linux-kernel - Re: [PATCH v8 1/1] gpio: add sloppy logic analyzer using polling

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Date:   Fri, 2 Jun 2023 00:39:25 +0300
From:   andy.shevchenko@...il.com
To:     Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v8 1/1] gpio: add sloppy logic analyzer using polling

Tue, Mar 29, 2022 at 11:11:26AM +0200, Wolfram Sang kirjoitti:
> This is a sloppy logic analyzer using GPIOs. It comes with a script to
> isolate a CPU for polling. While this is definitely not a production
> level analyzer, it can be a helpful first view when remote debugging.
> Read the documentation for details.

One note since I have done recent review and realize one issue with debugfs.

...

> +	priv->debug_dir = debugfs_create_dir(devname, gpio_la_poll_debug_dir);

If this fails with NULL...

> +	debugfs_create_blob("meta_data", 0400, priv->debug_dir, &priv->meta);
> +	debugfs_create_ulong("delay_ns", 0600, priv->debug_dir, &priv->delay_ns);
> +	debugfs_create_ulong("delay_ns_acquisition", 0400, priv->debug_dir, &priv->acq_delay);
> +	debugfs_create_file_unsafe("buf_size", 0600, priv->debug_dir, priv, &fops_buf_size);
> +	debugfs_create_file_unsafe("capture", 0200, priv->debug_dir, priv, &fops_capture);
> +	debugfs_create_file_unsafe("trigger", 0200, priv->debug_dir, priv, &fops_trigger);

...and any of these is not, we will end up with the file in a root folder of debugfs...

> +	dev_info(dev, "initialized");

...

> +static int gpio_la_poll_remove(struct platform_device *pdev)
> +{
> +	struct gpio_la_poll_priv *priv = platform_get_drvdata(pdev);
> +
> +	mutex_lock(&priv->lock);
> +	debugfs_remove_recursive(priv->debug_dir);

...and this one won't remove it.

> +	mutex_unlock(&priv->lock);
> +	mutex_destroy(&priv->lock);
> +
> +	return 0;
> +}

...

However, I haven't checked if it's pure theoretical issue with the current code
base of debugfs or a potential problem. Easy fix is to check an error code and
skip the files creation. Not sure if driver will be useful in that case.

-- 
With Best Regards,
Andy Shevchenko