[PATCH RFC v2 4/5] gpu: nova-core: add basic timer device

[Alexandre Courbot <acourbot@nvidia.com>]

Add a basic timer device and exercise it during device probing. This
first draft is probably very questionable.

One point in particular which should IMHO receive attention: the generic
wait_on() method aims at providing similar functionality to Nouveau's
nvkm_[num]sec() macros. Since this method will be heavily used with
different conditions to test, I'd like to avoid monomorphizing it
entirely with each instance ; that's something that is achieved in
nvkm_xsec() using functions that the macros invoke.

I have tried achieving the same result in Rust using closures (kept
as-is in the current code), but they seem to be monomorphized as well.
Calling extra functions could work better, but looks also less elegant
to me, so I am really open to suggestions here.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
---
 drivers/gpu/nova-core/driver.rs    |   4 +-
 drivers/gpu/nova-core/gpu.rs       |  58 ++++++++++++++++-
 drivers/gpu/nova-core/nova_core.rs |   1 +
 drivers/gpu/nova-core/regs.rs      |   8 +++
 drivers/gpu/nova-core/timer.rs     | 124 +++++++++++++++++++++++++++++++++++++
 5 files changed, 193 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/nova-core/driver.rs b/drivers/gpu/nova-core/driver.rs
index 63c19f140fbdd65d8fccf81669ac590807cc120f..0cd23aa306e4082405f480afc0530a41131485e7 100644
--- a/drivers/gpu/nova-core/driver.rs
+++ b/drivers/gpu/nova-core/driver.rs
@@ -10,7 +10,7 @@ pub(crate) struct NovaCore {
     pub(crate) gpu: Gpu,
 }
 
-const BAR0_SIZE: usize = 8;
+const BAR0_SIZE: usize = 0x9500;
 pub(crate) type Bar0 = pci::Bar<BAR0_SIZE>;
 
 kernel::pci_device_table!(
@@ -42,6 +42,8 @@ fn probe(pdev: &mut pci::Device, _info: &Self::IdInfo) -> Result<Pin<KBox<Self>>
             GFP_KERNEL,
         )?;
 
+        let _ = this.gpu.test_timer();
+
         Ok(this)
     }
 }
diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
index 58b97c7f0b2ab1edacada8346b139f6336b68272..8fa8616c0deccc7297b090fcbe74f3cda5cc9741 100644
--- a/drivers/gpu/nova-core/gpu.rs
+++ b/drivers/gpu/nova-core/gpu.rs
@@ -1,12 +1,16 @@
 // SPDX-License-Identifier: GPL-2.0
 
+use kernel::device::Device;
+use kernel::types::ARef;
 use kernel::{
     device, devres::Devres, error::code::*, firmware, fmt, pci, prelude::*, str::BStr, str::CString,
 };
 
 use crate::driver::Bar0;
 use crate::regs;
+use crate::timer::Timer;
 use core::fmt;
+use core::time::Duration;
 
 const fn to_lowercase_bytes<const N: usize>(s: &str) -> [u8; N] {
     let src = s.as_bytes();
@@ -201,10 +205,12 @@ fn new(dev: &device::Device, spec: &Spec, ver: &str) -> Result<Firmware> {
 /// Structure holding the resources required to operate the GPU.
 #[pin_data]
 pub(crate) struct Gpu {
+    dev: ARef<Device>,
     spec: Spec,
     /// MMIO mapping of PCI BAR 0
     bar: Devres<Bar0>,
     fw: Firmware,
+    timer: Timer,
 }
 
 impl Gpu {
@@ -220,6 +226,56 @@ pub(crate) fn new(pdev: &pci::Device, bar: Devres<Bar0>) -> Result<impl PinInit<
             spec.revision
         );
 
