linux-kernel - Re: Enable CONFIG_USB_SUSPEND by default or some mobile HD can't be unplugged safely

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Date:	Thu, 1 Jan 2009 12:29:51 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Yan Li <elliot.li.tech@...il.com>
cc:	gregkh@...e.de, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: Enable CONFIG_USB_SUSPEND by default or some mobile HD can't be
 unplugged safely

On Fri, 2 Jan 2009, Yan Li wrote:

> Hello List,
> 
> By default CONFIG_USB_SUSPEND is not enabled and today I got bite by
> this when I got a new WDC My Book hard drive. I have no way to unplug
> it safely, according to it's manual, with a kernel that doesn't have
> CONFIG_USB_SUSPEND=y.
> 
> On it's manual read "you should unplug and remove the device only when
> the light is off."

It's not clear whether you should believe this.  The manual may have 
overstated things.  Still, better to be safe.

>  On Linux unmounting it won't turn it's light off
> and I can feel it's motor is still running.  The only way to unplug it
> properly on a Linux system, as to my knowledge, is to echo `suspend'
> to `/sys/bus/usb/devices/$DEV/power/level'. And one has to have
> CONFIG_USB_SUSPEND=y to do this.
> 
> On Windows and Mac OS, `safely remove this device' function effectly
> turns it into `suspend' mode, and it's light off.

Yes -- but they don't suspend the device; instead they disable its 
upstream port.  As far as the device is concerned, there's no 
difference.  However the Linux API doesn't include any way to disable a 
USB port.  Maybe we should add one...

> I'm new in this field and I understood people's concern on enabling
> autosuspend.  As to my understanding, `enabling suspend' and `enabling
> autosuspend' should be controlled by two different knobs.

They are.

>  I did a
> quick search in LKML and haven't found specific oppose to enable USB
> suspend by default, and Debian has started shipping a kernel with
> it turned on since 2.6.26.
> 
> Perhaps we should consider turning it on by default?  Thanks!

That is indeed the next step to take.

Alan Stern

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