Re: [PATCH v1 1/2] driver core: fw_devlink: Add support for FWNODE_FLAG_BROKEN_PARENT

From: Saravana Kannan <saravanak@google.com>
To: Vladimir Oltean <olteanv@gmail.com>
Cc: Andrew Lunn <andrew@lunn.ch>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>, Len Brown <lenb@kernel.org>,
	Alvin Sipraga <ALSI@bang-olufsen.dk>,
	kernel-team@android.com, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org, linux-acpi@vger.kernel.org
Subject: Re: [PATCH v1 1/2] driver core: fw_devlink: Add support for FWNODE_FLAG_BROKEN_PARENT
Date: Wed, 29 Sep 2021 22:33:16 -0700	[thread overview]
Message-ID: <CAGETcx8MXzFhhxom3u2MXw8XA-uUtm9XGEbYNobfr+Ptq5+fVQ@mail.gmail.com> (raw)
In-Reply-To: <20210831231804.zozyenear45ljemd@skbuf>

On Tue, Aug 31, 2021 at 4:18 PM Vladimir Oltean <olteanv@gmail.com> wrote:
>
> On Wed, Sep 01, 2021 at 01:02:09AM +0200, Andrew Lunn wrote:
> > Rev B is interesting because switch0 and switch1 got genphy, while
> > switch2 got the correct Marvell PHY driver. switch2 PHYs don't have
> > interrupt properties, so don't loop back to their parent device.
>
> This is interesting and not what I really expected to happen. It goes to
> show that we really need more time to understand all the subtleties of
> device dependencies before jumping on patching stuff.
>
> In case the DSA tree contains more than one switch, different things
> will happen in dsa_register_switch().
> The tree itself is only initialized when the last switch calls
> dsa_register_switch(). All the other switches just mark themselves as
> present and exit probing early. See this piece of code in dsa_tree_setup:
>
>         complete = dsa_tree_setup_routing_table(dst);
>         if (!complete)
>                 return 0;

Hi Vladimir,

Can you point me to an example dts file that has a DSA tree with more
than one switch and also point me to the switches that form the tree?

I'm working on a RFC series that tries to improve some stuff and
having an example DTS to look at would help.

Thanks,
Saravana

>
> So it should be a general property of cross-chip DSA trees that all
> switches except the last one will have the specific PHY driver probed
> properly, and not the genphy.
>
> Because all (N - 1) switches of a tree exit early in dsa_register_switch,
> they have successfully probed by the time the last switch brings up the
> tree, and brings up the PHYs on behalf of every other switch.
>
> The last switch can connect to the PHY on behalf of the other switches
> past their probe ending, and those PHYs should not defer probing because
> their supplier is now probed. It is only that the last switch cannot
> connect to the PHYs of its own ports.
>
> So if this does not work (you say that there are 2 switches that use
> genphy) I suspect there are also other bugs involved.