Date:   Fri, 16 Sep 2016 09:57:10 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM list <linux-pm@...r.kernel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Mark Brown <broonie@...nel.org>,
        Lukas Wunner <lukas@...ner.de>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        "Luis R. Rodriguez" <mcgrof@...e.com>
Subject: Re: [RFC/RFT][PATCH v3 0/5] Functional dependencies between devices

Hi Everyone,

On 2016-09-16 09:25, Marek Szyprowski wrote:
> 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 outdated now).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
>>> patches.
>>>
>>> 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'
>> comments.
>>
>> 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
>> them.
>>
>> 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.
>

The issue was caused by missing braces in device_links_no_driver() 
function.
After fixing it the patches works fine, so you can add:

Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

Rafael, how and when do you plan to merge them? I would like to know how to
process further with my IOMMU patch, which is depends on your patches.

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

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