On Wed, 3 Feb 2016, Oliver Neukum wrote:

> Some devices I got show an inability to operate right after
> power on if they are already connected. They are beyond recovery
> if the descriptors are requested multiple times. So in case of
> a timeout we rather bail early and reset again.
> 
> This patch is a rework of a patch that fell through the cracks.
> http://www.spinics.net/lists/linux-usb/msg103263.html
> 
> Signed-off-by: Oliver Neukum <oneu...@suse.com>
> CC: sta...@vger.kernel.org
> ---
>  drivers/usb/core/hub.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index f912fe6..2124c4e 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -4496,7 +4496,12 @@ hub_port_init(struct usb_hub *hub, struct usb_device 
> *udev, int port1,
>                                               r = -EPROTO;
>                                       break;
>                               }
> -                             if (r == 0)
> +                             /*
> +                              * Some devices time out if they are powered on
> +                              * when already connected. They need a second
> +                              * reset.
> +                              */
> +                             if (r == 0  || r == -ETIMEDOUT)
>                                       break;
>                       }
>                       udev->descriptor.bMaxPacketSize0 =
> 

Hmmm.  Your device fails completely if there are multiple attempts 
without a reset in between, right?

What about devices which always time out the first control request
after a reset?  I can't be certain any such devices exist, but it
wouldn't be surprising given the range of hardware bugs in USB devices.

Would it be safer to do this instead?

                                if (r == 0 || (r == -ETIMEDOUT &&
                                                j = 0))
                                        break;

Alan Stern

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