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This patch (as1520) fixes a bug in the SCSI layer's power management
implementation.
LUN scanning can be carried out asynchronously in do_scan_async(), and
sd uses an asynchronous thread for the time-consuming parts of disk
probing in sd_probe_async(). Currently nothing coordinates these
async threads with system sleep transitions; they can and do attempt
to continue scanning/probing SCSI devices even after the host adapter
has been suspended. As one might expect, the outcome is not ideal.
This is what the "prepare" stage of system suspend was created for.
After the prepare callback has been called for a host, target, or
device, drivers are not allowed to register any children underneath
them. Currently the SCSI prepare callback is not implemented; this
patch rectifies that omission.
For SCSI hosts, the prepare routine calls scsi_complete_async_scans()
to wait until async scanning is finished. It might be slightly more
efficient to wait only until the host in question has been scanned,
but there's currently no way to do that. Besides, during a sleep
transition we will ultimately have to wait until all the host scanning
has finished anyway.
For SCSI devices, the prepare routine calls async_synchronize_full()
to wait until sd probing is finished. The routine does nothing for
SCSI targets, because asynchronous target scanning is done only as
part of host scanning.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: <stable@kernel.org>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
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[Patch description from Alan Stern]
If a child device was runtime-suspended when a system suspend began,
then there will be nothing to prevent its parent from
runtime-suspending as soon as it is woken up during the system resume.
Then when the time comes to resume the child, the resume will fail
because the parent is already back at low power.
On the other hand, there are some devices which should remain at low
power across an entire suspend-resume cycle. The details depend on the
device and the platform.
This suggests that the PM core is not the right place to solve the
problem. One possible solution is for the subsystem or device driver
to call pm_runtime_get_sync(dev->parent) at the start of the
system-resume procedure and pm_runtime_put_sync(dev->parent) at the
end.
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
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The only high-level SCSI driver that currently implements runtime PM is
sd, and sd treats runtime suspend exactly the same as the SUSPEND and
HIBERNATE stages of system sleep, but not the same as the FREEZE stage.
Therefore, when entering the SUSPEND or HIBERNATE stages of system
sleep, we can skip the callback to the driver if the device is already
in runtime suspend. When entering the FREEZE stage, however, we should
first issue a runtime resume. The overhead of doing this is
negligible, because a suspended drive would be spun up during the THAW
stage of hibernation anyway.
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
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For the basic SCSI infrastructure files that are exporting symbols
but not modules themselves, add in the basic export.h header file
to allow the exports.
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
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Some callers of pm_runtime_get_sync() and other runtime PM helper
functions, scsi_autopm_get_host() and scsi_autopm_get_device() in
particular, need to distinguish error codes returned when runtime PM
is disabled (i.e. power.disable_depth is nonzero for the given
device) from error codes returned in other situations. For this
reason, make the runtime PM helper functions return -EACCES when
power.disable_depth is nonzero and ensure that this error code
won't be returned by them in any other circumstances. Modify
scsi_autopm_get_host() and scsi_autopm_get_device() to check the
error code returned by pm_runtime_get_sync() and ignore -EACCES.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
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This patch (as1398b) adds runtime PM support to the SCSI layer. Only
the machanism is provided; use of it is up to the various high-level
drivers, and the patch doesn't change any of them. Except for sg --
the patch expicitly prevents a device from being runtime-suspended
while its sg device file is open.
The implementation is simplistic. In general, hosts and targets are
automatically suspended when all their children are asleep, but for
them the runtime-suspend code doesn't actually do anything. (A host's
runtime PM status is propagated up the device tree, though, so a
runtime-PM-aware lower-level driver could power down the host adapter
hardware at the appropriate times.) There are comments indicating
where a transport class might be notified or some other hooks added.
LUNs are runtime-suspended by calling the drivers' existing suspend
handlers (and likewise for runtime-resume). Somewhat arbitrarily, the
implementation delays for 100 ms before suspending an eligible LUN.
This is because there typically are occasions during bootup when the
same device file is opened and closed several times in quick
succession.
The way this all works is that the SCSI core increments a device's
PM-usage count when it is registered. If a high-level driver does
nothing then the device will not be eligible for runtime-suspend
because of the elevated usage count. If a high-level driver wants to
use runtime PM then it can call scsi_autopm_put_device() in its probe
routine to decrement the usage count and scsi_autopm_get_device() in
its remove routine to restore the original count.
Hosts, targets, and LUNs are not suspended while they are being probed
or removed, or while the error handler is running. In fact, a fairly
large part of the patch consists of code to make sure that things
aren't suspended at such times.
[jejb: fix up compile issues in PM config variations]
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>
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This patch (as1397b) converts the SCSI midlayer to use the new PM
callbacks (struct dev_pm_ops). A new source file, scsi_pm.c, is
created to hold the new callback routines, and the existing
suspend/resume code is moved there.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>
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