netdev - Re: [PATCH] net: dsa: mv88e6xxx: force cmode write on 6141/6341

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Message-ID: <20191221165153.GC2574713@t480s.localdomain>
Date:   Sat, 21 Dec 2019 16:51:53 -0500
From:   Vivien Didelot <vivien.didelot@...il.com>
To:     Baruch Siach <baruch@...s.co.il>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Marek Behún <marek.behun@....cz>,
        netdev@...r.kernel.org, Baruch Siach <baruch@...s.co.il>,
        Denis Odintsov <d.odintsov@...viangames.com>
Subject: Re: [PATCH] net: dsa: mv88e6xxx: force cmode write on 6141/6341

Hi Andrew,

On Fri, 20 Dec 2019 14:27:25 -0500, Vivien Didelot <vivien.didelot@...il.com> wrote:
> > mv88e6xxx_port_set_cmode() relies on cmode stored in struct
> > mv88e6xxx_port to skip cmode update when the requested value matches the
> > cached value. It turns out that mv88e6xxx_port_hidden_write() might
> > change the port cmode setting as a side effect, so we can't rely on the
> > cached value to determine that cmode update in not necessary.
> > 
> > Force cmode update in mv88e6341_port_set_cmode(), to make
> > serdes configuration work again. Other mv88e6xxx_port_set_cmode()
> > callers keep the current behaviour.
> > 
> > This fixes serdes configuration of the 6141 switch on SolidRun Clearfog
> > GT-8K.
> > 
> > Fixes: 7a3007d22e8 ("net: dsa: mv88e6xxx: fully support SERDES on Topaz family")
> > Reported-by: Denis Odintsov <d.odintsov@...viangames.com>
> > Signed-off-by: Baruch Siach <baruch@...s.co.il>
> 
> We tend to avoid caching values in the mv88e6xxx driver the more we can and
> query the hardware instead to avoid errors like this. We can consider calling a
> new mv88e6xxx_port_get_cmode() helper when needed (e.g. in higher level callers
> like mv88e6xxx_serdes_power() and mv88e6xxx_serdes_irq_thread_fn()) and pass
> the value down to the routines previously accessing chip->ports[port].cmode,
> as a new argument. I can prepare a patch doing this. What do you think?

I did not mention it, but mv88e6390x_serdes_get_lane() would access
mv88e6xxx_port_get_cmode(chip, 9) and mv88e6xxx_port_get_cmode(chip, 10)
internally since its implementation is specific.


Thanks,

	Vivien