Subject: Re: [PATCH 3/5] net: dsa: ksz: Factor out common tag code

From: Andrew Lunn <[email-masked]>
Date: Sat, 8 Dec 2018 12:34:48 +0100

On Fri, Dec 07, 2018 at 07:18:43PM +0100, Marek Vasut wrote:
> From: Tristram Ha <[email-masked]>
> 
> Factor out common code from the tag_ksz , so that the code can be used
> with other KSZ family switches which use differenly sized tags.

I prefer this implementation over what Tristram recently submitted. It
is also what we suggested a while back. However, since then we have
had Spectra/meltdown, and we now know a function call through a
pointer is expensive. This is the hot path, every frame comes through
here, so it is worth taking the time to optimize this. Could you try
to remove the ksz_tag_ops structure. xmit looks simple, since it is a
tail call, so you can do that in ksz9477_xmit. Receive looks a bit
more complex.

I also think for the moment we need it ignore PTP until we have the
big picture sorted out. If need be, the code can be refactored yet
again. But i don't want PTP holding up getting more switches
supported.

> Signed-off-by: Tristram Ha <[email-masked]>
> Signed-off-by: Marek Vasut <[email-masked]>
> Cc: Vivien Didelot <[email-masked]>
> Cc: Woojung Huh <[email-masked]>
> Cc: David S. Miller <[email-masked]>
> ---
>  net/dsa/tag_ksz.c | 125 +++++++++++++++++++++++++++++++++-------------
>  1 file changed, 90 insertions(+), 35 deletions(-)
> 
> diff --git a/net/dsa/tag_ksz.c b/net/dsa/tag_ksz.c
> index 036bc62198f28..d94bad1ab7e53 100644
> --- a/net/dsa/tag_ksz.c
> +++ b/net/dsa/tag_ksz.c
> @@ -14,34 +14,30 @@
>  #include <net/dsa.h>
>  #include "dsa_priv.h"
>  
> -/* For Ingress (Host -> KSZ), 2 bytes are added before FCS.
> - * ---------------------------------------------------------------------------
> - * DA(6bytes)|SA(6bytes)|....|Data(nbytes)|tag0(1byte)|tag1(1byte)|FCS(4bytes)
> - * ---------------------------------------------------------------------------
> - * tag0 : Prioritization (not used now)
> - * tag1 : each bit represents port (eg, 0x01=port1, 0x02=port2, 0x10=port5)
> - *
> - * For Egress (KSZ -> Host), 1 byte is added before FCS.
> - * ---------------------------------------------------------------------------
> - * DA(6bytes)|SA(6bytes)|....|Data(nbytes)|tag0(1byte)|FCS(4bytes)
> - * ---------------------------------------------------------------------------
> - * tag0 : zero-based value represents port
> - *	  (eg, 0x00=port1, 0x02=port3, 0x06=port7)
> - */
> +struct ksz_tag_ops {
> +	void	(*get_tag)(u8 *tag, unsigned int *port, unsigned int *len);
> +	void	(*set_tag)(struct sk_buff *skb, struct net_device *dev);
> +};
>  
> -#define	KSZ_INGRESS_TAG_LEN	2
> -#define	KSZ_EGRESS_TAG_LEN	1
> +/* Typically only one byte is used for tail tag. */
> +#define KSZ_EGRESS_TAG_LEN		1
>  
> -static struct sk_buff *ksz_xmit(struct sk_buff *skb, struct net_device *dev)
> +/* Frames with following addresse may need to be sent even when the port is
> + * closed.
> + */
> +static const u8 special_mult_addr[] = {
> +	0x01, 0x80, 0xC2, 0x00, 0x00, 0x00
> +};
> +

This is new functionality, not part of the refactoring the
code. Please add that as a new patch. Also, you can probably make use
of is_link_local_ether_addr().

   Andrew