linux-kernel - Re: [PATCH 08/16] gpu: nova-core: wait for GFW

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Message-ID: <aAd9ZlV5_qokiFYn@cassiopeiae>
Date: Tue, 22 Apr 2025 13:28:38 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Joel Fernandes <joelagnelf@...dia.com>
Cc: 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>,
	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>,
	Jonathan Corbet <corbet@....net>,
	John Hubbard <jhubbard@...dia.com>, Ben Skeggs <bskeggs@...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 08/16] gpu: nova-core: wait for GFW_BOOT completion

On Mon, Apr 21, 2025 at 05:45:33PM -0400, Joel Fernandes wrote:
> On 4/20/2025 8:19 AM, Alexandre Courbot wrote:
> > diff --git a/drivers/gpu/nova-core/devinit.rs b/drivers/gpu/nova-core/devinit.rs
> > new file mode 100644
> > index 0000000000000000000000000000000000000000..ee5685aff845aa97d6b0fbe9528df9a7ba274b2c
> > --- /dev/null
> > +++ b/drivers/gpu/nova-core/devinit.rs
> > @@ -0,0 +1,40 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +//! Methods for device initialization.
> 
> Let us clarify what devinit means.
> 
> devinit is a sequence of register read/writes after reset that performs tasks
> such as:
> 1. Programming VRAM memory controller timings.
> 2. Power sequencing.
> 3. Clock and PLL configuration.
> 4. Thermal management.
> 5. Performs VRAM memory scrubbing (ECC initialization) - on some GPUs, it scrubs
> only part of memory and then kicks of 'async scrubbing'.
> 
> devinit itself is a 'script' which is interpreted by the PMU microcontroller of
> of the GPU by an interpreter program.
> 
> Note that devinit also needs to run during suspend/resume at runtime.

Thanks for writing this up. I fully agree that those things have to be
documented.

> 
> I talked with Alex and I could add a new patch on top of this patch to add these
> clarifying 'doc' comments as well. I will commit them to my git branch and send
> on top of this as needed, but Alex can feel free to decide to squash them as well.

Fine with both, whatever you guys prefer.

> 
> > +
> > +use kernel::bindings;
> > +use kernel::devres::Devres;
> > +use kernel::prelude::*;
> > +
> > +use crate::driver::Bar0;
> > +use crate::regs;
> > +
> > +/// Wait for devinit FW completion.
> > +///
> > +/// Upon reset, the GPU runs some firmware code to setup its core parameters. Most of the GPU is
> > +/// considered unusable until this step is completed, so it must be waited on very early during
> > +/// driver initialization.
> > +pub(crate) fn wait_gfw_boot_completion(bar: &Devres<Bar0>) -> Result<()> {
> 
> To reduce acronym soup, we can clarify gfw means 'GPU firmware', it is a broad
> term used for VBIOS ROM components several of which execute before the driver
> loads. Perhaps that part of comment can be 'the GPU firmware (gfw) code'.

Yes, we should absolutely explain acronyms as well as use consistent and defined
terminology when referring to things.

I think we should put both into Documentation/gpu/nova/ and add the
corresponding pointers in the code.

> I find this Rust convention for camel casing long constants very unreadable and
> troubling: Pgc6AonSecureScratchGroup05. I think we should relax this requirement
> for sake of readability. Could the Rust community / maintainers provide some input?
> 
> Apart from readability, it also makes searching for the same register name a
> nightmare with other code bases written in C.
> 
> Couple of ideas discussed:
> 
> 1. May be have a macro that converts
> REG(NV_PGC6_AON_SECURE_SCRATCH_GROUP_05_PRIV_LEVEL_MASK) ->
> regs::Pgc6AonSecureScratchGroup05 ?
> But not sure what it takes on the rust side to implement a macro like that.
> 
> 2. Adding doc comments both in regs.rs during defining the register, and
> possibly at the caller site. This still does address the issue fully.

If that addresses your concern, it sounds totally reasonable to me.