[PATCH 10/16] gpu: nova-core: add basic timer device

Alexandre Courbot
2025-04-20T12:20:26Z

Add a timer that works with GPU time and provides the ability to wait on
a condition with a specific timeout.

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.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
---
drivers/gpu/nova-core/gpu.rs | 5 ++
drivers/gpu/nova-core/nova_core.rs | 1 +
drivers/gpu/nova-core/regs.rs | 10 +++
drivers/gpu/nova-core/timer.rs | 133 +++++++++++++++++++++++++++++++++++++
4 files changed, 149 insertions(+)

diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
index d43e710cc983d51f053dacbd77cbbfb79fa882c3..1b3e43e0412e2a2ea178c7404ea647c9e38d4e04 100644
--- a/drivers/gpu/nova-core/gpu.rs
+++ b/drivers/gpu/nova-core/gpu.rs
@@ -7,6 +7,7 @@
use crate::driver::Bar0;
use crate::firmware::Firmware;
use crate::regs;
+use crate::timer::Timer;
use crate::util;
use core::fmt;

@@ -153,6 +154,7 @@ pub(crate) struct Gpu {
bar: Devres<Bar0>,
fw: Firmware,
sysmem_flush: DmaObject,
+ timer: Timer,
}

#[pinned_drop]
@@ -217,11 +219,14 @@ pub(crate) fn new(
page
};

+ let timer = Timer::new();
+
Ok(pin_init!(Self {
spec,
bar,
fw,
sysmem_flush,
+ timer,
}))
}
}
diff --git a/drivers/gpu/nova-core/nova_core.rs b/drivers/gpu/nova-core/nova_core.rs
index 37c7eb0ea7a926bee4e3c661028847291bf07fa2..df3468c92c6081b3e2db218d92fbe1c40a0a75c3 100644
--- a/drivers/gpu/nova-core/nova_core.rs
+++ b/drivers/gpu/nova-core/nova_core.rs
@@ -26,6 +26,7 @@ macro_rules! with_bar {
mod firmware;
mod gpu;
mod regs;
+mod timer;
mod util;

kernel::module_pci_driver! {
diff --git a/drivers/gpu/nova-core/regs.rs b/drivers/gpu/nova-core/regs.rs
index 1e24787c4b5f432ac25fe399c8cb38b7350e44ae..f191cf4eb44c2b950e5cfcc6d04f95c122ce29d3 100644
--- a/drivers/gpu/nova-core/regs.rs
+++ b/drivers/gpu/nova-core/regs.rs
@@ -14,6 +14,16 @@
28:20 chipset => try_into Chipset, "chipset model"
);

+/* PTIMER */
+
+register!(PtimerTime0@0x00009400;
+ 31:0 lo => as u32, "low 32-bits of the timer"
+);
+
+register!(PtimerTime1@0x00009410;
+ 31:0 hi => as u32, "high 32 bits of the timer"
+);
+
/* PFB */

register!(PfbNisoFlushSysmemAddr@0x00100c10;
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)]
+
+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<Duration> 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()));
+ }
+ }
+ }
+
+ #[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<R, F: Fn() -> Option<R>>(
+ &self,
+ bar: &Devres<Bar0>,
+ timeout: Duration,
+ cond: F,
+ ) -> Result<R> {
+ // Number of consecutive time reads after which we consider the timer frozen if it hasn't
+ // moved forward.
+ const MAX_STALLED_READS: usize = 16;
+
+ 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