[PATCH 0/3] PM: Make it possible to expose PM QoS latency constraints

["Rafael J. Wysocki" <rjw@sisk.pl>]

Hi all,

On Sunday, March 04, 2012, Rafael J. Wysocki wrote:
> On Sunday, March 04, 2012, Rafael J. Wysocki wrote:
> > 
> > The goal of this patchset is to allow user space to control the
> > responsiveness of the MMC stack related to runtime power management.
> > 
> > Namely, on systems that contain power domains, the time necessary
> > to bring an MMC host up after it has been runtime-suspended may
> > depend not only on the MMC core and host driver, but also on the platform
> > and other devices in the same power domain(s) that contain(s) the MMC
> > host.  Although that obviously may influence the MMC performance,
> > currently, there is no way to control it through the MMC subsystem.
> > Moreover, the only available way to control it at all is by using PM QoS
> > latency requests, so it is necessary to add some kind of support for that
> > to MMC.
> > 
> > Patch [1/3] adds PM QoS-related fields to struct mmc_host and introduces
> > a new sysfs attribute for MMC hosts, pm_latency_limit_ms, allowing user
> > space to influence the MMC host's runtime PM via PM QoS.  Whether or not
> > this attribute will be created (and PM QoS will be used for the given host)
> > depends on the host driver, so host drivers that don't (plan) to support
> > PM QoS don't need to do anything about that.
> > 
> > Patches [2/3] and [3/3] add the corresponding host driver bits to the
> > tmio_mmc and sh_mmcif drivers, respectively.
> 
> After posting the patches I noticed that the changelog of patch [1/3] and
> the documentation of the new sysfs attribute were not 100% accurate, because
> the PM QoS request really applies to the time between a resume request and
> the moment the device is operational again and not the time from runtime
> suspend (the latter would imply some kind of autoresume mechanism, which isn't
> there).
> 
> I also thought it would be cleaner to allocate the val and attr fields along
> with the request, because in the previous version of the patchset they weren't
> used when req was NULL, resulting in (a little) wasted memory.
> 
> Updated patches follow.

Taking the feedback so far into account, I decided to move the exposing of the
PM QoS latency limit from the MMC layer to the PM core sysfs code, so that
every driver (not only MMC host drivers) can use it.

New patches follow, details are in the changelogs:

[1/3] - Make it possible to expose PM QoS latency constraints
[2/3] - Make tmio_mmc use the new interface.
[3/3] - Make sh_mmcif use the new interface.

Thanks,
Rafael