Received-SPF: pass (google.com: domain of linux-kernel+bounces-96285-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
From: "Daniel Almeida" <daniel.almeida@collabora.com>
In-Reply-To: <c70935815ffc29ae5256b94c0e4880952abad79c.camel@ndufresne.ca>
Content-Type: text/plain; charset="utf-8"
References: <20240227215146.46487-1-daniel.almeida@collabora.com>
	 <20240307190841.10260-1-daniel.almeida@collabora.com>
	 <20240307190841.10260-3-daniel.almeida@collabora.com> <c70935815ffc29ae5256b94c0e4880952abad79c.camel@ndufresne.ca>
Date: Thu, 07 Mar 2024 21:45:33 +0000
Cc: wedsonaf@gmail.com, ojeda@kernel.org, mchehab@kernel.org, hverkuil@xs4all.nl, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, kernel@collabora.com
To: "Nicolas Dufresne" <nicolas@ndufresne.ca>
Precedence: bulk
MIME-Version: 1.0
Message-ID: <144b27-65ea3580-f-61876d80@130641868>
Subject: =?utf-8?q?Re=3A?= [RFC PATCH v2 2/2] =?utf-8?q?media=3A?=
 =?utf-8?q?_rkvdec=3A?= rewrite parts of the driver in Rust
User-Agent: SOGoMail 5.10.0
Content-Transfer-Encoding: quoted-printable

Hi Nicolas,

> struct reg123 {
>   val1 :3  // bit 31-29
>   val2 :20 // bit 28-9
>   val3 :9  // bit 8-0
> };

What you're describing can be modeled as Ranges in Rust:

```
use core::ops::Range;

struct Foo {
    reg1: Range<u32>,
    reg2: Range<u32>,
    reg3: Range<u32>
}

const FOO=5FREGMAP: Foo =3D Foo {
        reg1: 0..3,
        reg2: 3..24,
        reg3: 24..32
};
```

It becomes more useful when you pair that with a bit writer. For an exa=
mple of previous art, see Faith's work: [0]

This has asserts in the right places so that you do not shoot yourself =
in the foot. IMHO, such a data structure can be shared with the whole R=
ust code in the kernel.

You can then describe your writes using the ranges, e.g.: [1]=20

But as we've established, instead of writing the ranges down directly, =
you can simply refer to them as FOO=5FREGMAP.reg1, FOO=5FREGMAP.reg2 an=
d so on.

I believe this is both more readable and safer.

[0]: https://gitlab.freedesktop.org/mesa/mesa/-/blob/main/src/nouveau/c=
ompiler/bitview/lib.rs?ref=5Ftype=3Dheads

[1]: https://gitlab.freedesktop.org/mesa/mesa/-/blob/main/src/nouveau/c=
ompiler/nak/encode=5Fsm70.rs?ref=5Ftype=3Dheads#L228