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Message-ID: <6a16f0023b62beba4658677bebcc4786da1ea4be.camel@redhat.com>
Subject: Re: [PATCH 2/4] WIP: drm: Introduce rvkms
From: Lyude Paul <lyude@redhat.com>
To: Benno Lossin <benno.lossin@proton.me>, dri-devel@lists.freedesktop.org
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>, Maxime Ripard
 <mripard@kernel.org>, Thomas Zimmermann <tzimmermann@suse.de>, David Airlie
 <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>, Miguel Ojeda
 <ojeda@kernel.org>, Alex Gaynor <alex.gaynor@gmail.com>, Wedson Almeida
 Filho <wedsonaf@gmail.com>, Boqun Feng <boqun.feng@gmail.com>, Gary Guo
 <gary@garyguo.net>, =?ISO-8859-1?Q?Bj=F6rn?= Roy Baron
 <bjorn3_gh@protonmail.com>, Andreas Hindborg <a.hindborg@samsung.com>,
 Alice Ryhl <aliceryhl@google.com>, linux-kernel@vger.kernel.org,
 rust-for-linux@vger.kernel.org
Date: Sun, 21 Apr 2024 21:54:25 -0400
In-Reply-To: <b41f707d-7e06-4c1a-93f0-d74ee242b650@proton.me>
References: <20240322221305.1403600-1-lyude@redhat.com>
	 <20240322221305.1403600-3-lyude@redhat.com>
	 <b41f707d-7e06-4c1a-93f0-d74ee242b650@proton.me>
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On Wed, 2024-03-27 at 21:06 +0000, Benno Lossin wrote:
> On 22.03.24 23:03, Lyude Paul wrote:
> > diff --git a/drivers/gpu/drm/rvkms/connector.rs
> > b/drivers/gpu/drm/rvkms/connector.rs
> > new file mode 100644
> > index 0000000000000..40f84d38437ee
> > --- /dev/null
> > +++ b/drivers/gpu/drm/rvkms/connector.rs
> > @@ -0,0 +1,55 @@
> > +// TODO: License and stuff
> > +// Contain's rvkms's drm_connector implementation
> > +
> > +use super::{RvkmsDriver, RvkmsDevice, MAX_RES, DEFAULT_RES};
> > +use kernel::{
> > +=C2=A0=C2=A0=C2=A0 prelude::*,
> > +=C2=A0=C2=A0=C2=A0 drm::{
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 device::Device,
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 kms::{
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 con=
nector::{self, ConnectorGuard},
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Mod=
eConfigGuard
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 }
> > +=C2=A0=C2=A0=C2=A0 },
> > +=C2=A0=C2=A0=C2=A0 prelude::*
> > +};
> > +use core::marker::PhantomPinned;
> > +
> > +#[pin_data]
> > +pub(crate) struct DriverConnector {
> > +=C2=A0=C2=A0=C2=A0 #[pin]
> > +=C2=A0=C2=A0=C2=A0 _p: PhantomPinned
> > +}
>=20
> This struct does not need to be annotated with `#[pin_data]`, this
> should just work:
>=20
> pub(crate) struct DriverConnector;
>=20
> > +
> > +pub(crate) type Connector =3D connector::Connector<DriverConnector>;
> > +
> > +impl connector::DriverConnector for DriverConnector {
> > +=C2=A0=C2=A0=C2=A0 type Initializer =3D impl PinInit<Self, Error>;
> > +
> > +=C2=A0=C2=A0=C2=A0 type State =3D ConnectorState;
> > +
> > +=C2=A0=C2=A0=C2=A0 type Driver =3D RvkmsDriver;
> > +
> > +=C2=A0=C2=A0=C2=A0 type Args =3D ();
> > +
> > +=C2=A0=C2=A0=C2=A0 fn new(dev: &Device<Self::Driver>, args: Self::Args=
) ->
> > Self::Initializer {
>=20
> And then here just return `Self`.
>=20
> This works, since there is a blanket impl `PinInit<T, E> for T`.
>=20
> 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=3Dvblan=
k#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.

>=20

--=20
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat