Re: [PATCH 09/16] gpu: nova-core: register sysmem flush page

Joel Fernandes
2025-04-22T18:50:31Z

On 4/20/2025 8:19 AM, Alexandre Courbot wrote:
> A page of system memory is reserved 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@nvidia.com>
> ---
> drivers/gpu/nova-core/dma.rs | 54 ++++++++++++++++++++++++++++++++++++++
> drivers/gpu/nova-core/gpu.rs | 53 +++++++++++++++++++++++++++++++++++--
> drivers/gpu/nova-core/nova_core.rs | 1 +
> drivers/gpu/nova-core/regs.rs | 10 +++++++
> 4 files changed, 116 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/nova-core/dma.rs b/drivers/gpu/nova-core/dma.rs
> new file mode 100644
> index 0000000000000000000000000000000000000000..a4162bff597132a04e002b2b910a4537bbabc287
> --- /dev/null
> +++ b/drivers/gpu/nova-core/dma.rs
> @@ -0,0 +1,54 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Simple DMA object wrapper.
> +
> +// To be removed when all code is used.
> +#![allow(dead_code)]
> +
> +use kernel::device;
> +use kernel::dma::CoherentAllocation;
> +use kernel::page::PAGE_SIZE;
> +use kernel::prelude::*;
> +
> +pub(crate) struct DmaObject {
> + pub dma: CoherentAllocation<u8>,
> + pub len: usize,
> + #[allow(dead_code)]
> + pub name: &'static str,
> +}
> +
> +impl DmaObject {
> + pub(crate) fn new(
> + dev: &device::Device<device::Bound>,
> + len: usize,
> + name: &'static str,
> + ) -> Result<Self> {
> + let len = core::alloc::Layout::from_size_align(len, PAGE_SIZE)
> + .map_err(|_| EINVAL)?
> + .pad_to_align()
> + .size();
> + let dma = CoherentAllocation::alloc_coherent(dev, len, GFP_KERNEL | __GFP_ZERO)?;
> +
> + Ok(Self { dma, len, name })
> + }
> +
> + pub(crate) fn from_data(
> + dev: &device::Device<device::Bound>,
> + data: &[u8],
> + name: &'static str,
> + ) -> Result<Self> {
> + Self::new(dev, data.len(), name).and_then(|mut dma_obj| {
> + // SAFETY:
> + // - The copied data fits within the size of the allocated object.
> + // - We have just created this object and there is no other user at this stage.
> + unsafe {
> + core::ptr::copy_nonoverlapping(
> + data.as_ptr(),
> + dma_obj.dma.start_ptr_mut(),
> + data.len(),
> + );
> + }
> + Ok(dma_obj)
> + })
> + }
> +}
> diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
> index 1f7799692a0ab042f2540e01414f5ca347ae9ecc..d43e710cc983d51f053dacbd77cbbfb79fa882c3 100644
> --- a/drivers/gpu/nova-core/gpu.rs
> +++ b/drivers/gpu/nova-core/gpu.rs
> @@ -3,6 +3,7 @@
> use kernel::{device, devres::Devres, error::code::*, pci, prelude::*};
>
> use crate::devinit;
> +use crate::dma::DmaObject;
> use crate::driver::Bar0;
> use crate::firmware::Firmware;
> use crate::regs;
> @@ -145,12 +146,30 @@ fn new(bar: &Devres<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,

Can add here:
// System memory page required for sysmembar which is a GPU-initiated hardware
// memory-barrier operation that flushes all pending GPU-side memory writes
// that were done through PCIE, to system memory.

Will add to my git tree as well (but feel free to squash as needed).

> + 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 _ = with_bar!(&self.bar, |b| {
> + regs::PfbNisoFlushSysmemAddr::default()
> + .set_adr_39_08(0)
> + .write(b);
> + if self.spec.chipset >= Chipset::GA102 {
> + regs::PfbNisoFlushSysmemAddrHi::default()
> + .set_adr_63_40(0)
> + .write(b);
> + }
> + });
> + }
> }
>
> impl Gpu {
> @@ -173,6 +192,36 @@ pub(crate) fn new(
> devinit::wait_gfw_boot_completion(&bar)
> .inspect_err(|_| pr_err!("GFW boot did not complete"))?;
>
> - Ok(pin_init!(Self { spec, bar, fw }))
> + // System memory page required for sysmembar to properly flush into system memory.

Can elaborate more here:

// System memory page required for sysmembar which is a GPU-initiated hardware
// memory-barrier operation that flushes all GPU-side memory writes that were
// done through PCIE, to system memory. It is required for Falcon to be reset
// as the reset operation involves a reset handshake. When the falcon acks the
// reset, it writes its acknowledgement into system memory, but for this write
// to be visible to the host, it needs to do sysmembar to flush the write and
// prevent the driver from timing out.

> + let sysmem_flush = {
> + let page = DmaObject::new(
> + pdev.as_ref(),
> + kernel::bindings::PAGE_SIZE,
> + "sysmem flush page",
> + )?;
> +
> + // Register the sysmem flush page.
> + with_bar!(bar, |b| {
> + let handle = page.dma.dma_handle();
> +
> + regs::PfbNisoFlushSysmemAddr::default()
> + .set_adr_39_08((handle >> 8) as u32)
> + .write(b);
> + if spec.chipset >= Chipset::GA102 {
> + regs::PfbNisoFlushSysmemAddrHi::default()
> + .set_adr_63_40((handle >> 40) as u32)
> + .write(b);
> + }
> + })?;
> +
> + page
> + };
> +
> + Ok(pin_init!(Self {
> + spec,
> + bar,
> + fw,
> + sysmem_flush,
> + }))
> }
> }
> diff --git a/drivers/gpu/nova-core/nova_core.rs b/drivers/gpu/nova-core/nova_core.rs
> index 878161e060f54da7738c656f6098936a62dcaa93..37c7eb0ea7a926bee4e3c661028847291bf07fa2 100644
> --- a/drivers/gpu/nova-core/nova_core.rs
> +++ b/drivers/gpu/nova-core/nova_core.rs
> @@ -21,6 +21,7 @@ macro_rules! with_bar {
> }
>
> mod devinit;
> +mod dma;
> mod driver;
> mod firmware;
> mod gpu;
> diff --git a/drivers/gpu/nova-core/regs.rs b/drivers/gpu/nova-core/regs.rs
> index fd7096f0ddd4af90114dd1119d9715d2cd3aa2ac..1e24787c4b5f432ac25fe399c8cb38b7350e44ae 100644
> --- a/drivers/gpu/nova-core/regs.rs
> +++ b/drivers/gpu/nova-core/regs.rs
> @@ -14,6 +14,16 @@
> 28:20 chipset => try_into Chipset, "chipset model"
> );
>
> +/* PFB */

Also can add:

/// These two registers together hold the physical system memory address
/// that is used by the GPU for perform sysmembar operation (see gpu.rs).

> +
> +register!(PfbNisoFlushSysmemAddr@0x00100c10;
> + 31:0 adr_39_08 => as u32
> +);
> +
> +register!(PfbNisoFlushSysmemAddrHi@0x00100c40;
> + 23:0 adr_63_40 => as u32
> +);
> +

Thanks.