Re: [PATCH] i2c: designware: platdrv: Remove DPM_FLAG_SMART_SUSPEND flag on BYT and CHT

[Jarkko Nikula <jarkko.nikula@linux.intel.com>]

On 4/7/20 10:30 PM, Rafael J. Wysocki wrote:
> On Tue, Apr 7, 2020 at 8:11 PM Hans de Goede <hdegoede@redhat.com> wrote:
>>
>> We already set DPM_FLAG_SMART_PREPARE, so we completely skip all
>> callbacks (other then prepare) where possible, quoting from
>> dw_i2c_plat_prepare():
>>
>>          /*
>>           * If the ACPI companion device object is present for this device, it
>>           * may be accessed during suspend and resume of other devices via I2C
>>           * operation regions, so tell the PM core and middle layers to avoid
>>           * skipping system suspend/resume callbacks for it in that case.
>>           */
>>          return !has_acpi_companion(dev);
>>
>> Also setting the DPM_FLAG_SMART_SUSPEND will cause acpi_subsys_suspend()
>> to leave the controller runtime-suspended even if dw_i2c_plat_prepare()
>> returned 0.
>>
>> Leaving the controller runtime-suspended normally, when the I2C controller
>> is suspended during the suspend_late phase, is not an issue because
>> the pm_runtime_get_sync() done by i2c_dw_xfer() will (runtime-)resume it.
>>
>> But for dw I2C controllers on Bay- and Cherry-Trail devices acpi_lpss.c
>> leaves the controller alive until the suspend_noirq phase, because it may
>> be used by the _PS3 ACPI methods of PCI devices and PCI devices are left
>> powered on until the suspend_noirq phase.
>>
>> Between the suspend_late and resume_early phases runtime-pm is disabled.
>> So for any ACPI I2C OPRegion accesses done after the suspend_late phase,
>> the pm_runtime_get_sync() done by i2c_dw_xfer() is a no-op and the
>> controller is left runtime-suspended.
>>
>> i2c_dw_xfer() has a check to catch this condition (rather then waiting
>> for the I2C transfer to timeout because the controller is suspended).
>> acpi_subsys_suspend() leaving the controller runtime-suspended in
>> combination with an ACPI I2C OPRegion access done after the suspend_late
>> phase triggers this check, leading to the following error being logged
>> on a Bay Trail based Lenovo Thinkpad 8 tablet:
>>
>> [   93.275882] i2c_designware 80860F41:00: Transfer while suspended
>> [   93.275993] WARNING: CPU: 0 PID: 412 at drivers/i2c/busses/i2c-designware-master.c:429 i2c_dw_xfer+0x239/0x280
>> ...
>> [   93.276252] Workqueue: kacpi_notify acpi_os_execute_deferred
>> [   93.276267] RIP: 0010:i2c_dw_xfer+0x239/0x280
>> ...
>> [   93.276340] Call Trace:
>> [   93.276366]  __i2c_transfer+0x121/0x520
>> [   93.276379]  i2c_transfer+0x4c/0x100
>> [   93.276392]  i2c_acpi_space_handler+0x219/0x510
>> [   93.276408]  ? up+0x40/0x60
>> [   93.276419]  ? i2c_acpi_notify+0x130/0x130
>> [   93.276433]  acpi_ev_address_space_dispatch+0x1e1/0x252
>> ...
>>
>> So since on BYT and CHT platforms we want ACPI I2c OPRegion accesses
>> to work until the suspend_noirq phase, we need the controller to be
>> runtime-resumed during the suspend phase if it is runtime-suspended
>> suspended at that time. This means that we must not set the
>> DPM_FLAG_SMART_SUSPEND on these platforms.
>>
>> On BYT and CHT we already have a special ACCESS_NO_IRQ_SUSPEND flag
>> to make sure the controller stays functional until the suspend_noirq
>> phase. This commit makes the driver not set the DPM_FLAG_SMART_SUSPEND
>> flag when that flag is set.
> 
> OK
> 
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>