gpu: nova-core: register: redesign relative registers

The relative registers are currently very unsafe to use: callers can
specify any constant as the base address for access, meaning they can
effectively interpret any I/O address as any relative register.

Ideally, valid base addresses for a family of registers should be
explicitly defined in the code, and could only be used with the relevant
registers

This patch changes the relative register declaration from e.g.:

    register!(CPU_CTL @ +0x0000010, "CPU core control" {
        0:0     start as bool, "Start the CPU core";
    });

into:

    register!(CPU_CTL @ CpuCtlBase[0x10], "CPU core control" {
        0:0     start as bool, "Start the CPU core";
    });

Where `CpuCtlBase` is the name of a ZST used as a parameter of the
`RegisterBase<>` trait to define a trait unique to a class of register.
This specialized trait is then implemented for every type that provides
a valid base address, enabling said types to be passed as the base
address provider for the register's I/O accessor methods.

This design thus makes it impossible to pass an unexpected base address
to a relative register, and, since the valid bases are all known at
compile-time, also guarantees that all I/O accesses are done within the
valid bounds of the I/O range.

[acourbot@nvidia.com: add example in the commit log.]

Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://lore.kernel.org/r/20250718-nova-regs-v2-15-7b6a762aa1cd@nvidia.com
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>

3 files changed, 22 insertions, 13 deletions

diff --git a/drivers/gpu/nova-core/falcon/gsp.rs b/drivers/gpu/nova-core/falcon/gsp.rs
index d622e9a64470..0db9f94036a6 100644
--- a/drivers/gpu/nova-core/falcon/gsp.rs
+++ b/drivers/gpu/nova-core/falcon/gsp.rs
@@ -2,23 +2,27 @@
 
 use crate::{
     driver::Bar0,
-    falcon::{Falcon, FalconEngine},
-    regs,
+    falcon::{Falcon, FalconEngine, PFalconBase},
+    regs::{self, macros::RegisterBase},
 };
 
 /// Type specifying the `Gsp` falcon engine. Cannot be instantiated.
 pub(crate) struct Gsp(());
 
-impl FalconEngine for Gsp {
+impl RegisterBase<PFalconBase> for Gsp {
     const BASE: usize = 0x00110000;
 }
 
+impl FalconEngine for Gsp {
+    const ID: Self = Gsp(());
+}
+
 impl Falcon<Gsp> {
     /// Clears the SWGEN0 bit in the Falcon's IRQ status clear register to
     /// allow GSP to signal CPU for processing new messages in message queue.
     pub(crate) fn clear_swgen0_intr(&self, bar: &Bar0) {
         regs::NV_PFALCON_FALCON_IRQSCLR::default()
             .set_swgen0(true)
-            .write(bar, Gsp::BASE);
+            .write(bar, &Gsp::ID);
     }
 }
diff --git a/drivers/gpu/nova-core/falcon/hal/ga102.rs b/drivers/gpu/nova-core/falcon/hal/ga102.rs
index 52c33d3f22a8..3fdacd19322d 100644
--- a/drivers/gpu/nova-core/falcon/hal/ga102.rs
+++ b/drivers/gpu/nova-core/falcon/hal/ga102.rs
@@ -16,15 +16,15 @@ use crate::util;
 use super::FalconHal;
 
 fn select_core_ga102<E: FalconEngine>(bar: &Bar0) -> Result {
-    let bcr_ctrl = regs::NV_PRISCV_RISCV_BCR_CTRL::read(bar, E::BASE);
+    let bcr_ctrl = regs::NV_PRISCV_RISCV_BCR_CTRL::read(bar, &E::ID);
     if bcr_ctrl.core_select() != PeregrineCoreSelect::Falcon {
         regs::NV_PRISCV_RISCV_BCR_CTRL::default()
             .set_core_select(PeregrineCoreSelect::Falcon)
-            .write(bar, E::BASE);
+            .write(bar, &E::ID);
 
         // TIMEOUT: falcon core should take less than 10ms to report being enabled.
         util::wait_on(Delta::from_millis(10), || {
-            let r = regs::NV_PRISCV_RISCV_BCR_CTRL::read(bar, E::BASE);
+            let r = regs::NV_PRISCV_RISCV_BCR_CTRL::read(bar, &E::ID);
             if r.valid() {
                 Some(())
             } else {
@@ -76,16 +76,16 @@ fn signature_reg_fuse_version_ga102(
 fn program_brom_ga102<E: FalconEngine>(bar: &Bar0, params: &FalconBromParams) -> Result {
     regs::NV_PFALCON2_FALCON_BROM_PARAADDR::default()
         .set_value(params.pkc_data_offset)
-        .write(bar, E::BASE);
+        .write(bar, &E::ID);
     regs::NV_PFALCON2_FALCON_BROM_ENGIDMASK::default()
         .set_value(u32::from(params.engine_id_mask))
-        .write(bar, E::BASE);
+        .write(bar, &E::ID);
     regs::NV_PFALCON2_FALCON_BROM_CURR_UCODE_ID::default()
         .set_ucode_id(params.ucode_id)
-        .write(bar, E::BASE);
+        .write(bar, &E::ID);
     regs::NV_PFALCON2_FALCON_MOD_SEL::default()
         .set_algo(FalconModSelAlgo::Rsa3k)
-        .write(bar, E::BASE);
+        .write(bar, &E::ID);
 
     Ok(())
 }
diff --git a/drivers/gpu/nova-core/falcon/sec2.rs b/drivers/gpu/nova-core/falcon/sec2.rs
index 5147d9e2a7fe..dbc486a712ff 100644
--- a/drivers/gpu/nova-core/falcon/sec2.rs
+++ b/drivers/gpu/nova-core/falcon/sec2.rs
@@ -1,10 +1,15 @@
 // SPDX-License-Identifier: GPL-2.0
 
-use crate::falcon::FalconEngine;
+use crate::falcon::{FalconEngine, PFalconBase};
+use crate::regs::macros::RegisterBase;
 
 /// Type specifying the `Sec2` falcon engine. Cannot be instantiated.
 pub(crate) struct Sec2(());
 
-impl FalconEngine for Sec2 {
+impl RegisterBase<PFalconBase> for Sec2 {
     const BASE: usize = 0x00840000;
 }
+
+impl FalconEngine for Sec2 {
+    const ID: Self = Sec2(());
+}