[PATCH v7 20/23] 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    | 13 +++++++++-
 drivers/gpu/nova-core/gsp/fw/commands.rs | 30 ++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/nova-core/gsp/commands.rs b/drivers/gpu/nova-core/gsp/commands.rs
index bf9e3086565f..44f8b08683f9 100644
--- a/drivers/gpu/nova-core/gsp/commands.rs
+++ b/drivers/gpu/nova-core/gsp/commands.rs
@@ -186,10 +186,13 @@ 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],
     bar1_pde_base: u64,
+    /// First usable FB region `(base, size)` for memory allocation.
+    #[expect(dead_code)]
+    usable_fb_region: Option<(u64, u64)>,
 }
 
 impl MessageFromGsp for GetGspStaticInfoReply {
@@ -204,6 +207,7 @@ fn read(
         Ok(GetGspStaticInfoReply {
             gpu_name: msg.gpu_name_str(),
             bar1_pde_base: msg.bar1_pde_base(),
+            usable_fb_region: msg.first_usable_fb_region(),
         })
     }
 }
@@ -235,6 +239,13 @@ pub(crate) fn gpu_name(&self) -> core::result::Result<&str, GpuNameError> {
     pub(crate) fn bar1_pde_base(&self) -> u64 {
         self.bar1_pde_base
     }
+
+    /// 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 f069f4092911..976eca5a59c4 100644
--- a/drivers/gpu/nova-core/gsp/fw/commands.rs
+++ b/drivers/gpu/nova-core/gsp/fw/commands.rs
@@ -122,6 +122,36 @@ impl GspStaticConfigInfo {
     pub(crate) fn bar1_pde_base(&self) -> u64 {
         self.0.bar1PdeBase
     }
+
+    /// 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 as usize {
+            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