[PATCH v2 18/25] rust: io: make IoMem and ExclusiveIoMem lifetime-parameterized

[Danilo Krummrich <dakr@kernel.org>]

Add a lifetime parameter to IoMem<'bound, SIZE> and
ExclusiveIoMem<'bound, SIZE>, storing a &'bound Device<Bound> reference
to tie the mapping to the device's lifetime.

This mirrors the pci::Bar<'bound, SIZE> design and enables drivers to
hold I/O memory mappings directly in their HRT private data, tied to the
device lifetime.

IoRequest::iomap_* methods now return the mapping directly instead of
wrapping it in Devres. Callers that need device-managed revocation can
call the new into_devres() method.

Acked-by: Uwe Kleine-König <ukleinek@kernel.org>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 drivers/gpu/drm/tyr/driver.rs |   4 +-
 drivers/pwm/pwm_th1520.rs     |   4 +-
 rust/kernel/io/mem.rs         | 115 +++++++++++++++++-----------------
 3 files changed, 62 insertions(+), 61 deletions(-)

diff --git a/drivers/gpu/drm/tyr/driver.rs b/drivers/gpu/drm/tyr/driver.rs
index 96d83605e4b9..295a627de2b2 100644
--- a/drivers/gpu/drm/tyr/driver.rs
+++ b/drivers/gpu/drm/tyr/driver.rs
@@ -37,7 +37,7 @@
     regs, //
 };
 
-pub(crate) type IoMem = kernel::io::mem::IoMem<SZ_2M>;
+pub(crate) type IoMem = kernel::io::mem::IoMem<'static, SZ_2M>;
 
 pub(crate) struct TyrDrmDriver;
 
@@ -109,7 +109,7 @@ fn probe(
         let sram_regulator = Regulator::<regulator::Enabled>::get(pdev.as_ref(), c"sram")?;
 
         let request = pdev.io_request_by_index(0).ok_or(ENODEV)?;
-        let iomem = Arc::pin_init(request.iomap_sized::<SZ_2M>(), GFP_KERNEL)?;
+        let iomem = Arc::new(request.iomap_sized::<SZ_2M>()?.into_devres()?, GFP_KERNEL)?;
 
         issue_soft_reset(pdev.as_ref(), &iomem)?;
         gpu::l2_power_on(pdev.as_ref(), &iomem)?;
diff --git a/drivers/pwm/pwm_th1520.rs b/drivers/pwm/pwm_th1520.rs
index a7831b4ebe00..3deb39d8e0fc 100644
--- a/drivers/pwm/pwm_th1520.rs
+++ b/drivers/pwm/pwm_th1520.rs
@@ -92,7 +92,7 @@ struct Th1520WfHw {
 #[pin_data(PinnedDrop)]
 struct Th1520PwmDriverData {
     #[pin]
-    iomem: devres::Devres<IoMem<TH1520_PWM_REG_SIZE>>,
+    iomem: devres::Devres<IoMem<'static, TH1520_PWM_REG_SIZE>>,
     clk: Clk,
 }
 
@@ -351,7 +351,7 @@ fn probe(
             dev,
             TH1520_MAX_PWM_NUM,
             try_pin_init!(Th1520PwmDriverData {
-                iomem <- request.iomap_sized::<TH1520_PWM_REG_SIZE>(),
+                iomem <- request.iomap_sized::<TH1520_PWM_REG_SIZE>()?.into_devres(),
                 clk <- clk,
             }),
         )?;
diff --git a/rust/kernel/io/mem.rs b/rust/kernel/io/mem.rs
index fd5292df5870..a4cb12ee70d3 100644
--- a/rust/kernel/io/mem.rs
+++ b/rust/kernel/io/mem.rs
@@ -23,19 +23,19 @@
 };
 
 /// An IO request for a specific device and resource.
-pub struct IoRequest<'a> {
-    device: &'a Device<Bound>,
-    resource: &'a Resource,
+pub struct IoRequest<'bound> {
+    device: &'bound Device<Bound>,
+    resource: &'bound Resource,
 }
 
-impl<'a> IoRequest<'a> {
+impl<'bound> IoRequest<'bound> {
     /// Creates a new [`IoRequest`] instance.
     ///
     /// # Safety
     ///
     /// Callers must ensure that `resource` is valid for `device` during the
-    /// lifetime `'a`.
-    pub(crate) unsafe fn new(device: &'a Device<Bound>, resource: &'a Resource) -> Self {
+    /// lifetime `'bound`.
+    pub(crate) unsafe fn new(device: &'bound Device<Bound>, resource: &'bound Resource) -> Self {
         IoRequest { device, resource }
     }
 
