Re: [PATCH v9 04/23] gpu: nova-core: gsp: Extract usable FB region from GSP

[Joel Fernandes]

On Fri, Mar 13, 2026 at 03:58:35PM +0900, Eliot Courtney wrote:
> On Wed Mar 11, 2026 at 9:39 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 via
> > usable_fb_region() API for use by the memory subsystem.
> >
> > Cc: Nikola Djukic <ndjukic@xxxxxxxxxx>
> > Signed-off-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>
> > ---
> >  drivers/gpu/nova-core/gsp/commands.rs    | 11 ++++++--
> >  drivers/gpu/nova-core/gsp/fw/commands.rs | 32 ++++++++++++++++++++++++
> >  2 files changed, 41 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/nova-core/gsp/commands.rs b/drivers/gpu/nova-core/gsp/commands.rs
> > index 8f270eca33be..8d5780d9cace 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, //
> >  };
> >  
> > @@ -186,22 +187,28 @@ 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,
> >          _sbuffer: &mut SBufferIter<array::IntoIter<&[u8], 2>>,
> >      ) -> Result<Self, Self::InitError> {
> > +        let (base, size) = msg.first_usable_fb_region().ok_or(ENODEV)?;
> > +
> >          Ok(GetGspStaticInfoReply {
> >              gpu_name: msg.gpu_name_str(),
> > +            usable_fb_region: base..base.saturating_add(size),
> 
> We already return a Result here, so why not use checked_add?:
> `base..base.checked_add(size).ok_or(EOVERFLOW)?`

Hmm, I think I was trying to play it safe and handle any situation of a
corrupted size. But granted, it may be better to error out.

> 
> >          })
> >      }
> >  }
> > diff --git a/drivers/gpu/nova-core/gsp/fw/commands.rs b/drivers/gpu/nova-core/gsp/fw/commands.rs
> > index 67f44421fcc3..cef86cab8a12 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;
> >  
> > @@ -115,6 +116,37 @@ 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).
> 
> Are the above conditions all required (AND) or any required (OR)?
> Might be worth clarifying in the doc.

I am not sure if any clarification is needed there but I will
reword to 'Usable regions are those that satisfy all of the following:'.

> 
> > +    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.
> 
> Is it normal that it returns a bunch of broken regions?

Not really. The aim was to make the code robust at a time when I was studying
the FB regions. I will change the comment, and/or drop the check. Thanks for
pointing it out.

> > +                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));
> 
> This is identifying a range, so how about returning Option<Range<u64>>
> instead? It gets immediately converted into a range anyway.

Sure, that works.

--
Joel Fernandes