Re: [PATCH 2/2] [RFC] pl2303 autosuspend

Am Dienstag 13 November 2007 schrieb Sarah Sharp:

> A hibernate (or a suspend that causes the USB subsystem to lose power)
> has issues.  If you have the tty open when you hibernate, a new tty will
> be created when the device re-enumerates during resume.  Closing the old

Yes, this is the desired default. Any loss of power is treated as disconnect.

> tty will cause the serial driver's shutdown function to be called on a
> device that doesn't exist anymore.  Fortunately, that doesn't seem to
> have any adverse effects on the functionality of the new tty.

This is what would happen at a hot unplug, too. Do you see any problems
therewith?
 
> I've tried adding a tty hangup to the suspend function, but that doesn't
> seem to have any effect on minicom.  I'm not sure whether minicom
> ignores hangups, or if it never gets the hangup.  The tty layer
> schedules the hangup; it isn't synchronous.

As disconnect() is called, the generic USB serial layer will call hangup
anyway from usb_serial_disconnect().

> This seems to be the only issue with adding autosuspend code to the
> pl2303.  A hibernate with the tty open didn't work before, so I'm
> inclined to send an updated patch later today.
> 
> Also, I found out the hard way that some types of pl2303 chips don't

I feel your pain.

> handle suspend correctly.  The HX chip can handle suspend gracefully,
> but the type_1 can't.  When it resumes, the host controller detects it
> as a low speed device; since it's actually a high speed device, this
> fails.  The initialization for the two chips are different (see the
> FISH/SOUP mess in pl2303.c), but I haven't experimented to see if
> different initialization would help.

By then it would be too late. IMHO the failing devices need reset_resume()
and a quirk entry.

> Is there somewhere to record devices that handle autosuspend correctly?
> I saw some mention that the HAL people will take care of it, but I
> haven't heard anything specific.

IIRC Kay Sievers is working on that.

	Regards
		Oliver

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