[PATCH v1] drm/tyr: make SRAM supply optional like panthor

["Onur Özkan" <work@onurozkan.dev>]

On rk3588s, `dmesg | grep 'tyr'` logs:

  tyr fb000000.gpu: supply SRAM not found, using dummy regulator

This happens because Tyr calls Regulator<Enabled>::get() for SRAM,
which goes through the non-optional regulator_get() path. If the
device tree doesn't provide sram-supply, regulator core falls back
to a dummy regulator and writes that log.

Panthor handles SRAM as optional and tolerates missing sram-supply.
This patch matches that behavior in Tyr by using optional regulator
lookup and storing SRAM as Option<Regulator<Enabled>> which avoids
dummy-regulator fallback/noise when SRAM is not described inside
the device tree.

Link: https://rust-for-linux.zulipchat.com/#narrow/stream/x/topic/x/near/573210018
Signed-off-by: Onur Özkan <work@onurozkan.dev>
---
 drivers/gpu/drm/tyr/driver.rs |  5 +++--
 rust/kernel/regulator.rs      | 40 +++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/tyr/driver.rs b/drivers/gpu/drm/tyr/driver.rs
index 0389c558c036..e0856deb83ec 100644
--- a/drivers/gpu/drm/tyr/driver.rs
+++ b/drivers/gpu/drm/tyr/driver.rs
@@ -113,7 +113,8 @@ fn probe(
         coregroup_clk.prepare_enable()?;
 
         let mali_regulator = Regulator::<regulator::Enabled>::get(pdev.as_ref(), c_str!("mali"))?;
-        let sram_regulator = Regulator::<regulator::Enabled>::get(pdev.as_ref(), c_str!("sram"))?;
+        let sram_regulator =
+            Regulator::<regulator::Enabled>::get_optional(pdev.as_ref(), c_str!("sram"))?;
 
         let request = pdev.io_request_by_index(0).ok_or(ENODEV)?;
         let iomem = Arc::pin_init(request.iomap_sized::<SZ_2M>(), GFP_KERNEL)?;
@@ -201,5 +202,5 @@ struct Clocks {
 #[pin_data]
 struct Regulators {
     mali: Regulator<regulator::Enabled>,
-    sram: Regulator<regulator::Enabled>,
+    sram: Option<Regulator<regulator::Enabled>>,
 }
diff --git a/rust/kernel/regulator.rs b/rust/kernel/regulator.rs
index 2c44827ad0b7..8d95e5e80051 100644
--- a/rust/kernel/regulator.rs
+++ b/rust/kernel/regulator.rs
@@ -283,6 +283,29 @@ fn get_internal(dev: &Device, name: &CStr) -> Result<Regulator<T>> {
         })
     }
 
+    fn get_optional_internal(dev: &Device, name: &CStr) -> Result<Option<Regulator<T>>> {
+        // SAFETY: It is safe to call `regulator_get_optional()`, on a
+        // device pointer received from the C code.
+        let inner = from_err_ptr(unsafe {
+            bindings::regulator_get_optional(dev.as_raw(), name.as_char_ptr())
+        });
+
+        let inner = match inner {
+            Ok(inner) => inner,
+            Err(ENODEV) => return Ok(None),
+            Err(err) => return Err(err),
+        };
+
+        // SAFETY: We can safely trust `inner` to be a pointer to a valid
+        // regulator if `ERR_PTR` was not returned.
+        let inner = unsafe { NonNull::new_unchecked(inner) };
+
+        Ok(Some(Self {
+            inner,
+            _phantom: PhantomData,
+        }))
+    }
+
     fn enable_internal(&self) -> Result {
         // SAFETY: Safe as per the type invariants of `Regulator`.
         to_result(unsafe { bindings::regulator_enable(self.inner.as_ptr()) })
@@ -300,6 +323,11 @@ pub fn get(dev: &Device, name: &CStr) -> Result<Self> {
         Regulator::get_internal(dev, name)
     }
 
+    /// Obtains an optional [`Regulator`] instance from the system.
+    pub fn get_optional(dev: &Device, name: &CStr) -> Result<Option<Self>> {
+        Regulator::get_optional_internal(dev, name)
+    }
+
     /// Attempts to convert the regulator to an enabled state.
     pub fn try_into_enabled(self) -> Result<Regulator<Enabled>, Error<Disabled>> {
         // We will be transferring the ownership of our `regulator_get()` count to
@@ -329,6 +357,18 @@ pub fn get(dev: &Device, name: &CStr) -> Result<Self> {
             .map_err(|error| error.error)
     }
 
+    /// Obtains an optional [`Regulator`] instance from the system and enables it.
+    pub fn get_optional(dev: &Device, name: &CStr) -> Result<Option<Self>> {
+        match Regulator::<Disabled>::get_optional_internal(dev, name)? {
+            Some(regulator) => {
+                let enabled_regulator =
+                    regulator.try_into_enabled().map_err(|error| error.error)?;
+                Ok(Some(enabled_regulator))
+            }
+            None => Ok(None),
+        }
+    }
+
     /// Attempts to convert the regulator to a disabled state.
     pub fn try_into_disabled(self) -> Result<Regulator<Disabled>, Error<Enabled>> {
         // We will be transferring the ownership of our `regulator_get()` count
-- 
2.51.2