linux-kernel - Re: [RFC PATCH v2] driver core: hold dev's parent lock when needed

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Message-ID: <CAHp75VejjrmZhEbvV3DEJ88PGnncySdTaWDPFA8Ba5hBy6rmpQ@mail.gmail.com>
Date:   Tue, 29 May 2018 18:28:25 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     martin_liu <liumartin@...gle.com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        "Krogerus, Heikki" <heikki.krogerus@...ux.intel.com>,
        Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        USB <linux-usb@...r.kernel.org>, jenhaochen@...gle.com
Subject: Re: [RFC PATCH v2] driver core: hold dev's parent lock when needed

On Tue, May 29, 2018 at 10:07 AM, martin_liu <liumartin@...gle.com> wrote:
> SOC have internal I/O buses that can't be proved for devices. The
> devices on the buses can be accessed directly without additinal
> configuration required. This type of bus is represented as
> "simple-bus". In some platforms, we name "soc" with "simple-bus"
> attribute and many devices are hooked under it desribed in DT
> (device tree).
>
> In commit 'bf74ad5bc417 introduce ("[PATCH] Hold the device's
> parent's lock during probe and remove")' to solve USB subsystem
> lock sequence since usb device's characteristic. Thus "soc"
> needs to be locked whenever a device and driver's probing
> happen under "soc" bus. During this period, an async driver
> tries to probe a device which is under the "soc" bus would be
> blocked until previous driver finish the probing and release "soc"
> lock. And the next probing under the "soc" bus need to wait for
> async finish. Because of that, driver's async probe for init
> time improvement will be shadowed.
>
> Since many devices don't have USB devices' characteristic, they
> actually don't need parent's lock. Thus, we introduce a lock flag
> in device struct and driver core would lock the parent lock base
> on the flag. For usbsystem, we set this flag when its device and
> driver is matched and to keep original lock behavior in driver
> core.
>
> Async probe could have more benefit after this patch.

> Signed-off-by: martin_liu <liumartin@...gle.com>

Strange Firstname Lastname format...

> Suggested-by: Alan Stern <stern@...land.harvard.edu>

I guess your SoB should go last (at least this is how -s works in git commit)

>         /* Some ULPI devices don't have a vendor id so rely on OF match */
> -       if (ulpi->id.vendor == 0)
> -               return of_driver_match_device(dev, driver);
> +       if (ulpi->id.vendor == 0) {
> +               if (of_driver_match_device(dev, driver)) {
> +                       dev->need_parent_lock = 1;
> +                       return 1;
> +               }

> +               return o;

Return what?

> +       }

-- 
With Best Regards,
Andy Shevchenko