From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9181CC369C2 for ; Tue, 22 Apr 2025 12:07:37 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 7406C10E573; Tue, 22 Apr 2025 12:07:35 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.b="WolUm2gA"; dkim-atps=neutral Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by gabe.freedesktop.org (Postfix) with ESMTPS id 370A510E573; Tue, 22 Apr 2025 12:07:34 +0000 (UTC) Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 01B095C5ADB; Tue, 22 Apr 2025 12:05:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EB460C4CEE9; Tue, 22 Apr 2025 12:07:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1745323644; bh=OBfe8Ek/fGIsqzH06Fvhs9ujpTLbbrgmmqi+5C8lSFM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=WolUm2gAGq8nDv4YvE6F04tDuvG1GnbnyDn84umwh1skDFc9xh4tfOlB6evHlIGc9 Sp/k8gkibf2f+E1b40TIwCmWunIv76a9F+mTFmINe9waw4TM+LjCwuR4pA+zvwRVgu ECfavh7fMc0Egfkjyhxt5Yh6RdMq35EvSMMTSGF4ME5ap6a3M19bjOBxPjW+Qdu0kI zCRysq9ZihBTHwI2ZAOarlfX2IGe1Tm/ZgljdJHJo3TV03vZjSPa82IBmCd6U1zAaa 6phezCpyjSETC/0Y+SILBSOtgMedJIq6zPkKpquK4A2Bz9/baN8Vspd1m3O950zn6R jm5it5cvaKTVQ== Date: Tue, 22 Apr 2025 14:07:17 +0200 From: Danilo Krummrich To: Alexandre Courbot Cc: Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , David Airlie , Simona Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Jonathan Corbet , John Hubbard , Ben Skeggs , Joel Fernandes , Timur Tabi , Alistair Popple , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org Subject: Re: [PATCH 10/16] gpu: nova-core: add basic timer device Message-ID: References: <20250420-nova-frts-v1-0-ecd1cca23963@nvidia.com> <20250420-nova-frts-v1-10-ecd1cca23963@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250420-nova-frts-v1-10-ecd1cca23963@nvidia.com> X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Sun, Apr 20, 2025 at 09:19:42PM +0900, Alexandre Courbot wrote: > Add a timer that works with GPU time and provides the ability to wait on > a condition with a specific timeout. What can this timer do for us, what and HrTimer can't do for us? > > The `Duration` Rust type is used to keep track is differences between > timestamps ; this will be replaced by the equivalent kernel type once it > lands. Fine for me -- can you please add a corresponding TODO and add it to your list of follow-up patches? > diff --git a/drivers/gpu/nova-core/timer.rs b/drivers/gpu/nova-core/timer.rs > new file mode 100644 > index 0000000000000000000000000000000000000000..8987352f4192bc9b4b2fc0fb5f2e8e62ff27be68 > --- /dev/null > +++ b/drivers/gpu/nova-core/timer.rs > @@ -0,0 +1,133 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +//! Nova Core Timer subdevice > + > +// To be removed when all code is used. > +#![allow(dead_code)] Please prefer 'expect'. > + > +use core::fmt::Display; > +use core::ops::{Add, Sub}; > +use core::time::Duration; > + > +use kernel::devres::Devres; > +use kernel::num::U64Ext; > +use kernel::prelude::*; > + > +use crate::driver::Bar0; > +use crate::regs; > + > +/// A timestamp with nanosecond granularity obtained from the GPU timer. > +/// > +/// A timestamp can also be substracted to another in order to obtain a [`Duration`]. > +#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)] > +pub(crate) struct Timestamp(u64); > + > +impl Display for Timestamp { > + fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result { > + write!(f, "{}", self.0) > + } > +} > + > +impl Add for Timestamp { > + type Output = Self; > + > + fn add(mut self, rhs: Duration) -> Self::Output { > + let mut nanos = rhs.as_nanos(); > + while nanos > u64::MAX as u128 { > + self.0 = self.0.wrapping_add(nanos as u64); > + nanos -= u64::MAX as u128; > + } > + > + Timestamp(self.0.wrapping_add(nanos as u64)) > + } > +} > + > +impl Sub for Timestamp { > + type Output = Duration; > + > + fn sub(self, rhs: Self) -> Self::Output { > + Duration::from_nanos(self.0.wrapping_sub(rhs.0)) > + } > +} > + > +pub(crate) struct Timer {} > + > +impl Timer { > + pub(crate) fn new() -> Self { > + Self {} > + } > + > + /// Read the current timer timestamp. > + pub(crate) fn read(&self, bar: &Bar0) -> Timestamp { > + loop { > + let hi = regs::PtimerTime1::read(bar); > + let lo = regs::PtimerTime0::read(bar); > + > + if hi.hi() == regs::PtimerTime1::read(bar).hi() { > + return Timestamp(u64::from_u32s(hi.hi(), lo.lo())); > + } So, if hi did not change since we've read both hi and lo, we can trust both values. Probably worth to add a brief comment. Additionally, we may want to add that if we get unlucky, it takes around 4s to get unlucky again, even though that's rather obvious. > + } > + } > + > + #[allow(dead_code)] > + pub(crate) fn time(bar: &Bar0, time: u64) { > + regs::PtimerTime1::default() > + .set_hi(time.upper_32_bits()) > + .write(bar); > + regs::PtimerTime0::default() > + .set_lo(time.lower_32_bits()) > + .write(bar); > + } > + > + /// Wait until `cond` is true or `timeout` elapsed, based on GPU time. > + /// > + /// When `cond` evaluates to `Some`, its return value is returned. > + /// > + /// `Err(ETIMEDOUT)` is returned if `timeout` has been reached without `cond` evaluating to > + /// `Some`, or if the timer device is stuck for some reason. > + pub(crate) fn wait_on Option>( > + &self, > + bar: &Devres, > + timeout: Duration, > + cond: F, > + ) -> Result { > + // Number of consecutive time reads after which we consider the timer frozen if it hasn't > + // moved forward. > + const MAX_STALLED_READS: usize = 16; Huh! Can't we trust the timer hardware? Probably one reason more to use HrTimer? > + > + let (mut cur_time, mut prev_time, deadline) = { > + let cur_time = with_bar!(bar, |b| self.read(b))?; > + let deadline = cur_time + timeout; > + > + (cur_time, cur_time, deadline) > + }; > + let mut num_reads = 0; > + > + loop { > + if let Some(ret) = cond() { > + return Ok(ret); > + } > + > + (|| { > + cur_time = with_bar!(bar, |b| self.read(b))?; > + > + /* Check if the timer is frozen for some reason. */ > + if cur_time == prev_time { > + if num_reads >= MAX_STALLED_READS { > + return Err(ETIMEDOUT); > + } > + num_reads += 1; > + } else { > + if cur_time >= deadline { > + return Err(ETIMEDOUT); > + } > + > + num_reads = 0; > + prev_time = cur_time; > + } > + > + Ok(()) > + })()?; > + } > + } > +} > > -- > 2.49.0 >