netdev - Re: [PATCH net-next v5 1/3] net: dsa: microchip: ksz8: Make flow control, speed, and duplex on CPU port configurable

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Date: Wed, 22 Nov 2023 10:45:54 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: "David S. Miller" <davem@...emloft.net>, Andrew Lunn <andrew@...n.ch>,
	Eric Dumazet <edumazet@...gle.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Vladimir Oltean <olteanv@...il.com>,
	Woojung Huh <woojung.huh@...rochip.com>,
	Arun Ramadoss <arun.ramadoss@...rochip.com>,
	Simon Horman <simon.horman@...igine.com>, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH net-next v5 1/3] net: dsa: microchip: ksz8: Make flow
 control, speed, and duplex on CPU port configurable

On Wed, Nov 22, 2023 at 09:38:09AM +0000, Russell King (Oracle) wrote:
> On Wed, Nov 22, 2023 at 10:25:43AM +0100, Oleksij Rempel wrote:
> > Allow flow control, speed, and duplex settings on the CPU port to be
> > configurable. Previously, the speed and duplex relied on default switch
> > values, which limited flexibility. Additionally, flow control was
> > hardcoded and only functional in duplex mode. This update enhances the
> > configurability of these parameters.
> > 
> > Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> > Reviewed-by: Simon Horman <simon.horman@...igine.com>
> > Reviewed-by: Vladimir Oltean <olteanv@...il.com>
> > ---
> >  drivers/net/dsa/microchip/ksz8.h       |  4 ++
> >  drivers/net/dsa/microchip/ksz8795.c    | 54 +++++++++++++++++++++++++-
> >  drivers/net/dsa/microchip/ksz_common.c |  1 +
> >  3 files changed, 57 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/dsa/microchip/ksz8.h b/drivers/net/dsa/microchip/ksz8.h
> > index ef653bbfde75..571c26ce71e4 100644
> > --- a/drivers/net/dsa/microchip/ksz8.h
> > +++ b/drivers/net/dsa/microchip/ksz8.h
> > @@ -54,5 +54,9 @@ int ksz8_reset_switch(struct ksz_device *dev);
> >  int ksz8_switch_init(struct ksz_device *dev);
> >  void ksz8_switch_exit(struct ksz_device *dev);
> >  int ksz8_change_mtu(struct ksz_device *dev, int port, int mtu);
> > +void ksz8_phylink_mac_link_up(struct ksz_device *dev, int port,
> > +			      unsigned int mode, phy_interface_t interface,
> > +			      struct phy_device *phydev, int speed, int duplex,
> > +			      bool tx_pause, bool rx_pause);
> >  
> >  #endif
> > diff --git a/drivers/net/dsa/microchip/ksz8795.c b/drivers/net/dsa/microchip/ksz8795.c
> > index 8deb217638d3..3504e7238eba 100644
> > --- a/drivers/net/dsa/microchip/ksz8795.c
> > +++ b/drivers/net/dsa/microchip/ksz8795.c
> > @@ -1528,6 +1528,58 @@ void ksz8_config_cpu_port(struct dsa_switch *ds)
> >  	}
> >  }
> >  
> > +/**
> > + * ksz8_cpu_port_link_up - Configures the CPU port of the switch.
> > + * @dev: The KSZ device instance.
> > + * @speed: The desired link speed.
> > + * @duplex: The desired duplex mode.
> > + * @tx_pause: If true, enables transmit pause.
> > + * @rx_pause: If true, enables receive pause.
> > + *
> > + * Description:
> > + * The function configures flow control and speed settings for the CPU
> > + * port of the switch based on the desired settings, current duplex mode, and
> > + * speed.
> > + */
> > +static void ksz8_cpu_port_link_up(struct ksz_device *dev, int speed, int duplex,
> > +				  bool tx_pause, bool rx_pause)
> > +{
> > +	const u16 *regs = dev->info->regs;
> > +	u8 ctrl = 0;
> > +
> > +	/* SW_FLOW_CTRL, SW_HALF_DUPLEX, and SW_10_MBIT bits are bootstrappable
> > +	 * at least on KSZ8873. They can have different values depending on your
> > +	 * board setup.
> > +	 */
> > +	if (duplex) {
> > +		if (tx_pause || rx_pause)
> > +			ctrl |= SW_FLOW_CTRL;
> 
> Please don't make this dependent on duplex, and allow phylink to enforce
> that. For example, phylink_resolve_an_pause() will only enable tx/rx
> pause if in full duplex mode.

OK, thx.

> > +	} else {
> > +		ctrl |= SW_HALF_DUPLEX;
> > +	}
> > +
> > +	/* This hardware only supports SPEED_10 and SPEED_100. For SPEED_10
> > +	 * we need to set the SW_10_MBIT bit. Otherwise, we can leave it 0.
> > +	 */
> > +	if (speed == SPEED_10)
> > +		ctrl |= SW_10_MBIT;
> > +
> > +	ksz_rmw8(dev, regs[S_BROADCAST_CTRL], SW_HALF_DUPLEX | SW_FLOW_CTRL |
> > +		 SW_10_MBIT, ctrl);
> 
> So this is using SW_FLOW_CTRL with the S_BROADCAST_CTRL register...
> 
> > @@ -1576,8 +1628,6 @@ int ksz8_setup(struct dsa_switch *ds)
> >  	 */
> >  	ds->vlan_filtering_is_global = true;
> >  
> > -	ksz_cfg(dev, S_REPLACE_VID_CTRL, SW_FLOW_CTRL, true);
> 
> But previously it was being used with the S_REPLACE_VID_CTRL register.
> Doesn't make sense to me.

Yes, it looks suspicious. There are multiple ways to access same
register. Vladimir pointed to in in the v4 review. S_BROADCAST_CTRL is
used in most recent code. So, i decided to settle down to the variant.

Regards,
Oleksij
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