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Date:   Mon, 4 Oct 2021 09:04:38 +0200
From:   Marek =?UTF-8?B?QmVow7pu?= <kabel@kernel.org>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Andrew Lunn <andrew@lunn.ch>, Pavel Machek <pavel@ucw.cz>,
        "linux-leds@vger.kernel.org" <linux-leds@vger.kernel.org>,
        netdev@vger.kernel.org,
        Jacek Anaszewski <jacek.anaszewski@gmail.com>,
        linux-kernel@vger.kernel.org
Subject: Re: are device names part of sysfs ABI? (was Re: devicename part of
 LEDs under ethernet MAC / PHY)
Message-ID: <20211004090438.588a8a89@thinkpad>
In-Reply-To: <YVqhMeuDI0IZL/zY@kroah.com>
References: <20211001133057.5287f150@thinkpad>
        <YVb/HSLqcOM6drr1@lunn.ch>
        <20211001144053.3952474a@thinkpad>
        <20211003225338.76092ec3@thinkpad>
        <YVqhMeuDI0IZL/zY@kroah.com>
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Hi Greg,

On Mon, 4 Oct 2021 08:37:37 +0200
Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:

> On Sun, Oct 03, 2021 at 10:53:38PM +0200, Marek Beh=C3=BAn wrote:
> > Hello Greg,
> >=20
> > could you give your opinion on this discussion? =20
>=20
> What discussion?  Top posting ruins that :(

Sorry, the discussion is here
https://lore.kernel.org/linux-leds/20211001144053.3952474a@thinkpad/T/
But the basic question is below, so you don't need to read the
discussion.

> > Are device names (as returned by dev_name() function) also part of
> > sysfs ABI? Should these names be stable across reboots / kernel
> > upgrades? =20
>=20
> Stable in what exact way?

Example:
- Board has an ethernet PHYs that is described in DT, and therefore
  has stable sysfs path (derived from DT path), something like
    /sys/devices/.../mdio_bus/f1072004.mdio-mii/f1072004.mdio-mii:01

- The PHY has a subnode describing a LED.
  The LED subsystem has a different naming scheme (it uses DT node name
  as a last resort). When everything is okay, the dev_name() of the LED
  will be something like
    ethphy42:green:link

- Now suppose that the PHY driver is unloaded and loaded again. The PHY
  sysfs path is unchanged, but the LED will now be named
    ethphy43:green:link

Is this OK?

> Numbering of devices (where a dynamic value is part of a name, like the
> "42" in "usb42"), is never guaranteed to be stable, but the non-number
> part of the name (like "usb" is in "usb42") is stable, as that is what
> you have properly documented in the Documentation/ABI/ files defining
> the bus and class devices, right?

It does make sense for removable devices like USB. What I am asking
is whether it is also OK for devices that have stable DT nodes.

Marek