netdev - Re: [PATCH 4/6] net/wan/fsl_ucc

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Date:   Wed, 29 Aug 2018 07:28:34 +0000
From:   Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
To:     "christophe.leroy@....fr" <christophe.leroy@....fr>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "qiang.zhao@....com" <qiang.zhao@....com>,
        David Gounaris <David.Gounaris@...inera.com>
Subject: Re: [PATCH 4/6] net/wan/fsl_ucc_hdlc: default hmask value

On Wed, 2018-08-29 at 09:18 +0200, Christophe LEROY wrote:
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.
> 
> 
> Le 29/08/2018 à 04:54, Qiang Zhao a écrit :
> > From: David Gounaris <david.gounaris@...inera.com>
> > Date: 2018/8/28 19:09
> > > Subject: [PATCH 4/6] net/wan/fsl_ucc_hdlc: default hmask value
> > > 
> > > Set default HMASK to 0x0000 to use
> > > promiscuous mode in the hdlc controller.
> 
> Why do you need to do that ?
> 
> An HDLC frame encapsulating Ethernet should look like:
> 
> HDLC Frame includes:
> – Opening Flag          7E hex
> – Address field         FF hex
> – Control field         03 hex
> – Information field     Original Ethernet Packet, 1522 octets max.
> – FCS CRC16             (2 bytes)
> – Closing Flag          7E hex

In our case the Eth frame starts directly after the Opening Flag so
there is no FF address field.

> 
> What do you mean by 'promiscuous mode' ?

Just that we don't want any address filtering of packets. I don't think this would
be a problem for pure HDLC frames either, do you?

> 
> In any case, should a filter mask be changed for promiscuous mode, I
> believe the change should be done at the time you enter promiscuous
> mode, not at all time.
> 
> Christophe
> 
> > > 
> > > Signed-off-by: David Gounaris <david.gounaris@...inera.com>
> > > ---
> > >   drivers/net/wan/fsl_ucc_hdlc.h | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/net/wan/fsl_ucc_hdlc.h b/drivers/net/wan/fsl_ucc_hdlc.h
> > > index c21134c1f180..5bc3d1a6ca6e 100644
> > > --- a/drivers/net/wan/fsl_ucc_hdlc.h
> > > +++ b/drivers/net/wan/fsl_ucc_hdlc.h
> > > @@ -134,7 +134,7 @@ struct ucc_hdlc_private {
> > > 
> > >   #define HDLC_HEAD_MASK             0x0000
> > >   #define DEFAULT_HDLC_HEAD  0xff44
> > > -#define DEFAULT_ADDR_MASK   0x00ff
> > > +#define DEFAULT_ADDR_MASK   0x0000
> > >   #define DEFAULT_HDLC_ADDR  0x00ff
> > > 
> > >   #define BMR_GBL                    0x20000000
> > > --
> > 
> > It is not proper to set default HMASK to 0x0000, how about to add a new property standing for hmask into device tree,
> > If get this property from dtb, then set it with the value from dtb, otherwise, set it with default HMASK ox00ff?
> > 
> > Best Regards
> > Qiang Zhao
> >