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Re: kern/46961: Please support BCM57762 Ethernet arapter(Apple'sThunderbolt Ethernet Adapter)
The following reply was made to PR kern/46961; it has been noted by GNATS.
From: David Laight <david%l8s.co.uk@localhost>
Subject: Re: kern/46961: Please support BCM57762 Ethernet
arapter(Apple'sThunderbolt Ethernet Adapter)
Date: Mon, 17 Sep 2012 07:57:39 +0100
On Mon, Sep 17, 2012 at 04:45:02AM +0000, Izumi Tsutsui wrote:
> The following reply was made to PR kern/46961; it has been noted by GNATS.
> From: Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>
> To: ryo_on%yk.rim.or.jp@localhost
> Cc: gnats-bugs%NetBSD.org@localhost, tsutsui%ceres.dti.ne.jp@localhost
> Subject: Re: kern/46961: Please support BCM57762 Ethernet
> Ethernet Adapter)
> Date: Mon, 17 Sep 2012 13:41:25 +0900
> > http://www.netbsd.org/~ryoon/120916b-bcm57762.diff
> > I have defined ETHER_VLAN_MAX_LEN in the suggested place of if_bgereg.h.
> > It works.
> I notice original FreeBSD's bge driver uses BGE_MAX_FRAMELEN for
> BGE_RX_STD_RCB_MAXLEN_FLAGS register, and we also use it in
> older !BGE_IS_5705_PLUS(sc) case.
> The value is used to specify "Maximum Ethernet Frame Length"
> for RX descriptors, so 1536 bytes should also work and using it
> as a bge's magic number would be better to avoid divergence
> from other OSes.
> In our if_bgereg.h, BGE_MAX_FRAMELEN is defined as following:
> > #define BGE_MAX_FRAMELEN (ETHER_MAX_LEN + ETHER_HDR_LEN + ETHER_CRC_LEN)
> but this seems wrong because ETHER_MAX_LEN already includes header
> and CRC length, and the original FreeBSD's bge just defines it as "1536"
> (though ETHER_MAX_LEN + ETHER_HDR_LEN + ETHER_CRC_LEN is also 1536),
> so I'll change BGE_MAX_FRAMELEN definition.
There are all sorts of reasons why an rx buffer size of 1536 is a good idea.
Mostly because it is a nice round number!
It might even be that the register it gets written to has non-writeable
Allowing 'slightly overlong' packets is useful for certain protocols,
I'm sure I remember something else, as well as VLAN, extending the
Generating 1536 as in BGE_MAX_FRAMELEN above is rather bogus though.
I also don't really remember DIX meaning anything in particular.
David Laight: david%l8s.co.uk@localhost
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