linux-kernel - Re: [PATCH v9 1/1] gpio: add sloppy logic analyzer using polling

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Date: Thu, 13 Jun 2024 10:17:27 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Wolfram Sang <wsa+renesas@...g-engineering.com>, Bartosz Golaszewski <brgl@...ev.pl>, 
	linux-renesas-soc@...r.kernel.org, Jonathan Corbet <corbet@....net>, 
	Linus Walleij <linus.walleij@...aro.org>, Kent Gibson <warthog618@...il.com>, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-gpio@...r.kernel.org
Subject: Re: [PATCH v9 1/1] gpio: add sloppy logic analyzer using polling

On Wed, Jun 12, 2024 at 6:03 PM Wolfram Sang
<wsa+renesas@...g-engineering.com> wrote:
>
> Hi Bart,
>
> > I really dislike drivers being called in an ambiguous way like
> > "simple" or - in this case "sloppy". I understand why it is - in fact
> > - sloppy but can we call it anything else? Like
> > "gpio-logic-analyzer.c"?
>
> Sure, we can if you prefer. I named it like this to make the limitations
> super-clear. And even with that in place, I still got a private email
> where someone wanted to build a 400MHz-RPi-based logic analyzer device
> with it. Which would not only have the latency problems, but also
> likely have a max sampling speed of whopping 400kHz.
>
> > > +Note that you must provide a name for every GPIO specified. Currently a
> > > +maximum of 8 probes are supported. 32 are likely possible but are not
> > > +implemented yet.
> > > +
> >
> > What happens on non-DT systems? Can you still create an analyzer in a
> > different way? Can I maybe interest you in configfs for the purpose of
> > device configuration like what gpio-sim and the upcoming gpio-virtuser
> > does?
>
> Frankly, I'd like to leave this to the person needing it. I've been
> working on this for way too long already and am not up to major changes
> anymore. Minor stuff, okay, I'll go one or two more rounds.
>
> The GPIO analyzer is a debug tool aimed for development boards in remote
> labs, and all boards I have access to use DT. Furthermore, debugfs is nice
> because it is clear there is no stable ABI. It has been useful as-is in
> the past. That's what I am offering. If that's not enough, no hard
> feelings, but someone else needs to continue then.
>
> All the best,

I see. I don't want to stop it from going upstream. On second thought
though: are you sure drivers/gpio/ is the right place for it? This
directory is for GPIO *providers* - mostly drivers for real HW and
some "virtual" GPIO providers (gpio-aggregator, gpio-sim, gpio-latch).
In general: modules that export their own gpio_chip. This module is a
consumer of GPIOs exclusively. May I suggest moving it over to
drivers/misc/? I think it's a better place for it and I wouldn't mind
keeping the "sloppy" in the name then.

Bart