Hi,
On 13-01-17 17:30, Ville Syrjälä wrote:
On Fri, Jan 13, 2017 at 05:06:52PM +0100, Hans de Goede wrote:
Hi,
On 01/13/2017 10:26 AM, Ville Syrjälä wrote:
On Mon, Jan 02, 2017 at 03:21:13PM +0100, Hans de Goede wrote:
Hi,
On 02-01-17 15:12, Ville Syrjälä wrote:
On Sun, Jan 01, 2017 at 09:14:00PM +0100, Hans de Goede wrote:
The punit on baytrail / cherrytrail systems is not only accessed through
the iosf_mbi functions, but also by the i915 code. Add a mutex to protect
the punit against simultaneous accesses and 2 functions to lock / unlock
this mutex.
I'm not sure which part of punit you're actually trying to protect
here. Some specific registers?
The theory I'm going by is that for certain actions / certain requests
we send to the punit, the punit needs to access the (axp288) pmic, to
change (or enable / disable) certain voltages.
At least for cpu/display/gt voltages that shouldn't really be the case.
The vcc/vnn/vgg rails are controlled via svid, not i2c.
Are you sure? The ax288 pmic does not have a svid interface, only
an i2c interface, and AFAICT its buck DCDC converters are used to
feed all of these.
Yes, looks like you're right. I guess someone didn't want to spend three
pins for svid.
It also feels quite hand wavy since the punit could do whatever at
any time AFAIK. Eg. if there's some thermal event or something the
punit might kick into action. So trying to protect this from the OS
side might not be able to avoid these problems entirely. It feels like
there really should be some kind of shared hardware/firmware mutex
with the punit to arbitrate access to the i2c bus.
Right, and there is such a mutex (which only gets used on systems
with an axp288 pmic...) and we are taking this mutex before starting
an i2c transaction on the pmic i2c bus. But this does not seem to be
enough. It seems the the punit does not check the mutex before
certain OS / host triggered actions. I guess it expects the host to
do this itself.
Please see my new (non RFC) version of this series I've posted.
There are at least 2 problems when relying solely on the punit
pmic i2c bus sempaphore:
1) CPU C1 <-> C6 transations happening while the pmic i2c bus
is being accessed by the host cause the system to hang
2) i915 (runtime) suspend resume fails every other attempt
with timeouts when trying to get a forcewake lock inn i915,
often followed by a system freeze shortly after this.
Hmm. But forcewake works at other times?
It depends on the workload, I believe the forcewake timeouts are
caused by e.g. the axp288 fuel-gauge driver directly accessing
the pmic i2c bus at the same time as the i915 driver is doing a
forcewake. So in essence this is race and as such not 100%
reproducible. With my workload (Fedora 25 with gnome3) full suspend
+ resume is a good way to reproduce. The bug reporter
(tagorereddy) in:
https://bugzilla.kernel.org/show_bug.cgi?id=155241
Is seeing this during normal use when using a kde / plasma desktop.
Some history, this problem started surfacing when I fixed the
i2c punit semaphore code in i2c-designware-baytrail.c to actually
work on cht, before that systems with an axp288 any attempt to
access the i2c bus by e.g. the axp288_fuel_gauge driver would result
in -ETIMEOUT as the code would fail to acquire the punit i2c bus
semaphore, this i2c-designware-baytrail.c cht bug has so far protected
users against the described race (*).
tagorereddy then tried my patches to get battery monitoring working
on his cht device. Then he reported back in the above bug that he
was getting forcewake timeouts + system hangs. I only noticed I could
reproduce them myself on resume later (which was quite useful in
actually developing the proposed fix).
> That seems quite strange.
Runtime suspend itself shouldn't really do much, and if we're still
poking at the the hw then we haven't really even suspended anything
yet, so having failing forcewake doesn't sounds at all good.
Sorry, I'm actually seeing these on a (full not runtime) resume,
not suspend, it seems that at resume my setup has the ideal
circumstances to hit the race.
Regards,
Hans
*) Note as described in the cover letter of the non RFC version of
this patch-set:
https://www.spinics.net/lists/dri-devel/msg128896.html
Disabling access to the pmic i2c bus (as the fixed bug does) is
not a workable solution:
"Unfortunately that will cause some major issues on affected devices:
-No battery monitoring
-No "AC" plugged in monitoring
-If booted with a normal USB-A -> micro-USB cable, or no cable, plugged
in and then the user replaces the cable with an otg USB-host cable /
adapter, the id-pin shorting will enable a 5v boost convertor, but we
need to disable the pmic's USB-Vbus path otherwise it will start drawing
current from the boost convertor, leading to aprox 300mA of extra
battery drain, this is done by the axp288_charger driver, which needs
direct i2c access to the pmic bus"
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