize);
>
> Alan

Thanks for the comments both. I'll send an updated patch this evening.

The intention is to eventually store this value as a dma_addr_t anyway,
but some more work needs to be done to copy the address correctly to the
desc ring.

Cheers,

Mark


\
 
 \ /
  Last update: 2012-10-18 13:01    [W:0.032 / U:0.228 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site