netdev - Re: [PATCH net-next v3 3/3] net: dsa: rzn1-a5psw: add vlan support

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Message-ID: <20230209094725.3ac772ff@fixe.home>
Date:   Thu, 9 Feb 2023 09:47:25 +0100
From:   Clément Léger <clement.leger@...tlin.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Herve Codina <herve.codina@...tlin.com>,
        Miquèl Raynal <miquel.raynal@...tlin.com>,
        Milan Stevanovic <milan.stevanovic@...com>,
        Jimmy Lalande <jimmy.lalande@...com>,
        Pascal Eberhard <pascal.eberhard@...com>,
        Arun Ramadoss <Arun.Ramadoss@...rochip.com>,
        linux-renesas-soc@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 3/3] net: dsa: rzn1-a5psw: add vlan support

Le Thu, 9 Feb 2023 00:03:09 +0200,
Vladimir Oltean <olteanv@...il.com> a écrit :

> On Wed, Feb 08, 2023 at 05:17:49PM +0100, Clément Léger wrote:
> > +static void a5psw_port_vlan_tagged_cfg(struct a5psw *a5psw, int vlan_res_id,
> > +				       int port, bool set)
> > +{
> > +	u32 mask = A5PSW_VLAN_RES_WR_PORTMASK | A5PSW_VLAN_RES_RD_TAGMASK |
> > +		   BIT(port);
> > +	u32 vlan_res_off = A5PSW_VLAN_RES(vlan_res_id);
> > +	u32 val = A5PSW_VLAN_RES_WR_TAGMASK, reg;
> > +
> > +	if (set)
> > +		val |= BIT(port);
> > +
> > +	/* Toggle tag mask read */
> > +	a5psw_reg_writel(a5psw, vlan_res_off, A5PSW_VLAN_RES_RD_TAGMASK);
> > +	reg = a5psw_reg_readl(a5psw, vlan_res_off);
> > +	a5psw_reg_writel(a5psw, vlan_res_off, A5PSW_VLAN_RES_RD_TAGMASK);  
> 
> Is it intentional that this register is written twice?

Yes, the A5PSW_VLAN_RES_RD_TAGMASK bit is a toggle-bit (toggled
by writing a 1 in it) and it allows to read the tagmask (for
vlan tagging) instead of the portmask (for vlan membership):

"""
b28 read_tagmask:

Select contents of mask bits (4:0) when reading the
register. If this bit is set during a write into the register, all
other bits of the write are ignored (i.e. 30,29,16:0) and the bit 28 of
the register toggles (1-> 0; 0-> 1). This is used only to allow
changing the bit 28 without changing any table contents.
"""

> 
> > +
> > +	reg &= ~mask;
> > +	reg |= val;
> > +	a5psw_reg_writel(a5psw, vlan_res_off, reg);
> > +}  



-- 
Clément Léger,
Embedded Linux and Kernel engineer at Bootlin
https://bootlin.com