linux-kernel - Re: [PATCHv3 1/4] usb: Provide usb_device_speed

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Date:	Sat, 20 Aug 2011 02:15:00 +0300
From:	Felipe Balbi <balbi@...com>
To:	Michal Nazarewicz <mnazarewicz@...gle.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Yang Rui Rui <ruirui.r.yang@...to.com>,
	Dave Young <hidave.darkstar@...il.com>,
	Felipe Balbi <balbi@...com>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 1/4] usb: Provide usb_device_speed_name() function

Hi,

On Sat, Aug 20, 2011 at 12:32:59AM +0200, Michal Nazarewicz wrote:
> From: Michal Nazarewicz <mina86@...a86.com>
> 
> In a few places kernel wants to print a human-readable USB
> device speed name (eg. "high") instead of a raw number
> (eg. 3).  Usually a switch is introduced in those places
> leading to code repetition.  To mitigate this issue, this
> commit introduces usb_device_speed_name() function, which
> returns a human-readable name of provided speed.
> 
> Signed-off-by: Michal Nazarewicz <mina86@...a86.com>
> ---
>  drivers/usb/Makefile          |    3 +++
>  drivers/usb/common.c          |   24 ++++++++++++++++++++++++
>  drivers/usb/gadget/udc-core.c |   19 ++-----------------
>  include/linux/usb/ch9.h       |    8 ++++++++
>  4 files changed, 37 insertions(+), 17 deletions(-)
>  create mode 100644 drivers/usb/common.c
> 
> diff --git a/drivers/usb/Makefile b/drivers/usb/Makefile
> index 30ddf8d..a3167cc 100644
> --- a/drivers/usb/Makefile
> +++ b/drivers/usb/Makefile
> @@ -51,3 +51,6 @@ obj-$(CONFIG_USB_MUSB_HDRC)	+= musb/
>  obj-$(CONFIG_USB_RENESAS_USBHS)	+= renesas_usbhs/
>  obj-$(CONFIG_USB_OTG_UTILS)	+= otg/
>  obj-$(CONFIG_USB_GADGET)	+= gadget/
> +
> +obj-$(CONFIG_USB)		+= common.o
> +obj-$(CONFIG_USB_GADGET)	+= common.o
> diff --git a/drivers/usb/common.c b/drivers/usb/common.c
> new file mode 100644
> index 0000000..e9d7141
> --- /dev/null
> +++ b/drivers/usb/common.c
> @@ -0,0 +1,24 @@
> +/*
> + * Provides code common for host and device side USB.
> + */
> +
> +#include <linux/kernel.h>  /* for ARRAY_SIZE() */
> +#include <linux/module.h>  /* for EXPORT_SYMBOL_GPL() */
> +#include <linux/usb/ch9.h>
> +
> +const char *usb_device_speed_name(enum usb_device_speed speed)

somehow usb_speed_string() sounds better to me.

> +{
> +	static const char *const names[] = {
> +		"UNKNOWN",
> +		"low-speed",
> +		"full-speed",
> +		"high-speed",
> +		"wireless",
> +		"super-speed",
> +	};
> +
> +	if (speed < 0 || speed >= ARRAY_SIZE(names))
> +		speed = USB_SPEED_UNKNOWN;

I generally dislike depending on a particular ordering of enumerations.
While's it's highly unlikely that anyone will change that, if someone
does change, then it'll take a long time to actually find the bug on the
print here :-)

I woud rather use a switch in this case.

> diff --git a/drivers/usb/gadget/udc-core.c b/drivers/usb/gadget/udc-core.c
> index 05ba472..e1ecdbc 100644
> --- a/drivers/usb/gadget/udc-core.c
> +++ b/drivers/usb/gadget/udc-core.c
> @@ -375,23 +375,8 @@ static ssize_t usb_udc_speed_show(struct device *dev,
>  		struct device_attribute *attr, char *buf)
>  {
>  	struct usb_udc		*udc = container_of(dev, struct usb_udc, dev);
> -	struct usb_gadget	*gadget = udc->gadget;
> -
> -	switch (gadget->speed) {
> -	case USB_SPEED_LOW:
> -		return snprintf(buf, PAGE_SIZE, "low-speed\n");
> -	case USB_SPEED_FULL:
> -		return snprintf(buf, PAGE_SIZE, "full-speed\n");
> -	case USB_SPEED_HIGH:
> -		return snprintf(buf, PAGE_SIZE, "high-speed\n");
> -	case USB_SPEED_WIRELESS:
> -		return snprintf(buf, PAGE_SIZE, "wireless\n");
> -	case USB_SPEED_SUPER:
> -		return snprintf(buf, PAGE_SIZE, "super-speed\n");
> -	case USB_SPEED_UNKNOWN:	/* FALLTHROUGH */
> -	default:
> -		return snprintf(buf, PAGE_SIZE, "UNKNOWN\n");
> -	}
> +	return snprintf(buf, PAGE_SIZE, "%s\n",
> +			usb_device_speed_name(udc->gadget->speed));
>  }
>  static DEVICE_ATTR(speed, S_IRUSR, usb_udc_speed_show, NULL);

you said 'several locations', but there's only one ? No other driver is
using something similar ?

-- 
balbi

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