Subject: Re: [PATCH v6 RESEND net-next 2/5] net: enetc: add Tx checksum offload for i.MX95 ENETC

From: Simon Horman <[email-masked]>
Date: Fri, 6 Dec 2024 12:32:19 +0000

On Fri, Dec 06, 2024 at 10:46:49AM +0000, Wei Fang wrote:
> > -----Original Message-----
> > From: Simon Horman <[email-masked]>
> > Sent: 2024年12月6日 17:37
> > To: Wei Fang <[email-masked]>
> > Cc: Claudiu Manoil <[email-masked]>; Vladimir Oltean
> > <[email-masked]>; Clark Wang <[email-masked]>;
> > [email-masked]; [email-masked]; [email-masked];
> > [email-masked]; [email-masked]; Frank Li <[email-masked]>;
> > [email-masked]; [email-masked]; [email-masked]
> > Subject: Re: [PATCH v6 RESEND net-next 2/5] net: enetc: add Tx checksum
> > offload for i.MX95 ENETC
> > 
> > On Wed, Dec 04, 2024 at 01:29:29PM +0800, Wei Fang wrote:
> > > In addition to supporting Rx checksum offload, i.MX95 ENETC also supports
> > > Tx checksum offload. The transmit checksum offload is implemented through
> > > the Tx BD. To support Tx checksum offload, software needs to fill some
> > > auxiliary information in Tx BD, such as IP version, IP header offset and
> > > size, whether L4 is UDP or TCP, etc.
> > >
> > > Same as Rx checksum offload, Tx checksum offload capability isn't defined
> > > in register, so tx_csum bit is added to struct enetc_drvdata to indicate
> > > whether the device supports Tx checksum offload.
> > >
> > > Signed-off-by: Wei Fang <[email-masked]>
> > > Reviewed-by: Frank Li <[email-masked]>
> > > Reviewed-by: Claudiu Manoil <[email-masked]>
> > 
> > ...
> > 
> > > diff --git a/drivers/net/ethernet/freescale/enetc/enetc_hw.h
> > b/drivers/net/ethernet/freescale/enetc/enetc_hw.h
> > > index 4b8fd1879005..590b1412fadf 100644
> > > --- a/drivers/net/ethernet/freescale/enetc/enetc_hw.h
> > > +++ b/drivers/net/ethernet/freescale/enetc/enetc_hw.h
> > > @@ -558,7 +558,12 @@ union enetc_tx_bd {
> > >  		__le16 frm_len;
> > >  		union {
> > >  			struct {
> > > -				u8 reserved[3];
> > > +				u8 l3_start:7;
> > > +				u8 ipcs:1;
> > > +				u8 l3_hdr_size:7;
> > > +				u8 l3t:1;
> > > +				u8 resv:5;
> > > +				u8 l4t:3;
> > >  				u8 flags;
> > >  			}; /* default layout */
> > 
> > Hi Wei,
> > 
> > Given that little-endian types are used elsewhere in this structure
> > I am guessing that the layout above works for little-endian hosts
> > but will not work on big-endian hosts.
> > 
> > If so, I would suggest an alternate approach of using a single 32-bit
> > word and accessing it using a combination of FIELD_PREP() and FIELD_GET()
> > using masks created using GENMASK() and BIT().
> 
> Good suggestion, I will refine it, thanks.

Thanks. I forgot to mention that you will likely also need to add
cpu_to_le32 and le32_to_cpu to the mix.

> > Or, less desirably IMHO, by providing an alternate layout for
> > the embedded struct for big endian systems.
> > 
> > ...
>