On Mon, 4 Oct 2021 09:10:35 +0200 Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > On Mon, Oct 04, 2021 at 09:04:38AM +0200, Marek Behún wrote: > > Hi Greg, > > > > On Mon, 4 Oct 2021 08:37:37 +0200 > > Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > On Sun, Oct 03, 2021 at 10:53:38PM +0200, Marek Behún wrote: > > > > Hello Greg, > > > > > > > > could you give your opinion on this discussion? > > > > > > 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? > > > > > > 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 > > None of the numbers there are "stable", right? > > > - 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 > > Wonderful, but the "42" means nothing. > > > - 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? > > Yup! > > The "link" should point to the device it is associated with, right? You > need to have some way to refer to the device. > > > > 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. > > Any device can be "removed" from the system and added back thanks to the > joy of the driver model :) > > Also, what prevents your DT from renumbering things in an update to it > in the future? The kernel doesn't care, and userspace should be able to > handle it. > > Again, any numbering scheme is NEVER stable, just because it feels like > it is at the moment for your device, you should NEVER rely on that, but > instead rely on the attributes of the device to determine what it is and > where it is in the device hierarchy (serial number, position location, > partition name, etc.) in order to know what it associated with. > > And again, this is 1/2 of the whole reason _why_ we created the unified > driver model in the kernel. Don't try to go back to the nightmare that > we had in the 2.4 and earlier kernel days please. OK, thanks Greg. This simplifies things. I shall send another version of LEDs under ethernet PHYs soon :) Marek
