linux-kernel - Re: [PATCH v4 13/20] gpu: nova-core: register sysmem flush page

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Message-ID: <44f13ec88af918893e2a4b7050dce9ac184e3b75.camel@redhat.com>
Date: Fri, 30 May 2025 17:57:44 -0400
From: Lyude Paul <lyude@...hat.com>
To: Alexandre Courbot <acourbot@...dia.com>, Miguel Ojeda
 <ojeda@...nel.org>,  Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng
 <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
 Björn Roy Baron	 <bjorn3_gh@...tonmail.com>, Benno
 Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, 
 Danilo Krummrich	 <dakr@...nel.org>, David Airlie <airlied@...il.com>,
 Simona Vetter	 <simona@...ll.ch>, Maarten Lankhorst
 <maarten.lankhorst@...ux.intel.com>,  Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>
Cc: John Hubbard <jhubbard@...dia.com>, Ben Skeggs <bskeggs@...dia.com>, 
 Joel Fernandes <joelagnelf@...dia.com>, Timur Tabi <ttabi@...dia.com>,
 Alistair Popple <apopple@...dia.com>, 	linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org, 	nouveau@...ts.freedesktop.org,
 dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v4 13/20] gpu: nova-core: register sysmem flush page

On Wed, 2025-05-21 at 15:45 +0900, Alexandre Courbot wrote:
> Reserve a page of system memory so sysmembar can perform a read on it if
> a system write occurred since the last flush. Do this early as it can be
> required to e.g. reset the GPU falcons.
> 
> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
> ---
>  drivers/gpu/nova-core/gpu.rs  | 45 +++++++++++++++++++++++++++++++++++++++++--
>  drivers/gpu/nova-core/regs.rs | 10 ++++++++++
>  2 files changed, 53 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
> index 50417f608dc7b445958ae43444a13c7593204fcf..a4e2cf1b529cc25fc168f68f9eaa6f4a7a9748eb 100644
> --- a/drivers/gpu/nova-core/gpu.rs
> +++ b/drivers/gpu/nova-core/gpu.rs
> @@ -2,6 +2,7 @@
>  
>  use kernel::{device, devres::Devres, error::code::*, pci, prelude::*};
>  
> +use crate::dma::DmaObject;
>  use crate::driver::Bar0;
>  use crate::firmware::{Firmware, FIRMWARE_VERSION};
>  use crate::gfw;
> @@ -158,12 +159,32 @@ fn new(bar: &Bar0) -> Result<Spec> {
>  }
>  
>  /// Structure holding the resources required to operate the GPU.
> -#[pin_data]
> +#[pin_data(PinnedDrop)]
>  pub(crate) struct Gpu {
>      spec: Spec,
>      /// MMIO mapping of PCI BAR 0
>      bar: Devres<Bar0>,
>      fw: Firmware,
> +    /// System memory page required for flushing all pending GPU-side memory writes done through
> +    /// PCIE into system memory.
> +    sysmem_flush: DmaObject,
> +}
> +
> +#[pinned_drop]
> +impl PinnedDrop for Gpu {
> +    fn drop(self: Pin<&mut Self>) {
> +        // Unregister the sysmem flush page before we release it.
> +        let _ = self.bar.try_access_with(|b| {
> +            regs::NV_PFB_NISO_FLUSH_SYSMEM_ADDR::default()
> +                .set_adr_39_08(0)
> +                .write(b);
> +            if self.spec.chipset >= Chipset::GA102 {
> +                regs::NV_PFB_NISO_FLUSH_SYSMEM_ADDR_HI::default()
> +                    .set_adr_63_40(0)
> +                    .write(b);
> +            }
> +        });
> +    }
>  }
>  
>  impl Gpu {
> @@ -187,10 +208,30 @@ pub(crate) fn new(
>          gfw::wait_gfw_boot_completion(bar)
>              .inspect_err(|_| dev_err!(pdev.as_ref(), "GFW boot did not complete"))?;
>  
> +        // System memory page required for sysmembar to properly flush into system memory.
> +        let sysmem_flush = {
> +            let page = DmaObject::new(pdev.as_ref(), kernel::bindings::PAGE_SIZE)?;
> +
> +            // Register the sysmem flush page.
> +            let handle = page.dma_handle();
> +
> +            regs::NV_PFB_NISO_FLUSH_SYSMEM_ADDR::default()
> +                .set_adr_39_08((handle >> 8) as u32)
> +                .write(bar);
> +            if spec.chipset >= Chipset::GA102 {
> +                regs::NV_PFB_NISO_FLUSH_SYSMEM_ADDR_HI::default()
> +                    .set_adr_63_40((handle >> 40) as u32)
> +                    .write(bar);
> +            }
> +

Small nit - would it make sense for us to just add a function for initiating a
sysmem memory flush that you could pass the bar to? Seems like it might be a
bit less error prone if we end up having to do this elsewhere

> +            page
> +        };
> +
>          Ok(pin_init!(Self {
>              spec,
>              bar: devres_bar,
> -            fw
> +            fw,
> +            sysmem_flush,
>          }))
>      }
>  }
> diff --git a/drivers/gpu/nova-core/regs.rs b/drivers/gpu/nova-core/regs.rs
> index cba442da51181971f209b338249307c11ac481e3..b599e7ddad57ed8defe0324056571ba46b926cf6 100644
> --- a/drivers/gpu/nova-core/regs.rs
> +++ b/drivers/gpu/nova-core/regs.rs
> @@ -38,6 +38,16 @@ pub(crate) fn chipset(self) -> Result<Chipset> {
>      }
>  }
>  
> +/* PFB */
> +
> +register!(NV_PFB_NISO_FLUSH_SYSMEM_ADDR @ 0x00100c10 {
> +    31:0    adr_39_08 as u32;
> +});
> +
> +register!(NV_PFB_NISO_FLUSH_SYSMEM_ADDR_HI @ 0x00100c40 {
> +    23:0    adr_63_40 as u32;
> +});
> +
>  /* PGC6 */
>  
>  register!(NV_PGC6_AON_SECURE_SCRATCH_GROUP_05_PRIV_LEVEL_MASK @ 0x00118128 {
> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat

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