linux-kernel - Re: [PATCH v4 08/20] gpu: nova-core: allow register aliases

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Message-Id: <DA2FLXFS10I4.1VIQE3JHJMBLJ@nvidia.com>
Date: Thu, 22 May 2025 14:14:49 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Danilo Krummrich" <dakr@...nel.org>
Cc: "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>, "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>,
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Subject: Re: [PATCH v4 08/20] gpu: nova-core: allow register aliases

On Wed May 21, 2025 at 5:37 PM JST, Danilo Krummrich wrote:
> On Wed, May 21, 2025 at 03:45:03PM +0900, Alexandre Courbot wrote:
>> Some registers (notably scratch registers) don't have a definitive
>> purpose, but need to be interpreted differently depending on context.
>> 
>> Expand the register!() macro to support a syntax indicating that a
>> register type should be at the same offset as another one, but under a
>> different name, and with different fields and documentation.
>> 
>> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
>> ---
>>  drivers/gpu/nova-core/regs/macros.rs | 40 ++++++++++++++++++++++++++++++++++--
>>  1 file changed, 38 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/gpu/nova-core/regs/macros.rs b/drivers/gpu/nova-core/regs/macros.rs
>> index 7cd013f3c90bbd8ca437d4072cae8f11d7946fcd..64dda1d4d93d3c7022ef02b6f6fb81b58e90dd44 100644
>> --- a/drivers/gpu/nova-core/regs/macros.rs
>> +++ b/drivers/gpu/nova-core/regs/macros.rs
>> @@ -71,6 +71,20 @@
>>  /// pr_info!("CPU CTL: {:#x}", cpuctl);
>>  /// cpuctl.set_start(true).write(&bar, CPU_BASE);
>>  /// ```
>> +///
>> +/// It is also possible to create a alias register by using the `=> PARENT` syntax. This is useful
>> +/// for cases where a register's interpretation depends on the context:
>> +///
>> +/// ```no_run
>> +/// register!(SCRATCH_0 @ 0x0000100, "Scratch register 0" {
>> +///    31:0     value as u32, "Raw value";
>> +///
>> +/// register!(SCRATCH_0_BOOT_STATUS => SCRATCH_0, "Boot status of the firmware" {
>
> NIT: I'd put the arrow the other way around, i.e. SCRATCH_0_BOOT_STATUS is
> derived from SCRATCH_0, not the other way around.

That's doable, but I read the current expression as
"SCRATCH_0_BOOT_STATUS points to SCRATCH_0". Also `<=` will be rendered
into an actual "inferior or equal" sign if ligature substitution is
used in your text editor.