linux-kernel - Re: [PATCH v4 1/2] driver core: Introduce device_link_wait

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Message-ID: <f42ceee61ddb8b50c347589649d4131476ab5d81.camel@gmail.com>
Date: Wed, 06 Mar 2024 16:13:15 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: Herve Codina <herve.codina@...tlin.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, Rob Herring <robh+dt@...nel.org>, Frank
 Rowand <frowand.list@...il.com>, Saravana Kannan <saravanak@...gle.com>,
 Lizhi Hou <lizhi.hou@....com>, Max Zhen <max.zhen@....com>, Sonal Santan
 <sonal.santan@....com>, Stefano Stabellini <stefano.stabellini@...inx.com>,
  Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, Allan Nielsen
 <allan.nielsen@...rochip.com>, Horatiu Vultur
 <horatiu.vultur@...rochip.com>, Steen Hegelund
 <steen.hegelund@...rochip.com>, Luca Ceresoli <luca.ceresoli@...tlin.com>,
 Nuno Sa <nuno.sa@...log.com>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>,  stable@...r.kernel.org
Subject: Re: [PATCH v4 1/2] driver core: Introduce device_link_wait_removal()

On Wed, 2024-03-06 at 16:01 +0100, Herve Codina wrote:
> Hi Nuno,
> 
> On Wed, 06 Mar 2024 15:50:44 +0100
> Nuno Sá <noname.nuno@...il.com> wrote:
> 
> ...
> > > > > > 
> > > > > > That makes sense but then the only thing I still don't fully get is
> > > > > > why
> > > > > > we
> > > > > > have
> > > > > > a separate devlink_class_init() initcall for registering the devlink
> > > > > > class
> > > > > > (which can also fail)...  
> > > > > 
> > > > > Well, I haven't added it. :-)
> > > > >   
> > > > > > What I take from the above is that we should fail the
> > > > > > driver model if one of it's fundamental components fails so I would
> > > > > > say
> > > > > > we
> > > > > > should merge devlink_class_init() with device_init() otherwise it's
> > > > > > a
> > > > > > bit
> > > > > > confusing (at least to me) and gives the idea that it's ok for the
> > > > > > driver
> > > > > > model
> > > > > > to exist without the links (unless I'm missing some other reason for
> > > > > > the
> > > > > > devlink
> > > > > > init function).  
> > > > > 
> > > > > +1
> > > > > 
> > > > > Feel free to send a patch along these lines, chances are that it will
> > > > > be popular. ;-)  
> > > > 
> > > > I was actually thinking about that but I think I encountered the reason
> > > > why
> > > > we
> > > > have it like this... devices_init() is called from driver_init() and
> > > > there
> > > > we
> > > > have:
> > > > 
> > > > ...
> > > > 
> > > > devices_init();
> > > > buses_init();
> > > > classes_init();
> > > > 
> > > > ...
> > > > 
> > > > So classes are initialized after devices which means we can't really do
> > > > class_register(&devlink_class) from devices_init(). Unless, of course,
> > > > we
> > > > re-
> > > > order things in driver_init() but that would be a questionable change at
> > > > the
> > > > very least.
> > > > 
> > > > So, while I agree with what you've said, I'm still not sure if mixing
> > > > devlink
> > > > stuff between devices_init() and devlink_class_init() is the best thing
> > > > to
> > > > do
> > > > given that we already have the case where devlink_class_init() can fail
> > > > while
> > > > the driver model is up.  
> > > 
> > > So why don't you make devlink_class_init() do a BUG() on failure
> > > instead of returning an error?  IMO crashing early is better than
> > > crashing later or otherwise failing in a subtle way due to a missed
> > > dependency.  
> > 
> > Well, I do agree with that... Maybe that's something that Herve can sneak in
> > this patch? Otherwise, I can later (after this one is applied) send a patch
> > for
> > it.
> 
> Well, I don't thing that this have to be part of this current series.
> It is an other topic and should be handled out of this current series.
> 

Yeah, fair enough... IMHO, then I would say that we should still have the
workqueue moved to devlink_class_init() and I can then follow up with a patch to
do BUG_ON(ret) in it.

Alternatively I can also just move it in the follow up patch but I don't think
it makes much sense.

- Nuno Sá