linux-kernel - Re: [PATCH v2 08/12] nova-core: sequencer: Add register opcodes

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Message-ID: <7d1f0b6b-976e-4b89-b780-1393608092d6@nvidia.com>
Date: Wed, 5 Nov 2025 15:27:04 -0800
From: John Hubbard <jhubbard@...dia.com>
To: Timur Tabi <ttabi@...dia.com>, Joel Fernandes <joelagnelf@...dia.com>
Cc: "dakr@...nel.org" <dakr@...nel.org>, "lossin@...nel.org"
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Subject: Re: [PATCH v2 08/12] nova-core: sequencer: Add register opcodes

On 11/5/25 3:19 PM, Timur Tabi wrote:
> On Wed, 2025-11-05 at 13:55 -0800, John Hubbard wrote:
>>> #define nvdev_trace(d,f,a...) nvdev_printk((d), TRACE,   info, f, ##a)
>>> #define nvdev_spam(d,f,a...)  nvdev_printk((d),  SPAM,    dbg, f, ##a)
>>
>> ...and those are unusable, unfortunately. I've tried.
> 
> This works great for me:
> 
> modprobe nouveau dyndbg="+p" modeset=1 debug="gsp=spam" config=NvGspRm=1
> 
> I get all sequencer messages when I boot with these options.

And so do I. What I meant by "unusable" is that there are so many
messages that they never really catch up (I'm throttling things
due to my use of console=ttyS0,115200: serial connection, haha).


> 
>> ftrace/bpftrace, maybe those are the real way to "trace"...or something
>> other than this.
> 
> You could say the same thing about most dev_dbg() statements.

Not for Nova, not so far. I'm trying to hold the line, so that our
dev_dbg() output is merely "almost excessive". I'm actually quite
pleased with things so far, and this last comment is merely a
tweak in order to keep things on track.

> 
> I agree that dev_dbg for sequencer commands is excessive, and that implementing new debug levels
> just to get sequencer prints is also excessive.  But Nouveau implement nvkm_trace for a reason.  And
> we all know that because of ? in Rust, NovaCore does a terrible job at telling us where an error
> actually occurred.  So there is a lot of room for improvement.

There is room to improve, but I don't think that Nouveau's logging
approach is exactly, precisely the way to go.

Let's keep thinking about it, longer term.

thanks,
-- 
John Hubbard