Re: [PATCH 14/15] net: phy: add PHY regulator support - Russell King

From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Cc: Bartosz Golaszewski <brgl@bgdev.pl>, Andrew Lunn <andrew@lunn.ch>,
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	Heiner Kallweit <hkallweit1@gmail.com>
Subject: Re: [PATCH 14/15] net: phy: add PHY regulator support
Date: Tue, 23 Jun 2020 10:56:46 +0100	[thread overview]
Message-ID: <20200623095646.GT1551@shell.armlinux.org.uk> (raw)
In-Reply-To: <CAMpxmJVP9db-4-AA4e1JkEfrajvJ4s0T6zo5+oFzpJHRBcuSsg@mail.gmail.com>

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@armlinux.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@armlinux.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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