[PATCH v4 1/2] drivers: bus: simple-pm-bus: Add support for probing simple bus only devices

[Kevin Hilman]

Saravana Kannan <saravanak at google.com> writes:

> On Mon, Jan 31, 2022 at 7:18 PM Kevin Hilman <khilman at baylibre.com> wrote:
>>
>> Hi Saravana,
>>
>> Saravana Kannan <saravanak at google.com> writes:
>>
>> > fw_devlink could end up creating device links for bus only devices.
>> > However, bus only devices don't get probed and can block probe() or
>> > sync_state() [1] call backs of other devices. To avoid this, probe these
>> > devices using the simple-pm-bus driver.
>> >
>> > However, there are instances of devices that are not simple buses (they get
>> > probed by their specific drivers) that also list the "simple-bus" (or other
>> > bus only compatible strings) in their compatible property to automatically
>> > populate their child devices. We still want these devices to get probed by
>> > their specific drivers. So, we make sure this driver only probes devices
>> > that are only buses.
>> >
>> > [1] - https://lore.kernel.org/lkml/CAPDyKFo9Bxremkb1dDrr4OcXSpE0keVze94Cm=zrkOVxHHxBmQ@mail.gmail.com/
>> > Fixes: c442a0d18744 ("driver core: Set fw_devlink to "permissive" behavior by default")
>> > Signed-off-by: Saravana Kannan <saravanak at google.com>
>> > Tested-by: Saravana Kannan <saravanak at google.com>
>> > Tested-by: Ulf Hansson <ulf.hansson at linaro.org>
>>
>> This patch landed in stable/linux-5.10.y as commit d5f13bbb5104 and it
>> broke suspend/resume on at least one TI AM335x board I'm testing on:
>> upstream dts: arch/arm/boot/dts/am335x-icev2.dts, upstream defconfig:
>> arch/arm/configs/omap2plus_defconfig.
>>
>> Bisecting between vanilla v5.10 (good) and stable/linux-5.10.y (bad)
>> pointed me to this patch, and I confirmed that reverting just this patch
>> on top of stable/linux-5.10.y makes it work again.
>>
>> Also interesting, this same platform works fine on vanilla v5.15, which
>> also includes this patch.  That suggests that either 1) this patch
>> should not have been backported to v5.10 stable or 2) there are some
>> other dependencies that are missing in v5.10.
>>
>> Since vanilla v5.10 works fine, I'm leaning towards (1), but if you have
>> any ideas for deps that need backporting, I'm happy to try.
>
> Oh wow! I didn't realize I made so many changes AFTER 5.10! Unless I'm
> doing something wrong with my git commands.
> $ git log v5.10..v5.15 --oneline -- drivers/of/property.c
> $ git log v5.10..v5.15 --oneline --author=saravanak -- drivers/base/
>
> If you don't think I got my git command completely wrong, yeah, way
> too many patches are missing on 5.10. I'd go with the option of
> dropping this patch on 5.10.

I agree.  Could you submit a revert for v5.10 stable?  As the patch
author, it's probably better if it comes from you.

>> I haven't debugged exactly where it's hanging yet, but, enabling
>> CONFIG_DEBUG_DRIVER=y, and suspending with "no_console_suspend" on the
>> command line, the last line before it hangs is:
>>
>>    [   28.129966] simple-pm-bus ocp: noirq power domain suspend
>>
>> Any ideas?
>
> I'd guess it's either a sync_state() happening too soon since some of
> the dependencies aren't tracked. Or some dependency cycle that'd be
> handled correctly if the rest of the patches were picked up. Yeah, a
> pretty broad/vague answer.

Heh, yeah, and also suggests that there's other gotchas hiding in other
dark corners, which also suggests that revert is the best path for
v5.10.

Thanks for the quick response,

Kevin