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

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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?

Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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