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SubjectRe: [RFC PATCH v3] driver core: hold dev's parent lock when needed
On Tue, May 29, 2018 at 7:34 PM, Martin Liu <liumartin@google.com> wrote:
> SOC have internal I/O buses that can't be proved for devices. The

Perhaps SoC as a common abbr for system-on-chip.

> 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).

described


>
> In commit 'bf74ad5bc417 introduce ("[PATCH] Hold the device's
> parent's lock during probe and remove")'

The formal commit reference doesn't include '' (surrounding quotes)
and words in square brackets (like [PATCH] here).

> to solve USB subsystem
> lock sequence since usb device's characteristic. Thus "soc"

usb or USB ?

> 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 bus_type struct and driver core would lock the parent lock base
> on the flag. For usbsystem, we set this flag in usb relatvie

USB system

USB

relative

> bus_type struct to keep original lock behavior in driver core.
>
> Async probe could have more benefit after this patch.


> - if (dev->parent) /* Needed for USB */
> + if (dev->parent && dev->bus->need_parent_lock)

So, why not to use bus directly like bus->...?

> device_lock(dev->parent);
> device_release_driver(dev);
> - if (dev->parent)
> + if (dev->parent && dev->bus->need_parent_lock)
> device_unlock(dev->parent);

Ditto here and everywhere else in the patch where applicable.

> + .need_parent_lock = 1,
> + .need_parent_lock = 1,
> + .need_parent_lock = 1,

It's boolean, you need to use true or false. Check and fix your code
correspondingly.

> + bool need_parent_lock;

--
With Best Regards,
Andy Shevchenko

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