linux-kernel - Re: [PATCH 14/15] net: phy: add PHY regulator support

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Date:   Tue, 23 Jun 2020 10:56:46 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>, Andrew Lunn <andrew@...n.ch>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        devicetree <devicetree@...r.kernel.org>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Fabien Parent <fparent@...libre.com>,
        Iyappan Subramanian <iyappan@...amperecomputing.com>,
        Quan Nguyen <quan@...amperecomputing.com>,
        Frank Rowand <frowand.list@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Andrew Perepech <andrew.perepech@...iatek.com>,
        Stephane Le Provost <stephane.leprovost@...iatek.com>,
        Keyur Chudgar <keyur@...amperecomputing.com>,
        Jassi Brar <jaswinder.singh@...aro.org>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Mark Brown <broonie@...nel.org>,
        "moderated list:ARM/Mediatek SoC..." 
        <linux-mediatek@...ts.infradead.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        netdev <netdev@...r.kernel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Pedro Tsai <pedro.tsai@...iatek.com>,
        "David S . Miller" <davem@...emloft.net>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH 14/15] net: phy: add PHY regulator support

On Tue, Jun 23, 2020 at 11:46:15AM +0200, Bartosz Golaszewski wrote:
> wt., 23 cze 2020 o 11:43 Russell King - ARM Linux admin
> <linux@...linux.org.uk> napisał(a):
> >
> > On Tue, Jun 23, 2020 at 11:41:11AM +0200, Bartosz Golaszewski wrote:
> > > pon., 22 cze 2020 o 15:29 Russell King - ARM Linux admin
> > > <linux@...linux.org.uk> napisał(a):
> > > >
> > >
> > > [snip!]
> > >
> > > >
> > > > This is likely to cause issues for some PHY drivers.  Note that we have
> > > > some PHY drivers which register a temperature sensor in the probe
> > > > function, which means they can be accessed independently of the lifetime
> > > > of the PHY bound to the network driver (which may only be while the
> > > > network device is "up".)  We certainly do not want hwmon failing just
> > > > because the network device is down.
> > > >
> > > > That's kind of worked around for the reset stuff, because there are two
> > > > layers to that: the mdio device layer reset support which knows nothing
> > > > of the PHY binding state to the network driver, and the phylib reset
> > > > support, but it is not nice.
> > > >
> > >
> > > Regulators are reference counted so if the hwmon driver enables it
> > > using mdio_device_power_on() it will stay on even after the PHY driver
> > > calls phy_device_power_off(), right? Am I missing something?
> >
> > If that is true, you will need to audit the PHY drivers to add that.
> >
> 
> This change doesn't have any effect on devices which don't have a
> regulator assigned in DT though. The one I'm adding in the last patch
> is the first to use this.

It's quality of implementation.

Should we wait for someone else to make use of the new regulator
support that has been added with a PHY that uses hwmon, and they
don't realise that it breaks hwmon on it, and several kernel versions
go by without it being noticed.  It will only be a noticable issue
when the associated network device is down, and that network device
driver detaches from the PHY, so _is_ likely not to be noticed.

Or should we do a small amount of work now to properly implement
regulator support, which includes a trivial grep for "hwmon" amongst
the PHY drivers, and add the necessary call to avoid the regulator
being shut off.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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