# Re: \[PATCH v4 05/10\] net/fec: add dual fec support for mx28

- From: Lothar Waßmann \<hidden\>
- Date: 2011-01-17 08:16:22 
- List: netdev
- Page: https://ratatoskr.run/netdev/2011/01/8566068
- Thread: https://ratatoskr.run/linux-arm-kernel/2011/01/8565299/t.md

```text
Hi,

Shawn Guo writes:
> On Fri, Jan 14, 2011 at 08:52:23AM +0100, Uwe Kleine-König wrote:
> > On Fri, Jan 14, 2011 at 01:48:40PM +0800, Shawn Guo wrote:
> > > Hi Uwe,
> > > 
> > > On Thu, Jan 13, 2011 at 03:48:05PM +0100, Uwe Kleine-König wrote:
> > > 
> > > [...]
> > > 
> > > > > +/* Controller is ENET-MAC */
> > > > > +#define FEC_QUIRK_ENET_MAC           (1 << 0)
> > > > does this really qualify to be a quirk?
> > > > 
> > > My understanding is that ENET-MAC is a type of "quirky" FEC
> > > controller.
> > > 
> > > > > +/* Controller needs driver to swap frame */
> > > > > +#define FEC_QUIRK_SWAP_FRAME         (1 << 1)
> > > > IMHO this is a bit misnamed.  FEC_QUIRK_NEEDS_BE_DATA or similar would
> > > > be more accurate.
> > > > 
> > > When your make this change, you may want to pick a better name for
> > > function swap_buffer too.
> > > 
> > > [...]
> > > 
> > > > > +static void *swap_buffer(void *bufaddr, int len)
> > > > > +{
> > > > > +     int i;
> > > > > +     unsigned int *buf = bufaddr;
> > > > > +
> > > > > +     for (i = 0; i < (len + 3) / 4; i++, buf++)
> > > > > +             *buf = cpu_to_be32(*buf);
> > > > if len isn't a multiple of 4 this accesses bytes behind len.  Is this
> > > > generally OK here?  (E.g. because skbs always have a length that is a
> > > > multiple of 4?)
> > > The len may not be a multiple of 4.  But I believe bufaddr is always
> > > a buffer allocated in a length that is a multiple of 4, and the 1~3
> > > bytes exceeding the len very likely has no data that matters.  But
> > > yes, it deserves a safer implementation.
> > Did you test what happens if bufaddr isn't aligned?  Does it work at all
> > then?
> > 
> I see many calls passing a len that is not a multiple of 4, but it
> works good.
> 
That does not prove anything, actually.

Anyway "bufaddr isn't aligned" != "len is not a multiple of 4".
Is there any guarantee that the function cannot be called with a
non-aligned buffer address?


Lothar Waßmann
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