Re: xHCI problem? [was Re: Erratic USB device behavior and device loss]

Alan Stern
2016-09-15T14:16:49Z

On Thu, 15 Sep 2016, Ulf Hansson wrote:

> > The situation isn't any better. At the start of the trace,
> > the device is in runtime suspend but there are many attempts to
> > communicate with it, all of which fail.
>
> It's really weird. Have this driver ever worked!? :-)

Probably not. Or at least, not with runtime PM.

> > Then a little less than an hour after the trace started, the device was
> > resumed. At that point it started working okay. Until there was a
> > spontaneous disconnect.
> >
> > The device reconnected, but after 3 seconds it was runtime suspended
> > again -- and the I/O attempts continued. Some time later there was
> > another runtime resume, and the device began working again. Until
> > another spontaneous disconnect occurred. And so on...
> >
> > Ulf, we really need to figure out why the autosuspends are occurring
> > and why the I/O doesn't stop while the device is suspended.
>
> Okay, let's see.
>
> I had another look in the rtsx_usb_sdmmc driver. Apparently it
> registers a led classdev. Updating the led is done from a work, by
> calling rtsx_usb_turn_on|off_led(), which do access the usb device.
> These calls are not properly managed by runtime PM, so I have fixed
> those according to below change:
>
> ---
> drivers/mmc/host/rtsx_usb_sdmmc.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/mmc/host/rtsx_usb_sdmmc.c
> b/drivers/mmc/host/rtsx_usb_sdmmc.c
> index 6c71fc9..a59c7fa 100644
> --- a/drivers/mmc/host/rtsx_usb_sdmmc.c
> +++ b/drivers/mmc/host/rtsx_usb_sdmmc.c
> @@ -1314,6 +1314,7 @@ static void rtsx_usb_update_led(struct work_struct *work)
> container_of(work, struct rtsx_usb_sdmmc, led_work);
> struct rtsx_ucr *ucr = host->ucr;
>
> + pm_runtime_get_sync(sdmmc_dev(host));
> mutex_lock(&ucr->dev_mutex);
>
> if (host->led.brightness == LED_OFF)
> @@ -1322,6 +1323,7 @@ static void rtsx_usb_update_led(struct work_struct *work)
> rtsx_usb_turn_on_led(ucr);
>
> mutex_unlock(&ucr->dev_mutex);
> + pm_runtime_put(sdmmc_dev(host));
> }
> #endif
>
> --
>
> Although, I doubt the above is the main reason to the issues we see.

I don't know -- it could well be the reason. The symptoms are
definitely what you would expect to see if some thread was doing I/O
without calling the pm_runtime_* routines.

> Instead I think somehow the parent device (usb device) isn't being
> properly managed through runtime PM, but not due to wrong deployment
> in the mmc core nor in the rtsx_usb_driver, but at some place else.
> :-)
>
> I started looking for calls to pm_suspend_ignore_children(dev, true),
> which would decouple the usb device from the mmc platform device from
> a runtime PM point of view. I found one suspicious case!
>
> drivers/usb/storage/realtek_cr.c:
> pm_suspend_ignore_children(&us->pusb_intf->dev, true);
>
> As I am not so familiar with USB, I can't really tell why the above
> exists, although perhaps just removing that line would be worth a
> try!?

No, the realtek_cr driver has no connection with this. It's a
sub-module of the usb_storage driver; it uses the SCSI interface,
not the MMC interface.

> If neither of the above works, the next step could be to start
> checking error codes in the mmc core and in the rtsx_usb_sdmmc driver,
> from the calls to pm_runtime_get|put() and pm_runtime_enable().

Let's see what this patch does.

Alan Stern