linux-kernel - Re: [PATCH v6 3/6] rust: irq: add support for non-threaded IRQs and handlers

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Message-ID: <d6e62068-a05a-43cf-ace3-ff7a41e9a1d7@de.bosch.com>
Date: Mon, 14 Jul 2025 09:57:11 +0200
From: Dirk Behme <dirk.behme@...bosch.com>
To: Danilo Krummrich <dakr@...nel.org>, Daniel Almeida
	<daniel.almeida@...labora.com>
CC: Benno Lossin <lossin@...nel.org>, Miguel Ojeda <ojeda@...nel.org>, "Alex
 Gaynor" <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, Gary Guo
	<gary@...yguo.net>, Björn Roy Baron
	<bjorn3_gh@...tonmail.com>, Andreas Hindborg <a.hindborg@...nel.org>, "Alice
 Ryhl" <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, "Greg
 Kroah-Hartman" <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
	<rafael@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Bjorn Helgaas
	<bhelgaas@...gle.com>, Krzysztof Wilczyński
	<kwilczynski@...nel.org>, <linux-kernel@...r.kernel.org>,
	<rust-for-linux@...r.kernel.org>, <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v6 3/6] rust: irq: add support for non-threaded IRQs and
 handlers

On 13/07/2025 16:19, Danilo Krummrich wrote:
> On Sun Jul 13, 2025 at 4:09 PM CEST, Daniel Almeida wrote:
>> On a second look, I wonder how useful this will be.
>>
>>  fn handle(&self, dev: &Device<Bound>) -> IrqReturn
>>
>> Sorry for borrowing this terminology, but here we offer Device<Bound>, while I
>> suspect that most drivers will be looking for the most derived Device type
>> instead. So for drm drivers this will be drm::Device, for example, not the base
>> dev::Device type. I assume that this pattern will hold for other subsystems as
>> well.
>>
>> Which brings me to my second point: drivers can store an ARef<drm::Device> on
>> the handler itself, and I assume that the same will be possible in other
>> subsystems.
> 
> Well, the whole point is that you can use a &Device<Bound> to directly access
> device resources without any overhead, i.e.
> 
> 	fn handle(&self, dev: &Device<Bound>) -> IrqReturn {
> 	   let io = self.iomem.access(dev);
> 
> 	   io.write32(...);

As this is exactly the example I was discussing privately with Daniel
(many thanks!), independent on the device discussion here, just for my
understanding:

Is it ok to do a 'self.iomem.access(dev)' at each interrupt? Wouldn't it
be cheaper/faster to pass 'io' instead of 'iomem' to the interrupt handler?

fn handle(...) -> IrqReturn {

    self.io.write32(...);

?

Thanks

Dirk