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From:   DENG Qingfang <dqfext@gmail.com>
To:     Alvin =?utf-8?Q?=C5=A0ipraga?= <ALSI@bang-olufsen.dk>
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        Linus Walleij <linus.walleij@linaro.org>,
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        Jakub Kicinski <kuba@kernel.org>,
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Subject: Re: [PATCH net-next 5/6] net: dsa: realtek-smi: add rtl8365mb subdriver for RTL8365MB-VC
Date:   Wed, 13 Oct 2021 18:13:41 +0800
Message-Id: <20211013101341.56223-1-dqfext@gmail.com>
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References: <20211012123557.3547280-1-alvin@pqrs.dk> <20211012123557.3547280-6-alvin@pqrs.dk> <20211013095505.55966-1-dqfext@gmail.com> <32ffccb4-ff8b-5e60-ad29-e32bcb22969f@bang-olufsen.dk>
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On Wed, Oct 13, 2021 at 10:05:21AM +0000, Alvin Šipraga wrote:
> 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)?

So set num_ports to 7.

> 
> > 
> >> +
> >> +/* Chip-specific data and limits */
>