netdev - Re: [PATCH net-next v2] net: ethernet: ti: am65-cpsw: VLAN-aware CPSW only if !DSA

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Message-ID: <5864db3fdb5fea960b76a87d11527becf355650b.camel@siemens.com>
Date: Fri, 10 Jan 2025 11:48:45 +0000
From: "Sverdlin, Alexander" <alexander.sverdlin@...mens.com>
To: "s-vadapalli@...com" <s-vadapalli@...com>
CC: "c-vankar@...com" <c-vankar@...com>, "andrew+netdev@...n.ch"
	<andrew+netdev@...n.ch>, "davem@...emloft.net" <davem@...emloft.net>,
	"jpanis@...libre.com" <jpanis@...libre.com>, "kuba@...nel.org"
	<kuba@...nel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"rogerq@...nel.org" <rogerq@...nel.org>, "pabeni@...hat.com"
	<pabeni@...hat.com>
Subject: Re: [PATCH net-next v2] net: ethernet: ti: am65-cpsw: VLAN-aware CPSW
 only if !DSA

Hi Siddharth!

On Fri, 2025-01-10 at 17:12 +0530, Siddharth Vadapalli wrote:
> On Fri, Jan 10, 2025 at 12:27:17PM +0100, A. Sverdlin wrote:
> > From: Alexander Sverdlin <alexander.sverdlin@...mens.com>
> > 
> > Only configure VLAN-aware CPSW mode if no port is used as DSA CPU port.
> > VLAN-aware mode interferes with some DSA tagging schemes and makes stacking
> > DSA switches downstream of CPSW impossible. Previous attempts to address
> > the issue linked below.
> > 
> > Link: https://lore.kernel.org/netdev/20240227082815.2073826-1-s-vadapalli@ti.com/
> > Link: https://lore.kernel.org/linux-arm-kernel/4699400.vD3TdgH1nR@localhost/
> > Co-developed-by: Siddharth Vadapalli <s-vadapalli@...com>
> 
> A Co-developed-by tag should be followed by a Signed-off-by tag of the
> same individual.

You are right, thanks!

> > Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...mens.com>
> > ---
> > Changelog:
> > v2: Thanks to Siddharth it does look much clearer now (conditionally clear
> >      AM65_CPSW_CTL_VLAN_AWARE instead of setting)
> > 
> >   drivers/net/ethernet/ti/am65-cpsw-nuss.c | 18 ++++++++++++++----
> >   1 file changed, 14 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.c b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> > index 5465bf872734..58c840fb7e7e 100644
> > --- a/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> > +++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> > @@ -32,6 +32,7 @@
> >   #include <linux/dma/ti-cppi5.h>
> >   #include <linux/dma/k3-udma-glue.h>
> >   #include <net/page_pool/helpers.h>
> > +#include <net/dsa.h>
> >   #include <net/switchdev.h>
> >   
> >   #include "cpsw_ale.h"
> > @@ -724,13 +725,22 @@ static int am65_cpsw_nuss_common_open(struct am65_cpsw_common *common)
> >   	u32 val, port_mask;
> >   	struct page *page;
> >   
> > +	/* Control register */
> > +	val = AM65_CPSW_CTL_P0_ENABLE | AM65_CPSW_CTL_P0_TX_CRC_REMOVE |
> > +	      AM65_CPSW_CTL_VLAN_AWARE | AM65_CPSW_CTL_P0_RX_PAD;
> > +	/* VLAN aware CPSW mode is incompatible with some DSA tagging schemes.
> > +	 * Therefore disable VLAN_AWARE mode if any of the ports is a DSA Port.
> > +	 */
> > +	for (port_idx = 0; port_idx < common->port_num; port_idx++)
> > +		if (netdev_uses_dsa(common->ports[port_idx].ndev)) {
> > +			val &= ~AM65_CPSW_CTL_VLAN_AWARE;
> > +			break;
> > +		}
> > +	writel(val, common->cpsw_base + AM65_CPSW_REG_CTL);
> > +
> >   	if (common->usage_count)
> >   		return 0;
> 
> The changes above should be present HERE, i.e. below the
> "common->usage_count" check, as was the case earlier.

It has been moved deliberately, consider first port is being brought up
and only then the second port is being brought up (as part of
dsa_conduit_setup(), which sets dev->dsa_ptr right before opening the
port). As this isn't RMW operation and actually happens under RTNL lock,
moving in front of "if" looks safe to me... What do you think?

> > -	/* Control register */
> > -	writel(AM65_CPSW_CTL_P0_ENABLE | AM65_CPSW_CTL_P0_TX_CRC_REMOVE |
> > -	       AM65_CPSW_CTL_VLAN_AWARE | AM65_CPSW_CTL_P0_RX_PAD,
> > -	       common->cpsw_base + AM65_CPSW_REG_CTL);
> >   	/* Max length register */
> >   	writel(AM65_CPSW_MAX_PACKET_SIZE,
> >   	       host_p->port_base + AM65_CPSW_PORT_REG_RX_MAXLEN);

-- 
Alexander Sverdlin
Siemens AG
www.siemens.com