linux-kernel - Re: [PATCH 1/2] usb: mtu3: add a vbus debugfs interface

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Date:   Thu, 3 Aug 2017 09:00:57 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Chunfeng Yun <chunfeng.yun@...iatek.com>
Cc:     Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH 1/2] usb: mtu3: add a vbus debugfs interface

On Thu, Aug 03, 2017 at 04:37:18PM +0800, Chunfeng Yun wrote:
> +static ssize_t ssusb_vbus_write(struct file *file,
> +	const char __user *ubuf, size_t count, loff_t *ppos)
> +{
> +	struct seq_file *sf = file->private_data;
> +	struct ssusb_mtk *ssusb = sf->private;
> +	struct otg_switch_mtk *otg_sx = &ssusb->otg_switch;
> +	char buf[16];
> +
> +	if (copy_from_user(&buf, ubuf, min_t(size_t, sizeof(buf) - 1, count)))
> +		return -EFAULT;
> +
> +	if (!strncmp(buf, "on", 2)) {
> +		ssusb_set_vbus(otg_sx, 1);
> +	} else if (!strncmp(buf, "off", 3)) {
> +		ssusb_set_vbus(otg_sx, 0);

kstrtobool() is better to use here.

> +static int ssusb_debugfs_init(struct ssusb_mtk *ssusb)
>  {
>  	struct dentry *root;
>  	struct dentry *file;
>  
>  	root = debugfs_create_dir(dev_name(ssusb->dev), usb_debug_root);
>  	if (IS_ERR_OR_NULL(root)) {

That test is wrong, you should never need to care about the return value
of a debugfs call.  You can always just use it in your next call (if it
is a dentry *), or just ignore it.

> -		if (!root)
> -			dev_err(ssusb->dev, "create debugfs root failed\n");
> -		return;
> +		dev_err(ssusb->dev, "create debugfs root failed\n");
> +		goto err_dbgfs;
>  	}
>  	ssusb->dbgfs_root = root;
>  
> -	file = debugfs_create_file("mode", S_IRUGO | S_IWUSR, root,
> -			ssusb, &ssusb_mode_fops);
> -	if (!file)
> -		dev_dbg(ssusb->dev, "create debugfs mode failed\n");
> +	file = debugfs_create_file("mode", 0644, root, ssusb, &ssusb_mode_fops);
> +	if (!file) {
> +		dev_err(ssusb->dev, "create debugfs mode failed\n");

Same here, do not care, as it does not matter.  Actually, you don't even
need to keep the file pointer around, right?

> +		goto err_dbgfs;
> +	}
> +
> +	file = debugfs_create_file("vbus", 0644, root, ssusb, &ssusb_vbus_fops);
> +	if (!file) {

Same here, you don't care if debugfs fails or not, it should never
affect your code flow.

And don't you need to remove the directory when your module/hardware is
removed?  I don't see that happening here as you are not saving root off
anywhere.

thanks,

greg k-h