Hello,
On 2014-12-15 19:19, Laurent Pinchart wrote:
On Monday 15 December 2014 18:13:23 Will Deacon wrote:
On Mon, Dec 15, 2014 at 05:53:48PM +0000, Laurent Pinchart wrote:
On Monday 15 December 2014 17:43:02 Will Deacon wrote:
On Mon, Dec 15, 2014 at 05:27:30PM +0000, Laurent Pinchart wrote:
On Monday 15 December 2014 17:17:00 Will Deacon wrote:
Creating the platform device manually for the IOMMU is indeed
grotty, but I don't really understand why it's needed. Interrupt
controllers, for example, seem to get by without one.
There's several reasons, one of the most compelling ones I can think
of at the moment is runtime PM. IRQ controllers close to the CPU use
CPU PM notifiers instead. Note that IRQ controllers that are further
away from the CPU (such as GPIO-based IRQ controllers) are real
platform devices and use runtime PM.
Ok, that's a good point, but the IOMMU will still probe later anyway,
right?
That depends on the driver implementation, using OF node match an IOMMU
driver doesn't have to register a struct driver. Assuming we require
IOMMU drivers to register a struct driver, a platform device should then
be probed at a later time.
However, if we wait until the IOMMU gets probed to initialize runtime PM
and make it functional, we'll be back in square one if the IOMMU gets
probed after the bus master, as the bus master could start issuing bus
requests at probe time with the IOMMU not powered yet.
True, but couldn't the early init code do enough to get the thing
functional? That said, I'm showing my ignorance here as I'm not familiar
with the PM code (and the software models I have for the SMMU clearly don't
implement anything in this regard).
We're reaching the limits of my knowledge as well. If the IOMMU is in a power
domain different than the bus masters the driver would at least need to ensure
that the power domain is turned on, which might be a bit hackish without
runtime PM.
In case of Exynos SoC both IOMMU and master device are in the same power
domain.
During iommu_attach() call driver needs to have power domain enabled,
but power
domain driver is probed from arch_initcall(). I wanted to move power domain
initialization earlier to ensure that it will happen before IOMMU driver
probe,
that not really a problem. Right now it usually works, because power
domains are
enabled by bootloader.
However please not that I would really like to have something merged. The
discussion about iommu controllers lasts for about 2 years and we still
don't
have ANYTHING working in mainline, so lets merge the of_iommu glue and then
check how the remaining issues can be solved.
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
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