linux-kernel - Re: [PATCH v2 00/10] Device / Driver and PCI Rust abstractions

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Date: Wed, 19 Jun 2024 14:42:34 +0200
From: Danilo Krummrich <dakr@...hat.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: Viresh Kumar <viresh.kumar@...aro.org>, rafael@...nel.org,
	bhelgaas@...gle.com, ojeda@...nel.org, alex.gaynor@...il.com,
	wedsonaf@...il.com, boqun.feng@...il.com, gary@...yguo.net,
	bjorn3_gh@...tonmail.com, benno.lossin@...ton.me,
	a.hindborg@...sung.com, aliceryhl@...gle.com, airlied@...il.com,
	fujita.tomonori@...il.com, lina@...hilina.net, pstanner@...hat.com,
	ajanulgu@...hat.com, lyude@...hat.com, robh@...nel.org,
	daniel.almeida@...labora.com, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	Manos Pitsidianakis <manos.pitsidianakis@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH v2 00/10] Device / Driver and PCI Rust abstractions

On Wed, Jun 19, 2024 at 02:17:58PM +0200, Greg KH wrote:
> On Wed, Jun 19, 2024 at 05:34:07PM +0530, Viresh Kumar wrote:
> > On 19-06-24, 01:39, Danilo Krummrich wrote:
> > > - move base device ID abstractions to a separate source file (Greg)
> > > - remove `DeviceRemoval` trait in favor of using a `Devres` callback to
> > >   unregister drivers
> > > - remove `device::Data`, we don't need this abstraction anymore now that we
> > >   `Devres` to revoke resources and registrations
> > 
> > Hi Danilo,
> > 
> > I am working on writing bindings for CPUFreq drivers [1] and was
> > looking to rebase over staging/rust-device, and I am not sure how to
> > proceed after device::Data is dropped now.
> 
> As it should be dropped :)
> 
> A struct device does not have a "data" pointer, it has specific other
> pointers to hold data in, but they better be accessed by their proper
> name if you want rust code to be reviewable by anyone.
> 
> Also, you shouldn't be accessing that field directly anyway, that's what
> the existing dev_set_drvdata/dev_get_drvdata() calls are for.  Just use
> them please.

Sorry that this was confusing. `device::Data` was a generic type for drivers to
store their private data in. It was meant to be handled by subsystems to store
it in their particular driver structure. Is most cases of course this eventually
ends up in a call to dev_set_drvdata() (e.g. through pci_set_drvdata()).

The reason we had this in the first place was that `device::Data` was also used
to store resources and registrations. With my rework to `Devres` this isn't the
case anymore, and hence `device::Data` does not add any value anymore and was
removed.

> 
> thanks,
> 
> greg k-h
>