Re: [RFC/RFT][PATCH v3 0/5] Functional dependencies between devices

From: Marek Szyprowski
Date: Fri Sep 16 2016 - 03:26:05 EST

Hi Rafael,

On 2016-09-16 00:03, Rafael J. Wysocki wrote:
Hi Everyone,

On Thursday, September 08, 2016 11:25:44 PM Rafael J. Wysocki wrote:
Hi Everyone,

This is a refresh of the functional dependencies series that I posted last
year and which has picked up by Marek quite recently. For reference, appended
is my introductory message sent previously (which may be slightly outdated now).

As last time, the first patch rearranges the code around __device_release_driver()
a bit to prepare it for the next one (it actually hasn't changed AFAICS).

The second patch introduces the actual device links mechanics, but without
system suspend/resume and runtime PM support which are added by the subsequent

Some bugs found by Marek during his work on these patches should be fixed
here. In particular, the endless recursion in device_reorder_to_tail()
which simply was broken before.

There are two additional patches to address the issue with runtime PM support
that occured when runtime PM was disabled for some suppliers due to a PM
sleep transition in progress. Those patches simply make runtime PM helpers
return 0 in that case which may be controversial, so please let me know if
there are concerns about those.

The way device_link_add() works is a bit different, as it takes an additional
status argument now. That makes it possible to create a link in any state,
with extra care of course, and should address the problem pointed to by Lukas
during the previous discussion.

Also some comments from Tomeu have been addressed.
An update here.

The first patch hasn't changed, so I'm resending it.

The majority of changes in the other patches are in order to address Lukas'

First off, I added a DEVICE_LINK_STATELESS flag that will prevent the driver
core from trying to maintain device links having it set.

Also, the DEVICE_LINK_PERSISTENT flag was dropped (as link "persistence" is the
default behavior now) and there's a new one, DEVICE_LINK_AUTOREMOVE, that will
cause the driver core to remove the link on the consumer driver unbind.

Moreover, the code checks attempts to create a link between a parent and a child
device now and actively prevents that from happening.

The changelog of the second patch has been updated as requested by Ulf.

The third patch was updated to fix a bug related to the (previously missing)
clearing of power.direct_complete for supplier devices having consumers that
don't use direct_complete.

The next two (runtime PM) patches turned out to be unnecessary, so I've dropped

The runtime PM patch [4/5] was reorganized somewhat to reduce the indentation
level in there, but the code flow introduced by it is essentially the same
and the last patch was simply rebased on top of the new series.

If this version still works for Marek, I'll probably drop the RFC tag from it
in the next iteration.

Sadly, this version doesn't work. I get following kernel bug:

[ 2.357622] BUG: spinlock bad magic on CPU#0, swapper/0/1
[ 2.362361] lock: 0xeea2e294, .magic: ffffffff, .owner: /0, .owner_cpu: -1
[ 2.369389] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.8.0-rc6-00019-gd66d0028dd3c-dirty #651
[ 2.377954] Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
[ 2.384053] [<c010d7f0>] (unwind_backtrace) from [<c010a4b4>] (show_stack+0x10/0x14)
[ 2.391766] [<c010a4b4>] (show_stack) from [<c032220c>] (dump_stack+0x74/0x94)
[ 2.398970] [<c032220c>] (dump_stack) from [<c0158e8c>] (do_raw_spin_lock+0x160/0x1a8)
[ 2.406870] [<c0158e8c>] (do_raw_spin_lock) from [<c03e8d84>] (device_links_no_driver+0x64/0x98)
[ 2.415634] [<c03e8d84>] (device_links_no_driver) from [<c03ec32c>] (driver_probe_device+0xa0/0x2bc)
[ 2.424744] [<c03ec32c>] (driver_probe_device) from [<c03ec5f4>] (__driver_attach+0xac/0xb0)
[ 2.433165] [<c03ec5f4>] (__driver_attach) from [<c03eaa90>] (bus_for_each_dev+0x54/0x88)
[ 2.441323] [<c03eaa90>] (bus_for_each_dev) from [<c03eba6c>] (bus_add_driver+0xe8/0x1f4)
[ 2.449481] [<c03eba6c>] (bus_add_driver) from [<c03ece54>] (driver_register+0x78/0xf4)
[ 2.457469] [<c03ece54>] (driver_register) from [<c010178c>] (do_one_initcall+0x3c/0x16c)
[ 2.465632] [<c010178c>] (do_one_initcall) from [<c0b00d84>] (kernel_init_freeable+0x120/0x1ec)
[ 2.474313] [<c0b00d84>] (kernel_init_freeable) from [<c0704194>] (kernel_init+0x8/0x118)
[ 2.482470] [<c0704194>] (kernel_init) from [<c01079b8>] (ret_from_fork+0x14/0x3c)

I'm checking what's wrong there.

Best regards
Marek Szyprowski, PhD
Samsung R&D Institute Poland