linux-kernel - Re: [PATCH v3 12/19] gpu: nova-core: add helper function to wait on condition

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Message-ID: <aCNcQ835i40UUW--@pollux>
Date: Tue, 13 May 2025 16:50:43 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Alexandre Courbot <acourbot@...dia.com>
Cc: 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>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Jonathan Corbet <corbet@....net>,
	John Hubbard <jhubbard@...dia.com>, Ben Skeggs <bskeggs@...dia.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Timur Tabi <ttabi@...dia.com>, Alistair Popple <apopple@...dia.com>,
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
	nouveau@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v3 12/19] gpu: nova-core: add helper function to wait on
 condition

On Wed, May 07, 2025 at 10:52:39PM +0900, Alexandre Courbot wrote:
> While programming the hardware, we frequently need to busy-wait until
> a condition (like a given bit of a register to switch value) happens.
> 
> Add a basic `wait_on` helper function to wait on such conditions
> expressed as a closure, with a timeout argument.
> 
> This is temporary as we will switch to `read_poll_timeout` [1] once it
> is available.
> 
> [1] https://lore.kernel.org/lkml/20250220070611.214262-8-fujita.tomonori@gmail.com/
> 
> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
> ---
>  drivers/gpu/nova-core/util.rs | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/drivers/gpu/nova-core/util.rs b/drivers/gpu/nova-core/util.rs
> index 332a64cfc6a9d7d787fbdc228887c0be53a97160..afb525228431a2645afe7bb34988e9537757b1d7 100644
> --- a/drivers/gpu/nova-core/util.rs
> +++ b/drivers/gpu/nova-core/util.rs
> @@ -1,5 +1,10 @@
>  // SPDX-License-Identifier: GPL-2.0
>  
> +use core::time::Duration;
> +
> +use kernel::prelude::*;
> +use kernel::time::Ktime;
> +
>  pub(crate) const fn to_lowercase_bytes<const N: usize>(s: &str) -> [u8; N] {
>      let src = s.as_bytes();
>      let mut dst = [0; N];
> @@ -19,3 +24,28 @@ pub(crate) const fn const_bytes_to_str(bytes: &[u8]) -> &str {
>          Err(_) => kernel::build_error!("Bytes are not valid UTF-8."),
>      }
>  }
> +
> +/// Wait until `cond` is true or `timeout` elapsed.
> +///
> +/// When `cond` evaluates to `Some`, its return value is returned.
> +///
> +/// `Err(ETIMEDOUT)` is returned if `timeout` has been reached without `cond` evaluating to
> +/// `Some`.
> +///
> +/// TODO: replace with `read_poll_timeout` once it is available.
> +/// (https://lore.kernel.org/lkml/20250220070611.214262-8-fujita.tomonori@gmail.com/)
> +#[expect(dead_code)]
> +pub(crate) fn wait_on<R, F: Fn() -> Option<R>>(timeout: Duration, cond: F) -> Result<R> {
> +    let start_time = Ktime::ktime_get();
> +
> +    loop {
> +        if let Some(ret) = cond() {
> +            return Ok(ret);
> +        }
> +
> +        let cur_time = Ktime::ktime_get();
> +        if (cur_time - start_time).to_ns() > timeout.as_nanos() as i64 {
> +            return Err(ETIMEDOUT);
> +        }
> +    }
> +}

NIT: Can't you use this for wait_gfw_boot_completion() too?