linux-kernel - Re: [PATCH v5] watchdog: add driver for StreamLabs USB watchdog device

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Date:   Sun, 31 Jul 2022 03:34:16 +0100
From:   Alexey Klimov <klimov.linux@...il.com>
To:     Oliver Neukum <oneukum@...e.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        linux-watchdog@...r.kernel.org, wim@...ux-watchdog.org,
        Guenter Roeck <linux@...ck-us.net>,
        USB list <linux-usb@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        atishp@...osinc.com, atishp@...shpatra.org,
        Yury Norov <yury.norov@...il.com>,
        Alexey Klimov <aklimov@...hat.com>,
        Aaron Tomlin <atomlin@...hat.com>
Subject: Re: [PATCH v5] watchdog: add driver for StreamLabs USB watchdog device

On Tue, Jul 26, 2022 at 8:48 AM Oliver Neukum <oneukum@...e.com> wrote:
>
> On 26.07.22 02:21, Alexey Klimov wrote:
> > On Mon, Jul 25, 2022 at 9:51 AM Greg KH <gregkh@...uxfoundation.org> 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@...uxfoundation.org>
> >
> > 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?

Best regards,
Alexey