Hi Alan, Thank you for your responses here and in another email thread. On Sun, Jul 31, 2022 at 3:17 PM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Sun, Jul 31, 2022 at 01:20:55AM -0700, Guenter Roeck wrote: > > On Sun, Jul 31, 2022 at 03:34:16AM +0100, Alexey Klimov wrote: > > > On Tue, Jul 26, 2022 at 8:48 AM Oliver Neukum <oneukum@xxxxxxxx> wrote: > > > > > > > > On 26.07.22 02:21, Alexey Klimov wrote: > > > > > On Mon, Jul 25, 2022 at 9:51 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > >> > > > > >> On Mon, Jul 25, 2022 at 04:06:05AM +0100, Alexey Klimov wrote: > > > > > > > > > > [..] > > > > > > > > > >> Anyway, driver looks good to me, nice work! > > > > >> > > > > >> Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > > > > > > > > > Thanks, Greg. If you don't mind I'll use your tag in next version > > > > > after making changes suggested by Guenter since there will be no > > > > > significant functional changes. If code will change a lot, then the > > > > > process (Documentation/process/submitting-patches.rst) will require me > > > > > to drop the tag. > > > > > > > > Hi, > > > > > > > > while thinking about this a question arose. How does this > > > > device react to a USB reset? A watchdog that can be disabled > > > > by a simple reset does not like very reliable to me. > > > > Do you need to implement pre/post_reset() ? > > > > > > You're right. Upon reset the watchdog is disabled even if it was active before. > > > Adding empty ->pre_reset() and ->post_reset() helps to avoid that, but > > > looking at Documentation and other drivers it seems that I need to do: > > > in pre_reset(): > > > mutex_lock() to block any other I/O to the usb device; > > > __usb_streamlabs_wdt_cmd(STOP) to stop the watchdog; > > > and do not unlock the mutex; > > > > > > in post_reset(): > > > if (watchdog_active()) > > > __usb_streamlabs_wdt_cmd(START); > > > mutex_unlock() to allow other's I/O to the usb deivce. > > > > > > Seems right? > > > > > Not necessarily. Is other code doing something similar ? > > Using a mutex like this creates the risk for hung tasks. > > Are mutexes intended to be used in situations where one function > acquires the lock, then returns, and then a different function releases > the lock? I'm not sure about this. > > Perhaps a good old semaphore would be more appropriate. But it's clear > that I/O to the device does need to be mutually exclusive with resets, > one way or another. Thanks for the idea, I'll look into implementing this. Also, just to let you know there are a lot of drivers who do mutex lock in pre_reset and mutex release in post_reset. And there is 16-years old commit 47104b0dd32cec467574822b0dc3517b3de3f0ad Maybe usb skeleton driver could be updated as well. Best regards, Alexey
