netdev - Re: [PATCH v2] net: add Fast Ethernet driver for PXA168.

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Date:	Tue, 10 Aug 2010 20:01:54 +0200
From:	Lennert Buytenhek <buytenh@...tstofly.org>
To:	Philip Rakity <prakity@...vell.com>
Cc:	Sachin Sanap <ssanap@...vell.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Ashish Karkare <akarkare@...vell.com>,
	Prabhanjan Sarnaik <sarnaik@...vell.com>,
	"eric.y.miao@...il.com" <eric.y.miao@...il.com>,
	Mark Brown <markb@...vell.com>
Subject: Re: [PATCH v2]  net: add Fast Ethernet driver for PXA168.

On Tue, Aug 10, 2010 at 10:55:02AM -0700, Philip Rakity wrote:

> We agree that extra header prepend space is needed.  The solution of
> globally defining SKB_NET_PAD to increase this area for all drivers
> is where I have some concern.  The solution certainly works but at
> the cost of extra space for drivers that do not need to do this.
> The solution is fine by me and maybe the best answer is to increase
> the value in the standard linux implementation from 32 to 48 or 64 bytes. 

What I said was:

| This seems like something that, should you want to handle it, should be
| handled centrally (e.g. by conditionally increasing NET_SKB_PAD or so)
| and not hardcoded into one specific driver only.

In other words, "don't hardcode it into your driver just because you
think that most users will want to use your driver for bridging/routing
to wlan".

It makes no sense to categorically declare that "pxa168_eth will always
be used for routing to wireless, so we'll add some extra headroom by
default there, but e1000e will not, so there we won't".

Even if this stays a private kernel tree hack, I would still do it
globally rather than locally.

> > > 11n needs more.
> > 
> > Really?  Pointer?

Still curious about this.
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