[PATCH v10 02/21] gpu: nova-core: gsp: Extract usable FB region from GSP

[Joel Fernandes <joelagnelf@nvidia.com>]

Add first_usable_fb_region() to GspStaticConfigInfo to extract the first
usable FB region from GSP's fbRegionInfoParams. Usable regions are those
that are not reserved or protected.

The extracted region is stored in GetGspStaticInfoReply and exposed as
usable_fb_region field for use by the memory subsystem.

Cc: Nikola Djukic <ndjukic@nvidia.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
---
 drivers/gpu/nova-core/gsp/commands.rs    | 11 ++++--
 drivers/gpu/nova-core/gsp/fw/commands.rs | 44 +++++++++++++++++++++++-
 2 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/nova-core/gsp/commands.rs b/drivers/gpu/nova-core/gsp/commands.rs
index c89c7b57a751..41742c1633c8 100644
--- a/drivers/gpu/nova-core/gsp/commands.rs
+++ b/drivers/gpu/nova-core/gsp/commands.rs
@@ -4,6 +4,7 @@
     array,
     convert::Infallible,
     ffi::FromBytesUntilNulError,
+    ops::Range,
     str::Utf8Error, //
 };
 
@@ -189,22 +190,28 @@ fn init(&self) -> impl Init<Self::Command, Self::InitError> {
     }
 }
 
-/// The reply from the GSP to the [`GetGspInfo`] command.
+/// The reply from the GSP to the [`GetGspStaticInfo`] command.
 pub(crate) struct GetGspStaticInfoReply {
     gpu_name: [u8; 64],
+    /// Usable FB (VRAM) region for driver memory allocation.
+    #[expect(dead_code)]
+    pub(crate) usable_fb_region: Range<u64>,
 }
 
 impl MessageFromGsp for GetGspStaticInfoReply {
     const FUNCTION: MsgFunction = MsgFunction::GetGspStaticInfo;
     type Message = GspStaticConfigInfo;
-    type InitError = Infallible;
+    type InitError = Error;
 
     fn read(
         msg: &Self::Message,
         _sbuffer: &mut SBufferIter<array::IntoIter<&[u8], 2>>,
     ) -> Result<Self, Self::InitError> {
+        let (base, size) = msg.first_usable_fb_region().ok_or(ENODEV)?;
+
         Ok(GetGspStaticInfoReply {
             gpu_name: msg.gpu_name_str(),
+            usable_fb_region: base..base.saturating_add(size),
         })
     }
 }
diff --git a/drivers/gpu/nova-core/gsp/fw/commands.rs b/drivers/gpu/nova-core/gsp/fw/commands.rs
index db46276430be..9fffa74d03f9 100644
--- a/drivers/gpu/nova-core/gsp/fw/commands.rs
+++ b/drivers/gpu/nova-core/gsp/fw/commands.rs
@@ -10,7 +10,10 @@
     }, //
 };
 
-use crate::gsp::GSP_PAGE_SIZE;
+use crate::{
+    gsp::GSP_PAGE_SIZE,
+    num::IntoSafeCast, //
+};
 
 use super::bindings;
 
@@ -121,6 +124,45 @@ impl GspStaticConfigInfo {
     pub(crate) fn gpu_name_str(&self) -> [u8; 64] {
         self.0.gpuNameString
     }
+
+    /// Returns an iterator over valid FB regions from GSP firmware data.
+    fn fb_regions(
+        &self,
+    ) -> impl Iterator<Item = &bindings::NV2080_CTRL_CMD_FB_GET_FB_REGION_FB_REGION_INFO> {
+        let fb_info = &self.0.fbRegionInfoParams;
+        fb_info
+            .fbRegion
+            .iter()
+            .take(fb_info.numFBRegions.into_safe_cast())
+            .filter(|reg| reg.limit >= reg.base)
+    }
+
+    /// Extracts the first usable FB region from GSP firmware data.
+    ///
+    /// Returns the first region suitable for driver memory allocation as a `(base, size)` tuple.
+    /// Usable regions are those that:
+    /// - Are not reserved for firmware internal use.
+    /// - Are not protected (hardware-enforced access restrictions).
+    /// - Support compression (can use GPU memory compression for bandwidth).
+    /// - Support ISO (isochronous memory for display requiring guaranteed bandwidth).
+    ///
+    /// TODO: Multiple discontinuous usable regions of RAM are possible in
+    /// special cases. We need to support it (to also match Nouveau's behavior).
+    pub(crate) fn first_usable_fb_region(&self) -> Option<(u64, u64)> {
+        self.fb_regions().find_map(|reg| {
+            // Filter: not reserved, not protected, supports compression and ISO.
+            if reg.reserved == 0
+                && reg.bProtected == 0
+                && reg.supportCompressed != 0
+                && reg.supportISO != 0
+            {
+                let size = reg.limit - reg.base + 1;
+                Some((reg.base, size))
+            } else {
+                None
+            }
+        })
+    }
 }
 
 // SAFETY: Padding is explicit and will not contain uninitialized data.
-- 
2.34.1