[PATCH] ucc_geth: Add 8 bytes to max TX frame for VLANs
LeoLi at freescale.com
Fri Mar 28 13:54:16 EST 2008
> > Hi Jocke,
> > QUICC engine supports dynamic maximum frame length. If you are not
> > expecting to receive only tagged frames, I recommend to use this
> > feature by setting dynamicMaxFrameLength and
> dynamicMinFrameLength in
> > ug_info instead of increasing the MaxLength for both tagged
> and untagged frames.
> > See the following part from the reference manual.
> > The MFLR entry in the Global Parameter RAM defines the
> length of the
> > largest frame, excluding Q TAG but including FCS, that is
> still valid.
> > When REMODER[DXE]=1, a tagged frame that has length equals
> > MaxLength+4 considered valid, and a non tagged frame that has length
> > equals MaxLength is the longest
> > that is still considered valid. When REMODER[DXE]=0, any
> frame longer
> > than MaxLength consider erroneous frame.
> > For systems with only tagged frames, set REMODER[DXE]=0 and set
> > MaxLength = Max LLC size+4.
> > - Leo
> Interesting, that should also work although QinQ will not. I
> will have a closer look but I still don't see how my orginal
> patch would harm anything. One could add my patch on top but
> with only 4 bytes extra.
The increase of max packet length may cause a waste of QE internal
buffer for every packet. Furthermore it affects the hardware statistics
of jumbo packets.
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