uefi: fix clippy::as_ptr_cast_mut in gop

We can't use `as_mut_ptr()` as the underlying buffer
is only readable. As we know the operation
is only reading from the buffer, this is safe.

Author: phip1611

uefi-raw/src/protocol/console.rs

@@ -161,6 +161,8 @@ pub struct GraphicsOutputProtocol {
     pub set_mode: unsafe extern "efiapi" fn(*mut Self, mode_number: u32) -> Status,
     pub blt: unsafe extern "efiapi" fn(
         *mut Self,
+        // Depending on `blt_operation`, this is an IN parameter (readable)
+        // or an OUT parameter (writeable).
         blt_buffer: *mut GraphicsOutputBltPixel,
         blt_operation: GraphicsOutputBltOperation,
         source_x: usize,

uefi/src/proto/console/gop.rs

@@ -59,8 +59,8 @@ use core::fmt::{Debug, Formatter};
 use core::marker::PhantomData;
 use core::ptr::{self, NonNull};
 use uefi_raw::protocol::console::{
-    GraphicsOutputBltOperation, GraphicsOutputModeInformation, GraphicsOutputProtocol,
-    GraphicsOutputProtocolMode,
+    GraphicsOutputBltOperation, GraphicsOutputBltPixel, GraphicsOutputModeInformation,
+    GraphicsOutputProtocol, GraphicsOutputProtocolMode,
 };
 
 pub use uefi_raw::protocol::console::PixelBitmask;
@@ -201,7 +201,8 @@ impl GraphicsOutput {
                     match src_region {
                         BltRegion::Full => (self.0.blt)(
                             &mut self.0,
-                            buffer.as_ptr() as *mut _,
+                            // SAFETY: The buffer is only used for reading.
+                            buffer.as_ptr().cast::<GraphicsOutputBltPixel>().cast_mut(),
                             GraphicsOutputBltOperation::BLT_BUFFER_TO_VIDEO,
                             0,
                             0,
@@ -217,7 +218,8 @@ impl GraphicsOutput {
                             px_stride,
                         } => (self.0.blt)(
                             &mut self.0,
-                            buffer.as_ptr() as *mut _,
+                            // SAFETY: The buffer is only used for reading.
+                            buffer.as_ptr().cast::<GraphicsOutputBltPixel>().cast_mut(),
                             GraphicsOutputBltOperation::BLT_BUFFER_TO_VIDEO,
                             src_x,
                             src_y,