netdev - Re: [net-next PATCH 05/19] net: dsa: qca8k: move read switch id function in qca8k

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Message-ID: <20211121183413.zjxs6yqbxq3a3a5h@skbuf>
Date:   Sun, 21 Nov 2021 20:34:13 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Ansuel Smith <ansuelsmth@...il.com>
Cc:     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>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [net-next PATCH 05/19] net: dsa: qca8k: move read switch id
 function in qca8k_setup

On Fri, Nov 19, 2021 at 02:08:59AM +0100, Ansuel Smith wrote:
> On Fri, Nov 19, 2021 at 03:03:05AM +0200, Vladimir Oltean wrote:
> > On Wed, Nov 17, 2021 at 10:04:37PM +0100, Ansuel Smith wrote:
> > > Move read_switch_id function in qca8k_setup in preparation for regmap
> > > conversion. Sw probe should NOT contain function that depends on reading
> > > from switch regs.
> > 
> > It shouldn't? Why? We have plenty of switch drivers that use regmap in
> > the probe function.
> >
> 
> The initial idea was to make a shared probe function. (when the ipq40xx
> code will be proposed)
> Currently the regmap is init in the setup function so we can both 
> move the switch id to setup or move regmap to probe.
> What should be better in your opinion?

Either one is fine, but it seems a bit backwards to call
dsa_register_switch() only to find out later, during the ->setup()
callback, that you're in fact talking to a potato. So from that point of
view maybe you could keep the device id check in ->probe, and therefore
also move the regmap initialization there.