netdev - Re: mt7530: dsa_switch_parse_of() fails, causes probe code to run twice

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Date:   Sun, 16 Apr 2023 12:57:10 +0100
From:   Daniel Golle <daniel@...rotopia.org>
To:     Arınç ÜNAL <arinc.unal@...nc9.com>
Cc:     Vladimir Oltean <olteanv@...il.com>,
        Frank Wunderlich <frank-w@...lic-files.de>,
        netdev <netdev@...r.kernel.org>, erkin.bozoglu@...ont.com,
        Thibaut <hacks@...shdirt.org>
Subject: Re: mt7530: dsa_switch_parse_of() fails, causes probe code to run
 twice

On Sun, Apr 16, 2023 at 12:38:03PM +0300, Arınç ÜNAL wrote:
> On 15.04.2023 17:57, Arınç ÜNAL wrote:
> > On 15.04.2023 17:20, Vladimir Oltean wrote:
> > > On Sat, Apr 15, 2023 at 03:02:10PM +0100, Daniel Golle wrote:
> > > > As the PHYs are accessed over the MDIO bus which is exposed by
> > > > the mt7530.c
> > > > DSA driver the only middle ground would possibly be to introduce a MFD
> > > > driver taking care of creating the bus access regmap (MDIO vs. MDIO) and
> > > > expose the mt7530-controlled MDIO bus.
> > > 
> > > Which is something I had already mentioned as a possible way forward in
> > > the other thread. One would need to take care of ensuring a reasonable
> > > migration path in terms of device tree compatibility though.
> > > 
> > > > 
> > > > Obviously that'd be a bit more work than just moving some things
> > > > from the
> > > > switch setup function to the probe function...
> > > 
> > > On the other hand, it would actually work reliably, and would not depend
> > > on whomever wanted to reorder things just a little bit differently for
> > > his system to probe faster.
> > 
> > Ok thanks. I will investigate how the switch would be set up with an MFD
> > driver, and how it would affect dt-bindings.
> > 
> > Looking back at my patch series, currently with this [0], SGMII on
> > MT7531BE's port 6 starts working, and with Daniel's addition [1], the
> > regulator warnings disappear.
> > 
> > I will submit the patch series as an RFC after addressing Daniel's
> > inline functions suggestion.
> 
> I've been giving this some thought. My understanding of probe in this
> context has changed drastically. The probe here is supposed to probe the
> driver, like setting up the pointers, reading from the devicetree, filling
> up the info table, and finally calling dsa_register_switch(). It would not
> necessarily do anything to the switch hardware like resetting and reading
> information from the registers. This is currently how mt7530-mdio and
> mt7530-mmio already operate. So I'm not going to move anything from setup to
> probe.
> 
> The duplicate code on mt7530_setup() and mt7531_setup() could rather be put
> on mt753x_setup() instead. But now there's ID_MT7988 also going through
> mt753x_setup, so it's not very feasible to do this anymore, too many ID
> checks there would be.
> 
> Moving forward, I will send a separate bugfix patch that makes port 6 on
> MT7531BE work. My patch series will solely be for improving the driver.
> 
> Daniel, can you confirm this patch is enough to make port 6 work on
> MT7531BE? I won't touch the PCS creation code here as it'd be an improvement
> rather than a fix, if this works.
> 
> https://github.com/arinc9/linux/commit/bb55b97b8f600cf28433e7ff494d296a15191cb3

Why don't we use my original solution [1] which has some advantages:

 * It doesn't requrire additional export of mt7530_regmap_bus

 * It doesn't move PCS creation to mt7530.c, hence PCS_MTK_LYNXI is
   only required for MDIO-connected switches
   (with your patch we would have to move the dependency on PCS_MTK_LYNXI
   from NET_DSA_MT7530_MDIO to NET_DSA_MT7530)

 * It doesn't expose the dysfunctional SerDes PCS for port 5 on MT7531BE
   This will still fail and hence result in probing on MT7531 to exit
   prematurely, preventing the switch driver from being loaded.
   Before 9ecc00164dc23 ("net: dsa: mt7530: refactor SGMII PCS creation")
   the return value of mtk_pcs_lynxi_create was ignored, now it isn't...

 * It changes much less in terms of LoC


I've of course also already addressed the comments of Jesse Brandeburg
and will submit it in a few moments.


[1]: https://patchwork.kernel.org/project/linux-mediatek/patch/ZDSlm-0gyyDZXy_k@makrotopia.org/

Thank you anyway for eyes and brains on this, I appreciate that.