linux-kernel - Re: [PATCH 2/4] WIP: drm: Introduce rvkms

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Date: Thu, 25 Apr 2024 15:46:14 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Lyude Paul <lyude@...hat.com>, dri-devel@...ts.freedesktop.org
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, Wedson Almeida Filho <wedsonaf@...il.com>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, Andreas Hindborg <a.hindborg@...sung.com>, Alice Ryhl <aliceryhl@...gle.com>, linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 2/4] WIP: drm: Introduce rvkms

On 22.04.24 03:54, Lyude Paul wrote:
> On Wed, 2024-03-27 at 21:06 +0000, Benno Lossin wrote:
>> On 22.03.24 23:03, Lyude Paul wrote:
>>> +
>>> +pub(crate) type Connector = connector::Connector<DriverConnector>;
>>> +
>>> +impl connector::DriverConnector for DriverConnector {
>>> +    type Initializer = impl PinInit<Self, Error>;
>>> +
>>> +    type State = ConnectorState;
>>> +
>>> +    type Driver = RvkmsDriver;
>>> +
>>> +    type Args = ();
>>> +
>>> +    fn new(dev: &Device<Self::Driver>, args: Self::Args) ->
>>> Self::Initializer {
>>
>> And then here just return `Self`.
>>
>> This works, since there is a blanket impl `PinInit<T, E> for T`.
>>
>> Looking at how you use this API, I am not sure if you actually need
>> pin-init for the type that implements `DriverConnector`.
>> Do you need to store eg `Mutex<T>` or something else that needs
>> pin-init in here in a more complex driver?
> 
> Most likely yes - a lot of drivers have various private locks contained
> within their subclassed mode objects. I'm not sure we will in rvkms's
> connector since vkms doesn't really do much with connectors - but we at
> a minimum be using pinned types (spinlocks and hrtimers) in our
> DriverCrtc implementation once I've started implementing support for
> vblanks[1]
> 
> [1]
> https://www.kernel.org/doc/html/v6.9-rc5/gpu/drm-kms.html?highlight=vblank#vertical-blanking
> 
> In nova (the main reason I'm working on rvkms in the first place),
> we'll definitely have locks in our connectors and possibly other types.

I see, in that case it would be a good idea to either have an RFC of
the nova driver (or something else that needs pinned types) as
motivation for why it needs to be pin-initialized.

-- 
Cheers,
Benno