[PATCH v2 06/12] rust/qdev: Refine the documentation for QDevProp trait

[Zhao Liu <zhao1.liu@intel.com>]

From: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>

Refine the documentation to clarify:
 * `unsfae` requires that `VALUE` must be valid.
 * using `*const` instead of `&` because the latter will cause compiler
   error.

Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
---
 rust/hw/core/src/qdev.rs | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/rust/hw/core/src/qdev.rs b/rust/hw/core/src/qdev.rs
index d8113238e513..89c21e7c6b50 100644
--- a/rust/hw/core/src/qdev.rs
+++ b/rust/hw/core/src/qdev.rs
@@ -109,9 +109,16 @@ pub trait ResettablePhasesImpl {
 ///
 /// # Safety
 ///
-/// This trait is marked as `unsafe` because currently having a `const` refer to
-/// an `extern static` as a reference instead of a raw pointer results in this
-/// compiler error:
+/// This trait is marked as `unsafe` because `VALUE` must be a valid raw
+/// reference to a [`bindings::PropertyInfo`].
+///
+/// Note we could not use a regular reference:
+///
+/// ```text
+/// const VALUE: &bindings::PropertyInfo = ...
+/// ```
+///
+/// because this results in the following compiler error:
 ///
 /// ```text
 /// constructing invalid value: encountered reference to `extern` static in `const`
@@ -119,7 +126,7 @@ pub trait ResettablePhasesImpl {
 ///
 /// This is because the compiler generally might dereference a normal reference
 /// during const evaluation, but not in this case (if it did, it'd need to
-/// dereference the raw pointer so this would fail to compile).
+/// dereference the raw pointer so using a `*const` would also fail to compile).
 ///
 /// It is the implementer's responsibility to provide a valid
 /// [`bindings::PropertyInfo`] pointer for the trait implementation to be safe.
-- 
2.34.1