Subject: Re: [PATCH v4] usb: create usb_debug_root for gadget only

From: Greg Kroah-Hartman <[email-masked]>
Date: Tue, 4 Jun 2019 09:37:06 +0200

On Tue, Jun 04, 2019 at 03:34:07PM +0800, Chunfeng Yun wrote:
> When CONFIG_USB is not set, and CONFIG_USB_GADGET is set,
> there is an issue, e.g.:
> 
> drivers/usb/mtu3/mtu3_debugfs.o: in function 'ssusb_debugfs_create_root':
> mtu3_debugfs.c:(.text+0xba3): undefined reference to 'usb_debug_root'
> 
> usb_debug_root is currently only built when host is supported
> (CONFIG_USB is set), for convenience, we also want it created when
> gadget only is enabled, this patch try to support it.
> 
> Reported-by: Randy Dunlap <[email-masked]>
> Signed-off-by: Chunfeng Yun <[email-masked]>
> ---
> v4:
>   move common API into common.c suggested by Felipe
> 
> v3:
>   1. still create usb_debug_root for gadget only
>   2. abandon mtu3's change
>   3. drop acked-by Randy
> 
> v2(resend): add acked-by Randy
> 
> v1: fix mtu3's build error, replace usb_debug_root by NULL;
> ---
>  drivers/usb/common/common.c   | 26 ++++++++++++++++++++++++++
>  drivers/usb/core/usb.c        | 16 ++++------------
>  drivers/usb/gadget/udc/core.c |  3 +++
>  include/linux/usb.h           |  2 ++
>  4 files changed, 35 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/usb/common/common.c b/drivers/usb/common/common.c
> index 18f5dcf58b0d..c52e9c9f58ec 100644
> --- a/drivers/usb/common/common.c
> +++ b/drivers/usb/common/common.c
> @@ -15,6 +15,7 @@
>  #include <linux/usb/of.h>
>  #include <linux/usb/otg.h>
>  #include <linux/of_platform.h>
> +#include <linux/debugfs.h>
>  
>  static const char *const ep_type_names[] = {
>  	[USB_ENDPOINT_XFER_CONTROL] = "ctrl",
> @@ -139,6 +140,31 @@ enum usb_dr_mode usb_get_dr_mode(struct device *dev)
>  }
>  EXPORT_SYMBOL_GPL(usb_get_dr_mode);
>  
> +struct dentry *usb_debug_root;
> +EXPORT_SYMBOL_GPL(usb_debug_root);
> +
> +static atomic_t usb_debug_root_refcnt = ATOMIC_INIT(0);

Ick, no.

> +
> +struct dentry *usb_debugfs_init(void)
> +{
> +	if (!usb_debug_root)
> +		usb_debug_root = debugfs_create_dir("usb", NULL);
> +
> +	atomic_inc(&usb_debug_root_refcnt);
> +
> +	return usb_debug_root;
> +}
> +EXPORT_SYMBOL_GPL(usb_debugfs_init);
> +
> +void usb_debugfs_cleanup(void)
> +{
> +	if (atomic_dec_and_test(&usb_debug_root_refcnt)) {
> +		debugfs_remove_recursive(usb_debug_root);
> +		usb_debug_root = NULL;
> +	}
> +}
> +EXPORT_SYMBOL_GPL(usb_debugfs_cleanup);

Only remove the debugfs subdir if the usbcore module is removed.  Create
the debugfs subdir when the usbcore module is loaded.  No need for any
reference counting of any sort at all.  No need to overthink this :)

thanks,

greg k-h

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