[PATCH v8 04/25] 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 via
usable_fb_region() API 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    | 12 ++++++++-
 drivers/gpu/nova-core/gsp/fw/commands.rs | 32 ++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/nova-core/gsp/commands.rs b/drivers/gpu/nova-core/gsp/commands.rs
index 8f270eca33be..c31046df3acf 100644
--- a/drivers/gpu/nova-core/gsp/commands.rs
+++ b/drivers/gpu/nova-core/gsp/commands.rs
@@ -186,9 +186,11 @@ 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],
+    /// First usable FB region `(base, size)` for memory allocation.
+    usable_fb_region: Option<(u64, u64)>,
 }
 
 impl MessageFromGsp for GetGspStaticInfoReply {
@@ -202,6 +204,7 @@ fn read(
     ) -> Result<Self, Self::InitError> {
         Ok(GetGspStaticInfoReply {
             gpu_name: msg.gpu_name_str(),
+            usable_fb_region: msg.first_usable_fb_region(),
         })
     }
 }
@@ -228,6 +231,13 @@ pub(crate) fn gpu_name(&self) -> core::result::Result<&str, GpuNameError> {
             .to_str()
             .map_err(GpuNameError::InvalidUtf8)
     }
+
+    /// Returns the usable FB region `(base, size)` for driver allocation which is
+    /// already retrieved from the GSP.
+    #[expect(dead_code)]
+    pub(crate) fn usable_fb_region(&self) -> Option<(u64, u64)> {
+        self.usable_fb_region
+    }
 }
 
 /// Send the [`GetGspInfo`] command and awaits for its reply.
diff --git a/drivers/gpu/nova-core/gsp/fw/commands.rs b/drivers/gpu/nova-core/gsp/fw/commands.rs
index 21be44199693..ff771a4aba4f 100644
--- a/drivers/gpu/nova-core/gsp/fw/commands.rs
+++ b/drivers/gpu/nova-core/gsp/fw/commands.rs
@@ -5,6 +5,7 @@
 use kernel::{device, pci};
 
 use crate::gsp::GSP_PAGE_SIZE;
+use crate::num::IntoSafeCast;
 
 use super::bindings;
 
@@ -114,6 +115,37 @@ impl GspStaticConfigInfo {
     pub(crate) fn gpu_name_str(&self) -> [u8; 64] {
         self.0.gpuNameString
     }
+
+    /// Extract 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).
+    pub(crate) fn first_usable_fb_region(&self) -> Option<(u64, u64)> {
+        let fb_info = &self.0.fbRegionInfoParams;
+        for i in 0..fb_info.numFBRegions.into_safe_cast() {
+            if let Some(reg) = fb_info.fbRegion.get(i) {
+                // Skip malformed regions where limit < base.
+                if reg.limit < reg.base {
+                    continue;
+                }
+
+                // 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;
+                    return Some((reg.base, size));
+                }
+            }
+        }
+        None
+    }
 }
 
 // SAFETY: Padding is explicit and will not contain uninitialized data.
-- 
2.34.1