Re: [PATCH v12 02/22] gpu: nova-core: gsp: Extract usable FB region from GSP

["Alexandre Courbot" <acourbot@nvidia.com>]

On Sun Apr 26, 2026 at 6:14 AM JST, Joel Fernandes wrote:
> 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>
> 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 | 45 +++++++++++++++++++++++-
>  2 files changed, 52 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/nova-core/gsp/commands.rs b/drivers/gpu/nova-core/gsp/commands.rs
> index c89c7b57a751..d18abd8b5f04 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.first_usable_fb_region().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..a34d29280430 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 +126,44 @@ 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 [`Range<u64>`].
> +    /// 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).

"can use GPU memory compression for saving bandwidth" maybe?

> +    /// - 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.
> +    pub(crate) fn first_usable_fb_region(&self) -> Option<Range<u64>> {

Let's be forward-thinking, and turn this method into
`usable_fb_regions_iter`, returning an iterator. It is trivial to do
(just turn `find_map` into `filter`), we will need it later, and for now
the caller can just do `next()` to get the first region.