[PATCH v1 04/12] 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.

Reviewed-by: John Hubbard <jhubbard@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 | 42 +++++++++++++++++++++++-
 2 files changed, 49 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/nova-core/gsp/commands.rs b/drivers/gpu/nova-core/gsp/commands.rs
index c89c7b57a751..049fff337611 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, //
 };
 
@@ -189,15 +190,18 @@ 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,
@@ -205,6 +209,7 @@ fn read(
     ) -> Result<Self, Self::InitError> {
         Ok(GetGspStaticInfoReply {
             gpu_name: msg.gpu_name_str(),
+            usable_fb_region: msg.usable_fb_regions_iter().next().ok_or(ENODEV)?,
         })
     }
 }
@@ -233,7 +238,7 @@ pub(crate) fn gpu_name(&self) -> core::result::Result<&str, GpuNameError> {
     }
 }
 
-/// Send the [`GetGspInfo`] command and awaits for its reply.
+/// Send the [`GetGspStaticInfo`] command and awaits for its reply.
 pub(crate) fn get_gsp_info(cmdq: &Cmdq, bar: &Bar0) -> Result<GetGspStaticInfoReply> {
     cmdq.send_command(bar, GetGspStaticInfo)
 }
diff --git a/drivers/gpu/nova-core/gsp/fw/commands.rs b/drivers/gpu/nova-core/gsp/fw/commands.rs
index db46276430be..50b9c205566f 100644
--- a/drivers/gpu/nova-core/gsp/fw/commands.rs
+++ b/drivers/gpu/nova-core/gsp/fw/commands.rs
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
+use core::ops::Range;
+
 use kernel::{
     device,
     pci,
@@ -10,7 +12,10 @@
     }, //
 };
 
-use crate::gsp::GSP_PAGE_SIZE;
+use crate::{
+    gsp::GSP_PAGE_SIZE,
+    num::IntoSafeCast, //
+};
 
 use super::bindings;
 
@@ -121,6 +126,41 @@ 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)
+    }
+
+    /// Iterates over usable FB regions from GSP firmware data.
+    ///
+    /// Each yielded region is a [`Range<u64>`] suitable for driver memory allocation.
+    /// Usable regions are those that satisfy all the following properties:
+    /// - 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 usable_fb_regions_iter(&self) -> impl Iterator<Item = Range<u64>> + '_ {
+        self.fb_regions().filter_map(|reg| {
+            // Filter: not reserved, not protected, supports compression and ISO.
+            if reg.reserved == 0
+                && reg.bProtected == 0
+                && reg.supportCompressed != 0
+                && reg.supportISO != 0
+            {
+                reg.limit.checked_add(1).map(|end| reg.base..end)
+            } else {
+                None
+            }
+        })
+    }
 }
 
 // SAFETY: Padding is explicit and will not contain uninitialized data.
-- 
2.34.1