linux-kernel - Re: [PATCH] nova-core: remove an unnecessary register read: HWCFG1

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Message-ID: <a0a0c618-0b23-437b-891f-ee530c79fb6a@nvidia.com>
Date: Fri, 24 Oct 2025 18:56:44 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Alexandre Courbot <acourbot@...dia.com>,
 Joel Fernandes <joelagnelf@...dia.com>, Timur Tabi <ttabi@...dia.com>,
 Alistair Popple <apopple@...dia.com>, Edwin Peer <epeer@...dia.com>,
 Zhi Wang <zhiw@...dia.com>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Bjorn Helgaas <bhelgaas@...gle.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 <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
 nouveau@...ts.freedesktop.org, rust-for-linux@...r.kernel.org,
 LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nova-core: remove an unnecessary register read: HWCFG1

On 10/24/25 6:24 PM, John Hubbard wrote:
> This register read is not required in order to bring up any of the GPUs,
> and it is read too early on Hopper/Blackwell+ GPUs anyway. So just stop
> doing this.
> 
> Signed-off-by: John Hubbard <jhubbard@...dia.com>
> ---

I temporarily overlooked the dependency of a follow-on patch, so this
single patch here can be ignored, please. (It's also harmless to apply
it, due to git's behavior with identical patches.)

I've included this identical patch in a 2-patch series that can be used
instead:

    [PATCH 0/2] nova-core: remove HWCFG1 and need_riscv [1] 

[1] https://lore.kernel.org/20251025014050.585153-1-jhubbard@nvidia.com


thanks,
John Hubbard

> 
> This applies cleanly to today's drm-rust-next.
> 
> thanks,
> John Hubbard
> 
> 
>  drivers/gpu/nova-core/falcon.rs | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/drivers/gpu/nova-core/falcon.rs b/drivers/gpu/nova-core/falcon.rs
> index 3f505b870601..ac55cbc5ac1e 100644
> --- a/drivers/gpu/nova-core/falcon.rs
> +++ b/drivers/gpu/nova-core/falcon.rs
> @@ -371,11 +371,6 @@ pub(crate) fn new(
>          bar: &Bar0,
>          need_riscv: bool,
>      ) -> Result<Self> {
> -        let hwcfg1 = regs::NV_PFALCON_FALCON_HWCFG1::read(bar, &E::ID);
> -        // Check that the revision and security model contain valid values.
> -        let _ = hwcfg1.core_rev()?;
> -        let _ = hwcfg1.security_model()?;
> -
>          if need_riscv {
>              let hwcfg2 = regs::NV_PFALCON_FALCON_HWCFG2::read(bar, &E::ID);
>              if !hwcfg2.riscv() {
> 
> base-commit: d3917368ebc5cd89d7d08eab4673e5c4c73ff42f