-        Ok(pin_init!(Self { spec, bar, fw }))
+        let dev = pdev.as_ref().into();
+        let timer = Timer::new();
+
+        Ok(pin_init!(Self {
+            dev,
+            spec,
+            bar,
+            fw,
+            timer,
+        }))
+    }
+
+    pub(crate) fn test_timer(&self) -> Result<()> {
+        let bar = self.bar.try_access().ok_or(ENXIO)?;
+        dev_info!(&self.dev, "testing timer subdev\n");
+        dev_info!(&self.dev, "current timestamp: {}\n", self.timer.read(&bar));
+        drop(bar);
+
+        assert!(matches!(
+            self.timer
+                .wait_on(&self.bar, Duration::from_millis(10), || Some(())),
+            Ok(())
+        ));
+
+        let bar = self.bar.try_access().ok_or(ENXIO)?;
+        dev_info!(
+            &self.dev,
+            "timestamp after immediate exit: {}\n",
+            self.timer.read(&bar)
+        );
+        let t1 = self.timer.read(&bar);
+        drop(bar);
+
+        assert_eq!(
+            self.timer
+                .wait_on(&self.bar, Duration::from_millis(10), || Option::<()>::None),
+            Err(ETIMEDOUT)
+        );
+
+        let bar = self.bar.try_access().ok_or(ENXIO)?;
+        let t2 = self.timer.read(&bar);
+        assert!(t2 - t1 >= Duration::from_millis(10));
+        dev_info!(
+            &self.dev,
+            "timestamp after timeout: {} ({:?})\n",
+            self.timer.read(&bar),
+            t2 - t1
+        );
+        drop(bar);
+
+        Ok(())
     }
 }
diff --git a/drivers/gpu/nova-core/nova_core.rs b/drivers/gpu/nova-core/nova_core.rs
index 8479be2a3f31798e887228863f223d42a63bd8ca..891a93ba7656d2aa5e1fa4357d1d84ee3a054942 100644
--- a/drivers/gpu/nova-core/nova_core.rs
+++ b/drivers/gpu/nova-core/nova_core.rs
@@ -6,6 +6,7 @@
 mod firmware;
 mod gpu;
 mod regs;
+mod timer;
 
 kernel::module_pci_driver! {
     type: driver::NovaCore,
diff --git a/drivers/gpu/nova-core/regs.rs b/drivers/gpu/nova-core/regs.rs
index a874cb2fa5bedee258a60e5c3b471f52e5f82469..35bbd3c0b58972de3a2478ef20f93f31c69940e7 100644
--- a/drivers/gpu/nova-core/regs.rs
+++ b/drivers/gpu/nova-core/regs.rs
@@ -172,3 +172,11 @@ impl Builder<$name> {
     7:4     major_rev as (u8), "major revision of the chip";
     25:20   chipset try_into (Chipset), "chipset model"
 );
+
+nv_reg!(PtimerTime0@0x00009400;
+    31:0    lo as (u32), "low 32-bits of the timer"
+);
+
+nv_reg!(PtimerTime1@0x00009410;
+    31:0    hi as (u32), "high 32 bits of the timer"
+);
diff --git a/drivers/gpu/nova-core/timer.rs b/drivers/gpu/nova-core/timer.rs
new file mode 100644
index 0000000000000000000000000000000000000000..919995bf32141c568206fda165dcac6f4d4ce8b8
--- /dev/null
+++ b/drivers/gpu/nova-core/timer.rs
@@ -0,0 +1,124 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Nova Core Timer subdevice
+
+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`].
+///
+/// TODO: add Kunit tests!
+#[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<u64> for Timestamp {
+    type Output = Self;
+
+    fn add(self, rhs: u64) -> Self::Output {
+        Timestamp(self.0.wrapping_add(rhs))
+    }
+}
+
+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::new().hi(time.upper_32_bits()).write(bar);
+        regs::PtimerTime0::new().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,
+        dev_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 bar = dev_bar.try_access().ok_or(ENXIO)?;
+            let cur_time = self.read(&bar);
+            let deadline = cur_time + u64::try_from(timeout.as_nanos()).unwrap_or(u64::MAX);
+
+            (cur_time, cur_time, deadline)
+        };
+        let mut num_reads = 0;
+
+        loop {
+            if let Some(ret) = cond() {
+                return Ok(ret);
+            }
+
+            (|| {
+                let bar = dev_bar.try_access().ok_or(ENXIO)?;
+                cur_time = self.read(&bar);
+
+                /* 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(())
+            })()?;
+        }
+    }
+}

-- 
2.48.1