netdev - Re: [RFC PATCH v2 linux-next 13/14] net: dsa: sja1105: expose the SGMII PCS as an mdio

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Message-ID: <20210526154641.GJ30436@shell.armlinux.org.uk>
Date:   Wed, 26 May 2021 16:46:41 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [RFC PATCH v2 linux-next 13/14] net: dsa: sja1105: expose the
 SGMII PCS as an mdio_device

On Wed, May 26, 2021 at 06:41:02PM +0300, Vladimir Oltean wrote:
> On Wed, May 26, 2021 at 04:29:11PM +0100, Russell King (Oracle) wrote:
> > On Wed, May 26, 2021 at 04:55:34PM +0300, Vladimir Oltean wrote:
> > > Since we touch all PCS accessors again, now it is a good time to check
> > > for error codes from the hardware access as well. We can't propagate the
> > > errors very far due to phylink returning void for mac_config and
> > > mac_link_up, but at least we print them to the console.
> > 
> > phylink doesn't have much option on what it could do if we error out at
> > those points - I suppose we could print a non-specific error and then
> > lock-out the interface in a similar way that phylib does, but to me that
> > seems really unfriendly if you're remotely accessing a box and the error
> > is intermittent.
> 
> I would like to have intermittent errors at this level logged, because
> to me they would be quite unexpected and I would like to have some rope
> to pull while debugging - an error code, something.
> 
> If there's an error of any sort, the interface won't be fully
> initialized anyway, so not functional.
> 
> The reason why I added error checking in this patch is because I was
> working on the MDIO bus accessors and I wanted to make sure that the
> errors returned there are propagated somewhere.

Yes, makes sense there, but doesn't make sense if one is using the MMIO
accessors and have no errors to check...

My argument is - if you print an error at the lower levels, you can be
more specific about what failed. If you do it in phylink, you can only
say "oh, the blah_config() call failed" - which isn't particularly
useful.

Yes, we do this for some of the newly introduced methods, e.g. the
pcs_config() method - and there all we can say is:

                if (err < 0)
                        phylink_err(pl, "pcs_config failed: %pe\n",
                                    ERR_PTR(err));

-- 
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