Disapearing pl2303 usb serial adapter on rpi2

[bob prohaska]

On Wed, Dec 20, 2017 at 09:13:12PM +0200, Jukka A. Ukkonen wrote:
> On 12/20/17 19:02, bob prohaska wrote:
> > On an RPI2 at r326951 a pl2303 usb-serial adapter seems to be locking up
> > after a few hours. In the past this could be rectified by using usbconfig
> > to power cycle it, but now even that doesn't work. Apart from the serial
> > device file vanishing from /dev there seems to be no other ill effect.
> > Rebooting fixes the problem for minutes to hours.
> > 
> > There is no explict error report in dmesg, but when usbconfig tries to power
> > cycle the adapter the console reports:
> > 
> > uhub_explore_handle_re_enumerate: Could not unconfigure device (ignored)
> > usbd_req_re_enumerate: addr=9, set address failed! (USB_ERR_IOERROR, ignored)
> > usbd_setup_device_desc: getting device descriptor at addr 9 failed, USB_ERR_IOERROR
> > usbd_req_re_enumerate: addr=9, set address failed! (USB_ERR_STALLED, ignored)
> > usbd_setup_device_desc: getting device descriptor at addr 9 failed, USB_ERR_STALLED
> > 
> > 
> > A second RPI2 running r326747 is subject to the same lockup, but the adapter
> > can be unstuck using usbconfig to power cycle it.
> > 
> > 
> > Are there any diagnostics which could shed more light on the problem?
> > 
> > Thanks for reading,
> > 
> > bob prohaska
> > 
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> 
> 
> 
> 
> So, my guess is that the poor RPI is unable to drive enough power
> to your pl2303. Esp. when there are multiple USB devices draining
> power you will eventually exceed the RPI's power output capacity.
> As a result you will see a magically vanishing and reappearing USB
> device.

The Pi is on a 2.5 amp power supply, the other usb loads are a keyboard,
mouse and USB flash drive, so it's unlikely to be a power issue. The problem
seems to have gotten worse with the latest -current, which is what motivated
my post. It's been suggested to simply give up on pl2303 devices and use 
ftdi but I've resisted the urge because the pl2303 adapters work fine on
Mac OS and Raspbian. 

The adapters work correctly with Prolific's drivers and are not identified
as impostors. Testing disclosed that unpowering the USB end of the adapter
does not suffice to unstick it, but unpowering both ends does allow it to 
reset. Hopefully it's an initialization issue. 

Thanks for reading!

bob prohaska