Message-ID: <20250729114934.GK402218@unreal>
Date: Tue, 29 Jul 2025 14:49:34 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Sean Anderson <sean.anderson@...ux.dev>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ira Weiny <ira.weiny@...el.com>, linux-kernel@...r.kernel.org,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Dave Ertman <david.m.ertman@...el.com>
Subject: Re: [PATCH] auxiliary: Automatically generate id

On Tue, Jul 29, 2025 at 01:28:14PM +0200, Danilo Krummrich wrote:
> On Tue Jul 29, 2025 at 1:11 PM CEST, Leon Romanovsky wrote:
> > On Tue, Jul 29, 2025 at 12:51:42PM +0200, Danilo Krummrich wrote:
> >> On Tue Jul 29, 2025 at 12:01 PM CEST, Leon Romanovsky wrote:
> >> > On Tue, Jul 29, 2025 at 11:36:27AM +0200, Danilo Krummrich wrote:
> >> >> On Mon Jul 28, 2025 at 11:10 PM CEST, Sean Anderson wrote:
> >> >> > As it turns out, ids are not allowed to have semantic meaning. Their
> >> >> > only purpose is to prevent sysfs collisions. To simplify things, just
> >> >> > generate a unique id for each auxiliary device. Remove all references to
> >> >> > filling in the id member of the device.
> >> >> >
> >> >> > Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
> >> >> > ---
> >> >> >
> >> >> >  drivers/base/auxiliary.c      | 32 +++++++++++++++++++++++---------
> >> >> >  include/linux/auxiliary_bus.h | 26 ++++++++------------------
> >> >> >  2 files changed, 31 insertions(+), 27 deletions(-)
> >> >> >
> >> >> > diff --git a/drivers/base/auxiliary.c b/drivers/base/auxiliary.c
> >> >> > index dba7c8e13a53..f66067df03ad 100644
> >> >> > --- a/drivers/base/auxiliary.c
> >> >> > +++ b/drivers/base/auxiliary.c
> >> >> > @@ -264,6 +264,8 @@ static const struct bus_type auxiliary_bus_type = {
> >> >> >  	.pm = &auxiliary_dev_pm_ops,
> >> >> >  };
> >> >> >  
> >> >> > +static DEFINE_IDA(auxiliary_id);
> >> >> 
> >> >> I think this is the correct thing to do, even though the per device IDA drivers
> >> >> typically went for so far produces IDs that are easier to handle when debugging
> >> >> things.
> >> >> 
> >> >> > +
> >> >> >  /**
> >> >> >   * auxiliary_device_init - check auxiliary_device and initialize
> >> >> >   * @auxdev: auxiliary device struct
> >> >> > @@ -331,20 +333,37 @@ int __auxiliary_device_add(struct auxiliary_device *auxdev, const char *modname)
> >> >> >  		return -EINVAL;
> >> >> >  	}
> >> >> >  
> >> >> > +	ret = ida_alloc(&auxiliary_id, GFP_KERNEL);
> >> >> > +	if (ret < 0) {
> >> >> > +		dev_err(dev, "auxiliary device id_alloc fauiled: %d\n", ret);
> >> >> > +		return ret;
> >> >> > +	}
> >> >> > +	auxdev->id = ret;
> >> >> 
> >> >> This overwrites the ID number set by various drivers that (still) use the
> >> >> auxiliary_device_init() and auxiliary_device_add() pair.
> >> >> 
> >> >> While I agree with the general intent, I think it's a very bad idea to just
> >> >> perform this change silently leaving drivers with their IDA instances not
> >> >> knowing that the set ID numbers do not have an effect anymore.
> >> >> 
> >> >> I think this should be multiple steps:
> >> >> 
> >> >>   (1) Remove the id parameter and force an internal ID only for
> >> >>       auxiliary_device_create().
> >> >> 
> >> >>   (2) Convert applicable drivers (and the Rust abstraction) to use
> >> >>       auxiliary_device_create() rather than auxiliary_device_init() and
> >> >>       auxiliary_device_add().
> >> >> 
> >> >>   (3) Treewide change to force an internal ID for all auxiliary devices
> >> >>       considering this change in all affected drivers.
> >> >
> >> > I would suggest easier approach.
> >> > 1. Add to the proposal patch, the sed generated line which removes auxdev->id
> >> > assignment in the drivers.
> >> > Something like this from mlx5:
> >> >  - sf_dev->adev.id = id;
> >> >
> >> > 2. Add standalone patches to remove not used ida_alloc/ida_free calls
> >> > from the drivers.
> >> 
> >> I assume you suggest this as an alternative to (3) above? If so, that's what I
> >> meant in (3), I should have written "treewide series" instead of "treewide
> >> change".
> >
> > I would say for all steps. Very important reason to use
> > auxiliary_device_init() and not auxiliary_device_create() is to bind
> > custom release callback, which is needed to release private data.
> >
> > In addition, complex devices embed struct auxiliary_device in their
> > internal struct to rely on container_of to access the data.
> > See mlx5_sf_dev_add() in drivers/net/ethernet/mellanox/mlx5/core/sf/dev/dev.c
> > as an example.
> 
> That's why I said "*applicable* drivers" everywhere. :)
> 
> The examples you mention don't fall under this category, but in general drivers
> that *can* use auxiliary_device_create() should do it.

Of course, the thing is that even drivers with auxiliary_device_init()
shouldn't set "id" and because they need to be updated.

The auxiliary_device_create() relies on auxiliary_device_init() under the hood,
so most likely the change should be there.

> 
> >> Technically (2) is orthogonal, yet I think it's a bit better to do the desired
> >> change right away. Otherwise we end up converting all applicable drivers to
> >> implement the auxiliary device release callback (which we need for a common
> >> ida_free()) first, just to remove it later on when we convert to
> >> auxiliary_device_create().
> >
> > My expectation is to see extension of driver/base/core.c. Something like that:
> >
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index cbc0099d8ef24..63847c84dbdc0 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -2560,8 +2560,10 @@ static void device_release(struct kobject *kobj)
> >
> >         kfree(dev->dma_range_map);
> >
> > -       if (dev->release)
> > +       if (dev->release) {
> > +               dev->bus_specific_cleanup(dev);
> >                 dev->release(dev);
> > +       }
> >         else if (dev->type && dev->type->release)
> >                 dev->type->release(dev);
> >         else if (dev->class && dev->class->dev_release)
> 
> The common pattern is to have custom release callbacks for class or bus specific
> device types.
> 
> In this case drivers would set struct auxiliary_device::release. And the
> auxiliary bus would implement the underlying struct device::release to call the
> driver provided struct auxiliary_device::release plus the additional cleanup.
> 
> What you propose works as well, but it moves bus or class device specifics into
> the generic struct device, where the normal inheritance pattern already solves
> this.

It was just a sketch, everything that allows to set custom release
callback is fine by me.

Thanks

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