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

[Joel Fernandes <joelagnelf@nvidia.com>]

On 5/2/2026 11:41 AM, Alexandre Courbot wrote:
> 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?

Done.

> 
>> +    /// - 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.

Done. Indeed, it does not add more LOC while supporting multiple regions.

thanks,
-- 
Joel Fernandes