linux-kernel - Re: [PATCH 1/2] drm/panic: use `div

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Message-ID: <7fa51125-3015-446a-93b1-57b07a7ee8f5@redhat.com>
Date: Mon, 10 Mar 2025 08:49:51 +0100
From: Jocelyn Falempe <jfalempe@...hat.com>
To: Miguel Ojeda <ojeda@...nel.org>, Thomas Böhler
 <witcher@...edspace.de>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Alex Gaynor <alex.gaynor@...il.com>
Cc: dri-devel@...ts.freedesktop.org, Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>,
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, rust-for-linux@...r.kernel.org,
 linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH 1/2] drm/panic: use `div_ceil` to clean Clippy warning

On 02/03/2025 00:16, Miguel Ojeda wrote:
> Starting with the upcoming Rust 1.86.0 (to be released 2025-04-03),
> Clippy warns:
> 
>      error: manually reimplementing `div_ceil`
>         --> drivers/gpu/drm/drm_panic_qr.rs:548:26
>          |
>      548 |         let pad_offset = (offset + 7) / 8;
>          |                          ^^^^^^^^^^^^^^^^ help: consider using `.div_ceil()`: `offset.div_ceil(8)`
>          |
>          = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_div_ceil
> 
> And similarly for `stride`. Thus apply the suggestion to both.
> 
> The behavior (and thus codegen) is not exactly equivalent [1][2], since
> `div_ceil()` returns the right value for the values that currently
> would overflow.

I pushed both patches to drm-misc-fixes, with the "Cc" tag added.

Thanks a lot for your contributions.

-- 

Jocelyn
> 
> Link: https://github.com/rust-lang/rust-clippy/issues/14333 [1]
> Link: https://godbolt.org/z/dPq6nGnv3 [2]
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
> ---
>   drivers/gpu/drm/drm_panic_qr.rs | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panic_qr.rs b/drivers/gpu/drm/drm_panic_qr.rs
> index bcf248f69252..8bb5e52d75cc 100644
> --- a/drivers/gpu/drm/drm_panic_qr.rs
> +++ b/drivers/gpu/drm/drm_panic_qr.rs
> @@ -545,7 +545,7 @@ fn add_segments(&mut self, segments: &[&Segment<'_>]) {
>           }
>           self.push(&mut offset, (MODE_STOP, 4));
>   
> -        let pad_offset = (offset + 7) / 8;
> +        let pad_offset = offset.div_ceil(8);
>           for i in pad_offset..self.version.max_data() {
>               self.data[i] = PADDING[(i & 1) ^ (pad_offset & 1)];
>           }
> @@ -659,7 +659,7 @@ struct QrImage<'a> {
>   impl QrImage<'_> {
>       fn new<'a, 'b>(em: &'b EncodedMsg<'b>, qrdata: &'a mut [u8]) -> QrImage<'a> {
>           let width = em.version.width();
> -        let stride = (width + 7) / 8;
> +        let stride = width.div_ceil(8);
>           let data = qrdata;
>   
>           let mut qr_image = QrImage {
> 
> base-commit: d082ecbc71e9e0bf49883ee4afd435a77a5101b6