Re: [PATCH] driver core: multithreaded device matching with dependency

From: Stefan Richter
Date: Sat Jun 09 2007 - 12:33:19 EST

Huang, Ying wrote:
> Can this mechanism solve the demand of IEEE1394 subsystem effectively?

Probably. I don't know when I will have time to try it.

(BTW, we should actually be able to probe subunits in parallel, however
I suspect that some firmwares will not tolerate this.)

> +/**
> + * device_match_thaw - renable device/driver matching and check all
> + * pending device/driver matching.

This has to be a single line.

> + * @thread: number of threads to do device/driver matching.
> + *
> + * All devices are checked for driver matching, multithreaded

> +EXPORT_SYMBOL_GPL(device_match_freeze);
> +EXPORT_SYMBOL_GPL(device_match_thaw);

I don't know, perhaps names like "device_driver_matching_disable" and
"device_driver_matching_enable" would be more to the point. Or do you
actually "freeze" (i.e. halt) ongoing driver probes?

> Index: linux-2.6.22-rc4/include/linux/device.h
> ===================================================================
> --- linux-2.6.22-rc4.orig/include/linux/device.h 2007-06-08
> 18:26:11.000000000 +0800
> +++ linux-2.6.22-rc4/include/linux/device.h 2007-06-09
> 19:41:03.000000000 +0800
> @@ -413,12 +413,17 @@
> struct klist_node knode_driver;
> struct klist_node knode_bus;
> struct device *parent;
> + struct device *depend;

Is this core-internal now? If not, add a comment what it does and how
it has to be written and read.

I'm curious how this has to be used; perhaps it will turn out that the
whole thing is over-engineered this way. I.e. there might be easier
options like:
- Let subsystems which don't want multithreaded probing at all
disable multithreaded probing globally by a susbsystem flag.
(Or rather, let subsystems which want multithreaded probing
enable it globally by a subsystem flag. IOW make singlethreaded
probing the default. Multithreaded probing has to be tested
thoroughly for each subsystem.)
- Let subsystems which want only partially multithreaded probing
serialize the necessary regions on their own by subsystem-internal

However, this really depends on what the actual cost of dev->depend is.

> struct kobject kobj;
> char bus_id[BUS_ID_SIZE]; /* position on parent bus */
> struct device_type *type;
> unsigned is_registered:1;
> unsigned uevent_suppress:1;
> + unsigned is_matched:1;
> + unsigned is_checking:1;
> + unsigned is_checked:1;
> + unsigned singlethreaded_probe:1;

Ditto here: Which of these belong to the public API? Those flags which
are not private to the core need to be commented.

PS: There is also a kerneldoc format for structs. It also allows to
mark private struct members, i.e. those which do not belong to the API.
See Documentation/kernel-doc-nano-HOWTO.txt.

PPS: Sadly, the whole struct device and some other driver core API
items lack kerneldocs. It's ironic that the deprecated class_device is
the only drivercore struct which comes with a kerneldoc.
Stefan Richter
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