Re: [PATCH v9 0/7] Solve postboot supplier cleanup and optimize probe ordering

Frank Rowand
2019-08-16T14:05:13Z

i Greg,

On 8/16/19 2:10 AM, Greg Kroah-Hartman wrote:
> On Thu, Aug 15, 2019 at 08:09:19PM -0700, Frank Rowand wrote:
>> Hi Saravana,
>>
>> On 8/15/19 6:50 PM, Saravana Kannan wrote:
>>> On Fri, Aug 9, 2019 at 10:20 PM Frank Rowand <frowand.list@gmail.com> wrote:
>>>>
>>>> On 8/9/19 10:00 PM, Saravana Kannan wrote:
>>>>> On Fri, Aug 9, 2019 at 7:57 PM Frank Rowand <frowand.list@gmail.com> wrote:
>>>>>>
>>>>>> Hi Saravana,
>>>>>>
>>>>>> On 7/31/19 3:17 PM, Saravana Kannan wrote:
>>>>>>> Add device-links to track functional dependencies between devices
>>>>>>> after they are created (but before they are probed) by looking at
>>>>>>> their common DT bindings like clocks, interconnects, etc.
>>>>>>>
>>>>>>> Having functional dependencies automatically added before the devices
>>>>>>> are probed, provides the following benefits:
>>>>>>>
>>>>>>> - Optimizes device probe order and avoids the useless work of
>>>>>>> attempting probes of devices that will not probe successfully
>>>>>>> (because their suppliers aren't present or haven't probed yet).
>>>>>>>
>>>>>>> For example, in a commonly available mobile SoC, registering just
>>>>>>> one consumer device's driver at an initcall level earlier than the
>>>>>>> supplier device's driver causes 11 failed probe attempts before the
>>>>>>> consumer device probes successfully. This was with a kernel with all
>>>>>>> the drivers statically compiled in. This problem gets a lot worse if
>>>>>>> all the drivers are loaded as modules without direct symbol
>>>>>>> dependencies.
>>>>>>>
>>>>>>> - Supplier devices like clock providers, interconnect providers, etc
>>>>>>> need to keep the resources they provide active and at a particular
>>>>>>> state(s) during boot up even if their current set of consumers don't
>>>>>>> request the resource to be active. This is because the rest of the
>>>>>>> consumers might not have probed yet and turning off the resource
>>>>>>> before all the consumers have probed could lead to a hang or
>>>>>>> undesired user experience.
>>>>>>>
>>>>>>> Some frameworks (Eg: regulator) handle this today by turning off
>>>>>>> "unused" resources at late_initcall_sync and hoping all the devices
>>>>>>> have probed by then. This is not a valid assumption for systems with
>>>>>>> loadable modules. Other frameworks (Eg: clock) just don't handle
>>>>>>> this due to the lack of a clear signal for when they can turn off
>>>>>>> resources. This leads to downstream hacks to handle cases like this
>>>>>>> that can easily be solved in the upstream kernel.
>>>>>>>
>>>>>>> By linking devices before they are probed, we give suppliers a clear
>>>>>>> count of the number of dependent consumers. Once all of the
>>>>>>> consumers are active, the suppliers can turn off the unused
>>>>>>> resources without making assumptions about the number of consumers.
>>>>>>>
>>>>>>> By default we just add device-links to track "driver presence" (probe
>>>>>>> succeeded) of the supplier device. If any other functionality provided
>>>>>>> by device-links are needed, it is left to the consumer/supplier
>>>>>>> devices to change the link when they probe.
>>>>>>>
>>>>>>> v1 -> v2:
>>>>>>> - Drop patch to speed up of_find_device_by_node()
>>>>>>> - Drop depends-on property and use existing bindings
>>>>>>>
>>>>>>> v2 -> v3:
>>>>>>> - Refactor the code to have driver core initiate the linking of devs
>>>>>>> - Have driver core link consumers to supplier before it's probed
>>>>>>> - Add support for drivers to edit the device links before probing
>>>>>>>
>>>>>>> v3 -> v4:
>>>>>>> - Tested edit_links() on system with cyclic dependency. Works.