@@ -73,22 +73,19 @@ pub(crate) unsafe fn new(device: &'a Device<Bound>, resource: &'a Resource) -> S
     ///       //
     ///       // No runtime checks will apply when reading and writing.
     ///       let request = pdev.io_request_by_index(0).ok_or(ENODEV)?;
-    ///       let iomem = request.iomap_sized::<42>();
-    ///       let iomem = KBox::pin_init(iomem, GFP_KERNEL)?;
-    ///
-    ///       let io = iomem.access(pdev.as_ref())?;
+    ///       let iomem = request.iomap_sized::<42>()?;
     ///
     ///       // Read and write a 32-bit value at `offset`.
-    ///       let data = io.read32(offset);
+    ///       let data = iomem.read32(offset);
     ///
-    ///       io.write32(data, offset);
+    ///       iomem.write32(data, offset);
     ///
     ///       # Ok(SampleDriver)
     ///     }
     /// }
     /// ```
-    pub fn iomap_sized<const SIZE: usize>(self) -> impl PinInit<Devres<IoMem<SIZE>>, Error> + 'a {
-        IoMem::new(self)
+    pub fn iomap_sized<const SIZE: usize>(self) -> Result<IoMem<'bound, SIZE>> {
+        IoMem::ioremap(self.device, self.resource)
     }
 
     /// Same as [`Self::iomap_sized`] but with exclusive access to the
@@ -97,10 +94,8 @@ pub fn iomap_sized<const SIZE: usize>(self) -> impl PinInit<Devres<IoMem<SIZE>>,
     /// This uses the [`ioremap()`] C API.
     ///
     /// [`ioremap()`]: https://docs.kernel.org/driver-api/device-io.html#getting-access-to-the-device
-    pub fn iomap_exclusive_sized<const SIZE: usize>(
-        self,
-    ) -> impl PinInit<Devres<ExclusiveIoMem<SIZE>>, Error> + 'a {
-        ExclusiveIoMem::new(self)
+    pub fn iomap_exclusive_sized<const SIZE: usize>(self) -> Result<ExclusiveIoMem<'bound, SIZE>> {
+        ExclusiveIoMem::ioremap(self.device, self.resource)
     }
 
     /// Maps an [`IoRequest`] where the size is not known at compile time,
@@ -138,27 +133,24 @@ pub fn iomap_exclusive_sized<const SIZE: usize>(
     ///       // family of functions should be used, leading to runtime checks on every
     ///       // access.
     ///       let request = pdev.io_request_by_index(0).ok_or(ENODEV)?;
-    ///       let iomem = request.iomap();
-    ///       let iomem = KBox::pin_init(iomem, GFP_KERNEL)?;
-    ///
-    ///       let io = iomem.access(pdev.as_ref())?;
+    ///       let iomem = request.iomap()?;
     ///
-    ///       let data = io.try_read32(offset)?;
+    ///       let data = iomem.try_read32(offset)?;
     ///
-    ///       io.try_write32(data, offset)?;
+    ///       iomem.try_write32(data, offset)?;
     ///
     ///       # Ok(SampleDriver)
     ///     }
     /// }
     /// ```
-    pub fn iomap(self) -> impl PinInit<Devres<IoMem<0>>, Error> + 'a {
-        Self::iomap_sized::<0>(self)
+    pub fn iomap(self) -> Result<IoMem<'bound>> {
+        self.iomap_sized::<0>()
     }
 
     /// Same as [`Self::iomap`] but with exclusive access to the underlying
     /// region.
-    pub fn iomap_exclusive(self) -> impl PinInit<Devres<ExclusiveIoMem<0>>, Error> + 'a {
-        Self::iomap_exclusive_sized::<0>(self)
+    pub fn iomap_exclusive(self) -> Result<ExclusiveIoMem<'bound, 0>> {
+        self.iomap_exclusive_sized::<0>()
     }
 }
 
@@ -167,9 +159,9 @@ pub fn iomap_exclusive(self) -> impl PinInit<Devres<ExclusiveIoMem<0>>, Error> +
 /// # Invariants
 ///
 /// - [`ExclusiveIoMem`] has exclusive access to the underlying [`IoMem`].
-pub struct ExclusiveIoMem<const SIZE: usize> {
+pub struct ExclusiveIoMem<'bound, const SIZE: usize> {
     /// The underlying `IoMem` instance.
-    iomem: IoMem<SIZE>,
+    iomem: IoMem<'bound, SIZE>,
 
     /// The region abstraction. This represents exclusive access to the
     /// range represented by the underlying `iomem`.
@@ -178,9 +170,9 @@ pub struct ExclusiveIoMem<const SIZE: usize> {
     _region: Region,
 }
 
-impl<const SIZE: usize> ExclusiveIoMem<SIZE> {
+impl<'bound, const SIZE: usize> ExclusiveIoMem<'bound, SIZE> {
     /// Creates a new `ExclusiveIoMem` instance.
-    fn ioremap(resource: &Resource) -> Result<Self> {
+    fn ioremap(dev: &'bound Device<Bound>, resource: &Resource) -> Result<Self> {
         let start = resource.start();
         let size = resource.size();
         let name = resource.name().unwrap_or_default();
@@ -194,26 +186,29 @@ fn ioremap(resource: &Resource) -> Result<Self> {
             )
             .ok_or(EBUSY)?;
 
