Add minimal platform driver for bcm2835-rng

Implements the bare minimum for a platform driver to register
itself with the core. It won't be able to do anything, except
show up in sysfs.

Signed-off-by: Sven Van Asbroeck <thesven73@gmail.com>

drivers/char/hw_random/Kconfig

@@ -98,6 +98,19 @@ config HW_RANDOM_BCM2835
 
 	  If unsure, say Y.
 
+config HW_RANDOM_BCM2835_RUST
+	tristate "Rust implementation of Broadcom BCM2835 Random Number Generator"
+	depends on HAS_RUST && ARCH_BCM2835
+	help
+	  This driver provides alternative Rust-based kernel-side support
+	  for the Random Number Generator hardware found on the Broadcom
+	  BCM2835 SoC.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called bcm2835_rng_rust
+
+	  If unsure, say N.
+
 config HW_RANDOM_IPROC_RNG200
 	tristate "Broadcom iProc/STB RNG200 support"
 	depends on ARCH_BCM_IPROC || ARCH_BCM2835 || ARCH_BRCMSTB

drivers/char/hw_random/Makefile

@@ -31,6 +31,7 @@ obj-$(CONFIG_HW_RANDOM_PSERIES) += pseries-rng.o
 obj-$(CONFIG_HW_RANDOM_POWERNV) += powernv-rng.o
 obj-$(CONFIG_HW_RANDOM_HISI)	+= hisi-rng.o
 obj-$(CONFIG_HW_RANDOM_BCM2835) += bcm2835-rng.o
+obj-$(CONFIG_HW_RANDOM_BCM2835_RUST) += bcm2835_rng_rust.o
 obj-$(CONFIG_HW_RANDOM_IPROC_RNG200) += iproc-rng200.o
 obj-$(CONFIG_HW_RANDOM_ST) += st-rng.o
 obj-$(CONFIG_HW_RANDOM_XGENE) += xgene-rng.o

drivers/char/hw_random/bcm2835_rng_rust.rs

@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Broadcom BCM2835 Random Number Generator support.
+
+#![no_std]
+#![feature(allocator_api, global_asm)]
+
+use alloc::boxed::Box;
+use core::pin::Pin;
+use kernel::prelude::*;
+use kernel::{cstr, platdev};
+
+module! {
+    type: RngModule,
+    name: b"bcm2835_rng_rust",
+    author: b"Rust for Linux Contributors",
+    description: b"BCM2835 Random Number Generator (RNG) driver",
+    license: b"GPL v2",
+}
+
+struct RngModule {
+    _pdev: Pin<Box<platdev::Registration>>,
+}
+
+impl KernelModule for RngModule {
+    fn init() -> Result<Self> {
+        let pdev = platdev::Registration::new_pinned(cstr!("bcm2835-rng-rust"), &THIS_MODULE)?;
+
+        Ok(RngModule { _pdev: pdev })
+    }
+}