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authorMartin Liu <liumartin@google.com>2018-05-31 00:31:36 +0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-05-31 10:12:07 +0200
commit8c97a46af04b4f7c0a0dded031fef1806872e648 (patch)
tree5405b6d743493ce9fc0ab0a411573531ab33eef3 /fs/kernfs
parent0dda2bb6242361afd68332bf19bd67cd5981eb26 (diff)
downloadlinux-8c97a46af04b4f7c0a0dded031fef1806872e648.tar.bz2
driver core: hold dev's parent lock when needed
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 described in DT (device tree). In commit bf74ad5bc417 ("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 bus_type struct and driver core would lock the parent lock base on the flag. For USB, we set this flag in usb_bus_type to keep original lock behavior in driver core. Async probe could have more benefit after this patch. Signed-off-by: Martin Liu <liumartin@google.com> Acked-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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