linux-kernel - Re: [PATCH RFC/RFT 1/1] misc: add simple logic analyzer using polling

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Message-ID: <CAMpxmJWihGgdThmisvqjpvK6NsORg1+SOE7+wz4HZVkM5Xj77A@mail.gmail.com>
Date:   Thu, 1 Apr 2021 16:25:38 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Wolfram Sang <wsa+renesas@...g-engineering.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH RFC/RFT 1/1] misc: add simple logic analyzer using polling

On Thu, Apr 1, 2021 at 3:08 PM Linus Walleij <linus.walleij@...aro.org> wrote:
>
> On Tue, Mar 30, 2021 at 10:58 AM Wolfram Sang
> <wsa+renesas@...g-engineering.com> wrote:
>
> > This is a simple logic analyzer using GPIO polling. It comes with a
> > script to isolate a CPU for polling. While this is definately not a
> > production level analyzer, it can be a helpful first view when remote
> > debugging. Read the documentation for details.
> >
> > Signed-off-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
>
> I am a great supporter of this idea.
>
> When we created gpiod_get_array_value() and friends, the idea
> was exactly to be able to do things like this. It's a good way to
> utilize the fact that several GPIO lines can often be read from a single
> register read.
>
> > +    i2c-analyzer {
> > +            compatible = "gpio-logic-analyzer";
> > +            probe-gpios = <&gpio6 21 GPIO_OPEN_DRAIN>, <&gpio6 4 GPIO_OPEN_DRAIN>;
> > +            probe-names = "SCL", "SDA";
> > +    };
> > +
> > +The binding documentation is in the ``misc`` folder of the Kernel binding
> > +documentation.
> (...)
> > +++ b/Documentation/devicetree/bindings/misc/gpio-logic-analyzer.yaml
>
> When other debugging tools for GPIO got DT bindings it was concluded that
> it is possible to create bindings like this for debugging without even
> specifying
> any formal bindings. They are just for debugging after all.
>
> Personally I like the bindings anyway.
>
> > diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
>
> I would consider housing this tool under drivers/gpio actually.
> We have other funky things like gpio-sim and gpio-aggregator
> so why not.
>

We have actually created a sub-menu for "Virtual GPIO drivers".

> I would create a Kconfig menu with "GPIO hardware hacking tools".
>
> But Bartosz would need to agree on that idea.
>

It's perfect! If we ever get something like a generic bitbanging
driver or something, it could go in there too.

Bart

> > +config GPIO_LOGIC_ANALYZER
> > +       tristate "Simple GPIO logic analyzer"
> > +       depends on GPIOLIB || COMPILE_TEST
> > +       help
>
> depends on EXPERT
>
> I would say. Definitely not something for the average user.
>
> Yours,
> Linus Walleij