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

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Message-ID: <Z8ChnwPC0UwM8xBe@cassiopeiae>
Date: Thu, 27 Feb 2025 18:32:15 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Boqun Feng <boqun.feng@...il.com>, Jason Gunthorpe <jgg@...dia.com>
Cc: Joel Fernandes <joelagnelf@...dia.com>,
	Alexandre Courbot <acourbot@...dia.com>,
	Dave Airlie <airlied@...il.com>, Gary Guo <gary@...yguo.net>,
	Joel Fernandes <joel@...lfernandes.org>,
	John Hubbard <jhubbard@...dia.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 Thu, Feb 27, 2025 at 08:55:09AM -0800, Boqun Feng wrote:
> On Thu, Feb 27, 2025 at 12:17:33PM -0400, Jason Gunthorpe wrote:
> 
> > I still wonder why you couldn't also have these reliable reference
> > counts rooted on the device driver instead of only on the module.
> > 
> 
> You could put reliable reference counts anywhere you want, as long as it
> reflects the resource dependencies.

Right, as I explained in a different reply, the signature for PCI driver probe()
looks like this:

	fn probe(pdev: &mut pci::Device, _info: &Self::IdInfo) -> Result<Pin<KBox<Self>>>

The returned Pin<KBox<Self>> has the lifetime of the driver being bound to the
device.

Which means a driver can bind things to this lifetime. But, it isn't forced to,
it can also put things into an Arc and share it with the rest of the world.

If something is crucial to be bound to the lifetime of a driver being bound to a
device (i.e. device resources), you have to expose it as Devres<T>.

Subsequently, you can put the Devres<T> in an Arc and do whatever you want, the
result will still be that T is dropped once the device is unbound.