-        let iomem = IoMem::ioremap(resource)?;
+        let iomem = IoMem::ioremap(dev, resource)?;
 
-        let iomem = ExclusiveIoMem {
+        Ok(ExclusiveIoMem {
             iomem,
             _region: region,
-        };
-
-        Ok(iomem)
+        })
     }
 
-    /// Creates a new `ExclusiveIoMem` instance from a previously acquired [`IoRequest`].
-    pub fn new<'a>(io_request: IoRequest<'a>) -> impl PinInit<Devres<Self>, Error> + 'a {
-        let dev = io_request.device;
-        let res = io_request.resource;
-
-        Devres::new(dev, Self::ioremap(res))
+    /// Consume the `ExclusiveIoMem` and register it as a device-managed resource.
+    ///
+    /// The returned `Devres<ExclusiveIoMem<'static, SIZE>>` can outlive the original lifetime
+    /// `'bound`. Access to the I/O memory is revoked when the device is unbound.
+    pub fn into_devres(self) -> Result<Devres<ExclusiveIoMem<'static, SIZE>>> {
+        // SAFETY: Casting to `'static` is sound because `Devres` guarantees the
+        // `ExclusiveIoMem` does not actually outlive the device -- access is revoked and the
+        // resource is released when the device is unbound.
+        let iomem: ExclusiveIoMem<'static, SIZE> = unsafe { core::mem::transmute(self) };
+        let dev = iomem.iomem.dev;
+        Devres::new(dev, iomem)
     }
 }
 
-impl<const SIZE: usize> Deref for ExclusiveIoMem<SIZE> {
+impl<const SIZE: usize> Deref for ExclusiveIoMem<'_, SIZE> {
     type Target = Mmio<SIZE>;
 
     fn deref(&self) -> &Self::Target {
@@ -230,12 +225,13 @@ fn deref(&self) -> &Self::Target {
 ///
 /// [`IoMem`] always holds an [`MmioRaw`] instance that holds a valid pointer to the
 /// start of the I/O memory mapped region.
-pub struct IoMem<const SIZE: usize = 0> {
+pub struct IoMem<'bound, const SIZE: usize = 0> {
+    dev: &'bound Device<Bound>,
     io: MmioRaw<SIZE>,
 }
 
-impl<const SIZE: usize> IoMem<SIZE> {
-    fn ioremap(resource: &Resource) -> Result<Self> {
+impl<'bound, const SIZE: usize> IoMem<'bound, SIZE> {
+    fn ioremap(dev: &'bound Device<Bound>, resource: &Resource) -> Result<Self> {
         // Note: Some ioremap() implementations use types that depend on the CPU
         // word width rather than the bus address width.
         //
@@ -267,28 +263,33 @@ fn ioremap(resource: &Resource) -> Result<Self> {
         }
 
         let io = MmioRaw::new(addr as usize, size)?;
-        let io = IoMem { io };
 
-        Ok(io)
+        Ok(IoMem { dev, io })
     }
 
-    /// Creates a new `IoMem` instance from a previously acquired [`IoRequest`].
-    pub fn new<'a>(io_request: IoRequest<'a>) -> impl PinInit<Devres<Self>, Error> + 'a {
-        let dev = io_request.device;
-        let res = io_request.resource;
-
-        Devres::new(dev, Self::ioremap(res))
+    /// Consume the `IoMem` and register it as a device-managed resource.
+    ///
+    /// The returned `Devres<IoMem<'static, SIZE>>` can outlive the original
+    /// lifetime `'bound`. Access to the I/O memory is revoked when the device
+    /// is unbound.
+    pub fn into_devres(self) -> Result<Devres<IoMem<'static, SIZE>>> {
+        // SAFETY: Casting to `'static` is sound because `Devres` guarantees the `IoMem` does not
+        // actually outlive the device -- access is revoked and the resource is released when the
+        // device is unbound.
+        let iomem: IoMem<'static, SIZE> = unsafe { core::mem::transmute(self) };
+        let dev = iomem.dev;
+        Devres::new(dev, iomem)
     }
 }
 
-impl<const SIZE: usize> Drop for IoMem<SIZE> {
+impl<const SIZE: usize> Drop for IoMem<'_, SIZE> {
     fn drop(&mut self) {
         // SAFETY: Safe as by the invariant of `Io`.
         unsafe { bindings::iounmap(self.io.addr() as *mut c_void) }
     }
 }
 
-impl<const SIZE: usize> Deref for IoMem<SIZE> {
+impl<const SIZE: usize> Deref for IoMem<'_, SIZE> {
     type Target = Mmio<SIZE>;
 
     fn deref(&self) -> &Self::Target {
-- 
2.54.0