linux-kernel - Re: [PATCH v8 4/8] i2c: Introduce OF component probe function

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Message-ID: <CAD=FV=WRSjk3U9Kau0wqkgv3KB=9jM6wCM9Gs-WxWai35sfxTg@mail.gmail.com>
Date: Tue, 15 Oct 2024 10:58:31 -0700
From: Doug Anderson <dianders@...omium.org>
To: Chen-Yu Tsai <wenst@...omium.org>
Cc: Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...gle.com>, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Wolfram Sang <wsa@...nel.org>, 
	Benson Leung <bleung@...omium.org>, Tzung-Bi Shih <tzungbi@...nel.org>, 
	chrome-platform@...ts.linux.dev, devicetree@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, Johan Hovold <johan@...nel.org>, 
	Jiri Kosina <jikos@...nel.org>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
	linux-i2c@...r.kernel.org
Subject: Re: [PATCH v8 4/8] i2c: Introduce OF component probe function

Hi,

On Tue, Oct 8, 2024 at 12:35 AM Chen-Yu Tsai <wenst@...omium.org> wrote:
>
> +int i2c_of_probe_component(struct device *dev, const struct i2c_of_probe_cfg *cfg, void *ctx)
> +{
> +       const struct i2c_of_probe_ops *ops;
> +       const char *type;
> +       struct i2c_adapter *i2c;
> +       int ret;
> +
> +       ops = cfg->ops ?: &i2c_of_probe_dummy_ops;
> +       type = cfg->type;
> +
> +       struct device_node *i2c_node __free(device_node) = i2c_of_probe_get_i2c_node(dev, type);
> +       if (IS_ERR(i2c_node))
> +               return PTR_ERR(i2c_node);

I'm still getting comfortable with the __free() syntax so sorry if I'm
wrong, but I _think_ the above is buggy. I believe that the definition
of the free function for "device_node" is from:

DEFINE_FREE(device_node, struct device_node *, if (_T) of_node_put(_T))

...which means it'll call of_node_put() to free "i2c_node" when it
goes out of scope. of_node_put() handles NULL pointers but _not_ ERR
pointers. So I think that if you get an error back and then return via
the PTR_ERR(i2c_node) then it'll crash because it will try to free an
ERR pointer. Did I get that right? Presumably you need to instead do:

  return PTR_ERR(no_free_ptr(i2c_node));

...or change of_node_put() to be a noop for error pointers?


> +struct i2c_of_probe_ops {
> +       /**
> +        * @enable: Retrieve and enable resources so that the components respond to probes.
> +        *
> +        * Resources should be reverted to their initial state before returning if this fails.

nit: might be worth explicitly noting that returning -EPROBE_DEFER is
OK here because this both retrieves resources and enables.


> +        */
> +       int (*enable)(struct device *dev, struct device_node *bus_node, void *data);
> +
> +       /**
> +        * @cleanup_early: Release exclusive resources prior to enabling component.

nit: change the word "enabling" to "calling probe() on a detected"
since otherwise it could be confused with the "enable" function above.


-Doug