gpu: nova-core: add FbHal::frts_size() for GA100 support

Introduce FbHal method frts_size() to return the size of the FRTS
window.  GA100 is a special case in that although there is an
FRTS, its size must arbitrarily be set to 0.

Note that we cannot use supports_display() to determine the FRTS
size because there are other GPUs (e.g. GA102GL) that have display
disabled (and so supports_display() returns False), but the FRTS
window size still needs to be 1MB.

Signed-off-by: Timur Tabi <ttabi@nvidia.com>
Reviewed-by: Eliot Courtney <ecourtney@nvidia.com>
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260417191359.1307434-5-ttabi@nvidia.com
[acourbot: apply requested fix to commit message.]
[acourbot: fix minor conflict.]
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>

drivers/gpu/nova-core/fb.rs

@@ -213,10 +213,10 @@ pub(crate) fn new(chipset: Chipset, bar: &Bar0, gsp_fw: &GspFirmware) -> Result<
 
         let frts = {
             const FRTS_DOWN_ALIGN: Alignment = Alignment::new::<SZ_128K>();
-            const FRTS_SIZE: u64 = u64::SZ_1M;
-            let frts_base = vga_workspace.start.align_down(FRTS_DOWN_ALIGN) - FRTS_SIZE;
+            let frts_size: u64 = hal.frts_size();
+            let frts_base = vga_workspace.start.align_down(FRTS_DOWN_ALIGN) - frts_size;
 
-            FbRange(frts_base..frts_base + FRTS_SIZE)
+            FbRange(frts_base..frts_base + frts_size)
         };
 
         let boot = {

drivers/gpu/nova-core/fb/hal.rs

@@ -25,6 +25,9 @@ pub(crate) trait FbHal {
 
     /// Returns the VRAM size, in bytes.
     fn vidmem_size(&self, bar: &Bar0) -> u64;
+
+    /// Returns the FRTS size, in bytes.
+    fn frts_size(&self) -> u64;
 }
 
 /// Returns the HAL corresponding to `chipset`.

drivers/gpu/nova-core/fb/hal/ga100.rs

@@ -66,6 +66,12 @@ fn supports_display(&self, bar: &Bar0) -> bool {
     fn vidmem_size(&self, bar: &Bar0) -> u64 {
         super::tu102::vidmem_size_gp102(bar)
     }
+
+    // GA100 is a special case where its FRTS region exists, but is empty.  We
+    // return a size of 0 because we still need to record where the region starts.
+    fn frts_size(&self) -> u64 {
+        0
+    }
 }
 
 const GA100: Ga100 = Ga100;

drivers/gpu/nova-core/fb/hal/ga102.rs

@@ -35,6 +35,10 @@ fn supports_display(&self, bar: &Bar0) -> bool {
     fn vidmem_size(&self, bar: &Bar0) -> u64 {
         vidmem_size_ga102(bar)
     }
+
+    fn frts_size(&self) -> u64 {
+        super::tu102::frts_size_tu102()
+    }
 }
 
 const GA102: Ga102 = Ga102;

drivers/gpu/nova-core/fb/hal/tu102.rs

@@ -2,7 +2,8 @@
 
 use kernel::{
     io::Io,
-    prelude::*, //
+    prelude::*,
+    sizes::*, //
 };
 
 use crate::{
@@ -38,6 +39,10 @@ pub(super) fn vidmem_size_gp102(bar: &Bar0) -> u64 {
         .usable_fb_size()
 }
 
+pub(super) const fn frts_size_tu102() -> u64 {
+    u64::SZ_1M
+}
+
 struct Tu102;
 
 impl FbHal for Tu102 {
@@ -56,6 +61,10 @@ fn supports_display(&self, bar: &Bar0) -> bool {
     fn vidmem_size(&self, bar: &Bar0) -> u64 {
         vidmem_size_gp102(bar)
     }
+
+    fn frts_size(&self) -> u64 {
+        frts_size_tu102()
+    }
 }
 
 const TU102: Tu102 = Tu102;