netdev - Re: [PATCH net-next 5/6] net: dsa: realtek-smi: add rtl8365mb subdriver for RTL8365MB-VC

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Message-ID: <20211013101046.ofmmyy2fuwjkkcia@skbuf>
Date:   Wed, 13 Oct 2021 13:10:46 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Alvin Šipraga <ALSI@...g-olufsen.dk>
Cc:     DENG Qingfang <dqfext@...il.com>,
        Alvin Šipraga <alvin@...s.dk>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Michael Rasmussen <MIR@...g-olufsen.dk>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 5/6] net: dsa: realtek-smi: add rtl8365mb
 subdriver for RTL8365MB-VC

On Wed, Oct 13, 2021 at 10:05:21AM +0000, Alvin Šipraga wrote:
> On 10/13/21 11:55 AM, DENG Qingfang wrote:
> > On Tue, Oct 12, 2021 at 02:35:54PM +0200, Alvin Šipraga wrote:
> >> +/* Port mapping macros
> >> + *
> >> + * PORT_NUM_x2y: map a port number from domain x to domain y
> >> + * PORT_MASK_x2y: map a port mask from domain x to domain y
> >> + *
> >> + * L = logical port domain, i.e. dsa_port.index
> >> + * P = physical port domain, used by the Realtek ASIC for port indexing;
> >> + *     for ports with internal PHYs, this is also the PHY index
> >> + * E = extension port domain, used by the Realtek ASIC for managing EXT ports
> >> + *
> >> + * The terminology is borrowed from the vendor driver. The extension port domain
> >> + * is mostly used to navigate the labyrinthine layout of EXT port configuration
> >> + * registers and is not considered intuitive by the author.
> >> + *
> >> + * Unless a function is accessing chip registers, it should be using the logical
> >> + * port domain. Moreover, function arguments for port numbers and port masks
> >> + * must always be in the logical domain. The conversion must be done as close as
> >> + * possible to the register access to avoid chaos.
> >> + *
> >> + * The mappings vary between chips in the family supported by this driver. Here
> >> + * is an example of the mapping for the RTL8365MB-VC:
> >> + *
> >> + *    L | P | E | remark
> >> + *   ---+---+---+--------
> >> + *    0 | 0 |   | user port
> >> + *    1 | 1 |   | user port
> >> + *    2 | 2 |   | user port
> >> + *    3 | 3 |   | user port
> >> + *    4 | 6 | 1 | extension (CPU) port
> >> + *
> >> + * NOTE: Currently this is hardcoded for the RTL8365MB-VC. This will probably
> >> + * require a rework when adding support for other chips.
> >> + */
> >> +#define CPU_PORT_LOGICAL_NUM	4
> >> +#define CPU_PORT_LOGICAL_MASK	BIT(CPU_PORT_LOGICAL_NUM)
> >> +#define CPU_PORT_PHYSICAL_NUM	6
> >> +#define CPU_PORT_PHYSICAL_MASK	BIT(CPU_PORT_PHYSICAL_NUM)
> >> +#define CPU_PORT_EXTENSION_NUM	1
> >> +
> >> +static u32 rtl8365mb_port_num_l2p(u32 port)
> >> +{
> >> +	return port == CPU_PORT_LOGICAL_NUM ? CPU_PORT_PHYSICAL_NUM : port;
> >> +}
> >> +
> >> +static u32 rtl8365mb_port_mask_l2p(u32 mask)
> >> +{
> >> +	u32 phys_mask = mask & ~CPU_PORT_LOGICAL_MASK;
> >> +
> >> +	if (mask & CPU_PORT_LOGICAL_MASK)
> >> +		phys_mask |= CPU_PORT_PHYSICAL_MASK;
> >> +
> >> +	return phys_mask;
> >> +}
> >> +
> >> +static u32 rtl8365mb_port_mask_p2l(u32 phys_mask)
> >> +{
> >> +	u32 mask = phys_mask & ~CPU_PORT_PHYSICAL_MASK;
> >> +
> >> +	if (phys_mask & CPU_PORT_PHYSICAL_MASK)
> >> +		mask |= CPU_PORT_LOGICAL_MASK;
> >> +
> >> +	return mask;
> >> +}
> >> +
> >> +#define PORT_NUM_L2P(_p) (rtl8365mb_port_num_l2p(_p))
> >> +#define PORT_NUM_L2E(_p) (CPU_PORT_EXTENSION_NUM)
> >> +#define PORT_MASK_L2P(_m) (rtl8365mb_port_mask_l2p(_m))
> >> +#define PORT_MASK_P2L(_m) (rtl8365mb_port_mask_p2l(_m))
> >
> > The whole port mapping thing can be avoided if you just use port 6 as the CPU
> > port.
>
> Andrew also suggested this, but the discontinuity in port IDs seems to
> be an invitation for trouble. Here is an example of a series of
> functions from dsa.h:
>
> static inline struct dsa_port *dsa_to_port(struct dsa_switch *ds, int p)
> {
> 	struct dsa_switch_tree *dst = ds->dst;
> 	struct dsa_port *dp;
>
> 	list_for_each_entry(dp, &dst->ports, list)
> 		if (dp->ds == ds && dp->index == p)
> 			return dp;
>
> 	return NULL;
> }
>
> static inline bool dsa_is_user_port(struct dsa_switch *ds, int p)
> {
> 	return dsa_to_port(ds, p)->type == DSA_PORT_TYPE_USER;
> }
>
> static inline u32 dsa_user_ports(struct dsa_switch *ds)
> {
> 	u32 mask = 0;
> 	int p;
>
> 	for (p = 0; p < ds->num_ports; p++)
> 		if (dsa_is_user_port(ds, p))
> 			mask |= BIT(p);
>
> 	return mask;
> }
>
> My reading of dsa_user_ports() is that the port IDs run from 0 to
> (ds->num_ports - 1). If num_ports is 5 (4 user ports and 1 CPU port, as
> in my case), but the CPU is port 6, will we not dereference NULL when
> calling dsa_is_user_port(ds, 4)?
>
> >
> >> +
> >> +/* Chip-specific data and limits */
>

No, have you actually tried it? Discontinuities should be absolutely
fine, see dsa_switch_touch_ports(), a struct dsa_port is created for
every port number up to ds->num_ports, the ones absent from DT will
simply remain as DSA_PORT_TYPE_UNUSED.