linux-kernel - Re: [RFC PATCH 0/3] gpu: nova-core: add basic timer subdevice implementation

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Message-ID: <20250228185008.GG39591@nvidia.com>
Date: Fri, 28 Feb 2025 14:50:08 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Dave Airlie <airlied@...il.com>
Cc: John Hubbard <jhubbard@...dia.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Alexandre Courbot <acourbot@...dia.com>,
	Gary Guo <gary@...yguo.net>,
	Joel Fernandes <joel@...lfernandes.org>,
	Boqun Feng <boqun.feng@...il.com>, Ben Skeggs <bskeggs@...dia.com>,
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
	nouveau@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	paulmck@...nel.org
Subject: Re: [RFC PATCH 0/3] gpu: nova-core: add basic timer subdevice
 implementation

On Fri, Feb 28, 2025 at 02:10:39PM +1000, Dave Airlie wrote:
> On Fri, 28 Feb 2025 at 09:07, John Hubbard <jhubbard@...dia.com> wrote:
> >
> > On Thu Feb 27, 2025 at 1:42 PM PST, Dave Airlie wrote:
> > > On Thu, 27 Feb 2025 at 11:34, John Hubbard <jhubbard@...dia.com> wrote:
> > >> On Wed Feb 26, 2025 at 5:02 PM PST, Greg KH wrote:
> > >> > On Wed, Feb 26, 2025 at 07:47:30PM -0400, Jason Gunthorpe wrote:
> > ...
> > > nova is just a drm driver, it's not a rewrite of the drm subsystem,
> > > that sort of effort would entail a much larger commitment.
> >
> > Maybe at this point in the discussion it would help to discern between
> > nova-core and nova-drm:
> >
> >     drivers/gpu/nova-core/ (under discussion here)
> 
> nova-core won't be suffering any of the issues Jason is raising,
> nova-core isn't going to have userspace facing interfaces or be part
> of any subsystem with major lifetime expectations. It has to deal with
> the hardware going away due to hot unplugs, and that is what this
> devres is for.

It will suffer the general problem because it provides interfaces to
the nova DRM module and DRM will hold a reference on it's 'nova core
object' till the DRM file_operations release.

So you end up with nova core remove running and being unable to clean
things because of that DRM reference, even though the nova DRM driver
has completed remove.

You could wrap the nova core reference in a devres, but I think that
would be objectionable. :)

Though I expect no module EAF because you'd be direct linking..

Jason