Hi Luis,
On 2016-11-07 22:47, Luis R. Rodriguez wrote:
On Thu, Oct 20, 2016 at 09:22:53AM +0200, Marek Szyprowski wrote:
This patch uses recently introduced device dependency links to track the
runtime pm state of the master's device. This way each SYSMMU controller
is set to runtime active only when its master's device is active and can
restore or save its state instead of being activated all the time when
attached to the given master device. This way SYSMMU controllers no longer
prevents respective power domains to be turned off when master's device
is not being used.
Its unclear why you need this based on this commit log -- is this
needed only on platforms that lack ACPI and use device tree ?
Nope, it has nothing to device tree nor ACPI. The dependency is a direct
result of the way the devices operate.
If so
why? If this issue is present also on systems that only use ACPI is
this possibly due to an ACPI firmware bug or the lack of some semantics
in ACPI to express ordering in a better way? If the issue is device
tree related only is this due to the lack of semantics in device tree
to express some more complex dependency ?
The main feature of device links that is used in this patch is enabling
runtime pm dependency between Exynos SYSMMU controller (called it client
device) and the device, for which it implements DMA address translation
(called master device). The assumptions are following:
1. master device driver is completely unaware of the Exynos SYSMMU presence,
IOMMU is transparently hooked up and managed by DMA-mapping framework
2. SYSMMU belongs to the same power domain as it's master device
3. SYSMMU is optional, master device can fully operate without it, with
simple DMA address translation (DMA address == physical address)
4. Master device implements runtime pm, what in turn causes respective
power domain to be turned on/off
5. DMA-mapping and IOMMU frameworks provides no calls to notify SYSMMU
when its master device is performing DMA operations, so SYSMMU has
to be runtime active
6. Currently SYSMMU always sets its runtime pm status to active after
attaching to its master device to ensure proper hardware state. This
prevents power domain to be turned off, even when master device sets
its runtime pm status to suspended.
7. Exynos SYSMMU has to be runtime active at the same time when its
master device is runtime active to it to perform DMA operations and
allow the power domain to be turned off, when master device is
runtime suspended.
8. The terms of device links, Exynos SYSMMU is a 'consumer' and master
device is a 'supplier'.
Has there been any review of the existing similar solutions out there
such as the DRM / audio component framework? Would that help ?
Nope, none of that solution deals with runtime pm.
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
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