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

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Message-ID:
 <PAXPR04MB851043CBB0B4458BACE0AEBE88312@PAXPR04MB8510.eurprd04.prod.outlook.com>
Date: Fri, 6 Dec 2024 12:38:49 +0000
From: Wei Fang <wei.fang@....com>
To: Simon Horman <horms@...nel.org>
CC: Claudiu Manoil <claudiu.manoil@....com>, Vladimir Oltean
	<vladimir.oltean@....com>, Clark Wang <xiaoning.wang@....com>,
	"andrew+netdev@...n.ch" <andrew+netdev@...n.ch>, "davem@...emloft.net"
	<davem@...emloft.net>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	Frank Li <frank.li@....com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "imx@...ts.linux.dev" <imx@...ts.linux.dev>
Subject: RE: [PATCH v6 RESEND net-next 2/5] net: enetc: add Tx checksum
 offload for i.MX95 ENETC

> -----Original Message-----
> From: Simon Horman <horms@...nel.org>
> Sent: 2024年12月6日 20:32
> To: Wei Fang <wei.fang@....com>
> Cc: Claudiu Manoil <claudiu.manoil@....com>; Vladimir Oltean
> <vladimir.oltean@....com>; Clark Wang <xiaoning.wang@....com>;
> andrew+netdev@...n.ch; davem@...emloft.net; edumazet@...gle.com;
> kuba@...nel.org; pabeni@...hat.com; Frank Li <frank.li@....com>;
> netdev@...r.kernel.org; linux-kernel@...r.kernel.org; imx@...ts.linux.dev
> Subject: Re: [PATCH v6 RESEND net-next 2/5] net: enetc: add Tx checksum
> offload for i.MX95 ENETC
> 
> On Fri, Dec 06, 2024 at 10:46:49AM +0000, Wei Fang wrote:
> > > -----Original Message-----
> > > From: Simon Horman <horms@...nel.org>
> > > Sent: 2024年12月6日 17:37
> > > To: Wei Fang <wei.fang@....com>
> > > Cc: Claudiu Manoil <claudiu.manoil@....com>; Vladimir Oltean
> > > <vladimir.oltean@....com>; Clark Wang <xiaoning.wang@....com>;
> > > andrew+netdev@...n.ch; davem@...emloft.net; edumazet@...gle.com;
> > > kuba@...nel.org; pabeni@...hat.com; Frank Li <frank.li@....com>;
> > > netdev@...r.kernel.org; linux-kernel@...r.kernel.org;
> > > imx@...ts.linux.dev
> > > 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 <wei.fang@....com>
> > > > Reviewed-by: Frank Li <Frank.Li@....com>
> > > > Reviewed-by: Claudiu Manoil <claudiu.manoil@....com>
> > >
> > > ...
> > >
> > > > 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.
> 

I think I will use u8 instead of 32-bit, because I don't want to affect
the existing 'u8 flag'. And u8 is good enough.

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