linux-kernel - Re: [PATCH 2/3] scsi: add hooks for host runtime power management

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Date:	Thu, 03 Nov 2011 22:37:43 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Jeff Garzik <jgarzik@...ox.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	James Bottomley <JBottomley@...allels.com>,
	Tejun Heo <tj@...nel.org>,
	"Huang, Ying" <ying.huang@...el.com>,
	"Zhang, Rui" <rui.zhang@...el.com>
Subject: Re: [PATCH 2/3] scsi: add hooks for host runtime power management

On Thu, 2011-11-03 at 22:22 +0800, Alan Stern wrote:
> On Thu, 3 Nov 2011, Lin Ming wrote:
> 
> > I realize that this is not the natural way to do ata port runtime pm.
> > Hooking it to scsi host runtime pm is not good. It does not deal with
> > the races with system suspend/resume of host controller.
> > 
> > How about making ata port as the parent device of scsi host?
> > Then, for example, the runtime suspend happens as below,
> > 
> > disk suspend --> scsi target suspend --> scsi host suspend --> ata port
> > suspend.
> > 
> > Current device tree is:
> > /sys/devices/pci0000:00/0000:00:1f.2/
> > |-- ata1
> > |-- host0
> > 
> > After the change, the tree will become as:
> > /sys/devices/pci0000:00/0000:00:1f.2/ata1/
> > |-- host0
> 
> I don't know enough about the ATA subsystem to say much, except that 
> this looks more logical.
> 
> > The tricky part is ata port(parent device) suspend need to schedule scsi
> > EH which will resume scsi host(child device). Then the child device
> > resume will in turn make parent device resume first. This is kind of
> > recursive.
> > 
> > We can fix this by adding a flag somewhere to tell scsi EH don't resume
> > the host in ata port pm request handling case.
> > 
> > What do you think?
> 
> Yes, it is a problem.  But it looks like the underlying issue is that
> you're using the SCSI error handler to do something it was not intended
> for.  Can't you suspend and resume the ATA port without using the error
> handler?

The system suspend and resume of the ATA port uses the error handler.
I think the runtime suspend and resume should use the error handler too.

Tejun,

Could you comment more on this?

Thanks.

> 
> Alan Stern
> 


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