Re: [PATCH v9 06/10] ata: zpodd: check zero power ready status

[Aaron Lu <aaron.lu@intel.com>]

On 11/26/2012 09:03 AM, Rafael J. Wysocki wrote:
> On Monday, November 26, 2012 08:48:51 AM Aaron Lu wrote:
>> On 11/26/2012 08:50 AM, Rafael J. Wysocki wrote:
>>> On Tuesday, November 20, 2012 04:59:57 PM Aaron Lu wrote:
>>>> On 11/20/2012 02:00 PM, Aaron Lu wrote:
>>>>> On 11/19/2012 10:56 PM, Tejun Heo wrote:
>>>>>> I really think we need a way for (auto)pm and event polling to talk to
>>>>>> each other so that autopm can tell event poll to sod off while pm is
>>>>>> in effect.  Trying to solve this from inside libata doesn't seem
>>>>>> right.  The problem, again, seems to be figuring out which hardware
>>>>>> device maps to which block device.  Hmmm... Any good ideas?
>>>>>
>>>>> A possible way of doing this is using pm qos.
>>>>>
>>>>> We currently have 2 pm qos flags, NO_POWER_OFF and REMOTE_WAKEUP, and we
>>>>> can add another one: NO_POLL, use it like the following:
>>>>> 1 Set the NO_POLL pm qos flag when the underlying driver thinks it is no
>>>>>   longer necessary. In the ZPODD's case, it should be set when the
>>>>>   device is to be powered off;
>>>>> 2 Clear it when poll is necessary again. In the ZPODD's case, when power
>>>>>   is re-gained, this flag will be cleared.
>>>>
>>>>
>>>>> 3 In the disk_events_workfn, check if this flag is set, if so, simply
>>>>>   return.
>>>>
>>>> It should be, skip calling disk->fops->check_events, but still queue the
>>>> work for next time's poll.
>>>>
>>>> -Aaron
>>>>
>>>>>
>>>>> The disk->driverfs_dev can be used to host the pm qos flag, ATA layer
>>>>> can access it through ata_device->sdev->sdev_gendev.
>>>>>
>>>>> Is this OK?
>>>
>>> No, I don't think so.  PM QoS is about telling the layer that will put the
>>> device into low-power states what states are to be taken into consideration.
>>> In this case, however, we need to tell someone else that the device has been
>>> turned off.  Clearly, we need a way to do that, but not through PM QoS.
>>>
>>> Did you consider using pm_runtime_suspended() to check the device status?
>>
>> The problem is, a device can be in runtime suspended state while still
>> needs to be polled...
> 
> Well, maybe this is the problem, then?  Why does it need to be polled when
> suspended?

For ODDs, poll is not necessary only when ZP capable ODD is powered off.
For other ODDs, poll still needs to go on.

ZP capable ODDs:
  - runtime suspended, power remained(due to NO_POWER_OFF qos flag)
    poll is needed
  -- runtime suspended, power removed
    poll is not needed

Non ZP capable ODDs:
  -- runtime suspended, power remained (power will never be removed)
    poll is needed

If we do not poll for the powered on case, we will lose media change
event.

Thanks,
Aaron

> 
> Rafael
> 
>