>>>>>>> - Added some checks to make sure device link isn't attempted from
>>>>>>> parent device node to child device node.
>>>>>>> - Added way to pause/resume sync_state callbacks across
>>>>>>> of_platform_populate().
>>>>>>> - Recursively parse DT node to create device links from parent to
>>>>>>> suppliers of parent and all child nodes.
>>>>>>>
>>>>>>> v4 -> v5:
>>>>>>> - Fixed copy-pasta bugs with linked list handling
>>>>>>> - Walk up the phandle reference till I find an actual device (needed
>>>>>>> for regulators to work)
>>>>>>> - Added support for linking devices from regulator DT bindings
>>>>>>> - Tested the whole series again to make sure cyclic dependencies are
>>>>>>> broken with edit_links() and regulator links are created properly.
>>>>>>>
>>>>>>> v5 -> v6:
>>>>>>> - Split, squashed and reordered some of the patches.
>>>>>>> - Refactored the device linking code to follow the same code pattern for
>>>>>>> any property.
>>>>>>>
>>>>>>> v6 -> v7:
>>>>>>> - No functional changes.
>>>>>>> - Renamed i to index
>>>>>>> - Added comment to clarify not having to check property name for every
>>>>>>> index
>>>>>>> - Added "matched" variable to clarify code. No functional change.
>>>>>>> - Added comments to include/linux/device.h for add_links()
>>>>>>>
>>>>>>> v7 -> v8:
>>>>>>> - Rebased on top of linux-next to handle device link changes in [1]
>>>>>>>
>>>>>>
>>>>>>
>>>>>>> v8 -> v9:
>>>>>>> - Fixed kbuild test bot reported errors (docs and const)
>>>>>>
>>>>>> Some maintainers have strong opinions about whether change logs should be:
>>>>>>
>>>>>> (1) only in patch 0
>>>>>> (2) only in the specific patches that are changed
>>>>>> (3) both in patch 0 and in the specific patches that are changed.
>>>>>>
>>>>>> I can adapt to any of the three styles. But for style "(1)" please
>>>>>> list which specific patch has changed for each item in the change list.
>>>>>>
>>>>>
>>>>> Thanks for the context Frank. I'm okay with (1) or (2) but I'll stick
>>>>> with (1) for this series. Didn't realize there were options (2) and
>>>>> (3). Since you started reviewing from v7, I'll do that in the future
>>>>> updates? Also, I haven't forgotten your emails. Just tied up with
>>>>> something else for a few days. I'll get to your emails next week.
>>>>
>>>> Yes, starting with future updates is fine, no need to redo the v9
>>>> change logs.
>>>>
>>>> No problem on the timing. I figured you were busy or away from the
>>>> internet.
>>>
>>> I'm replying to your comments on the other 3 patches. Okay with a
>>> majority of them. I'll wait for your reply to see where we settle for
>>> some of the points before I send out any patches though.
>>>
>>> For now I'm thinking of sending them as separate clean up patches so
>>> that Greg doesn't have to deal with reverts in his "next" branch. We
>>> can squash them later if we really need to rip out what's in there and
>>> push it again.
>>>
>>> -Saravana
>>>
>>
>> Please do not do separate clean up patches. The series that Greg has is
>> not ready for acceptance and I am going to ask him to revert it as we
>> work through the needed changes.
>>
>> I suspect there will be at least two more versions of the series. The
>> first is to get the patches I commented in good shape. Then I will
>> look at the patches later in the series to see how they fit into the
>> big picture.
>>
>> In the end, there should be one coherent patch series that implements
>> the feature.
>
> Incremental patches to fix up the comments and documentation is fine, no
> need to respin the whole mess.

The problem is that the whole thing is a "mess" at this point. I expect
the series to go through at least two or three more versions.

Please revert the series for now.

-Frank

>
> thanks,
>
> greg k-h
>