[PATCH/RFC 0/4] Probe deferral for IOMMU DT integration

Laura Abbott lauraa at codeaurora.org
Mon Feb 9 13:27:58 PST 2015

On 2/7/2015 2:41 PM, arnd at arndb.de wrote:
> Laura Abbott <lauraa at codeaurora.org> hat am 6. Februar 2015 um 01:31
> geschrieben:
>> The requirement for this is based on a previous patch to add clock
>> support to the ARM SMMU driver[2]. Once we have clock support, it's
>> possible that the driver itself may need to be defered which breaks
>> a bunch of assumptions about how SMMU probing is supposed to work.
> Hi Laura,
> I was hoping that we would not need this, and instead treat the iommu in
> the same way as timers and SMP initialization, both
> of which need to be run early at boot time but may rely on clock controllers
> to be initialized first.
> Is there a specific requirement that makes this impossible here, or is your
> intention to solve the problem more nicely by allowing deferred probing
> over forcing the input clocks of the iommu to be early?
>        Arnd

The current clock driver for qcom targets doesn't support the early
initialization needed for timers and SMP because neither of those depend
on the clocksources. I discussed this with Stephen some and adding the
early support would not mesh well with the device/driver design of the
current clock driver so that's not really an option right now.

I do think the deferred probing design is cleaner. Even cleaner would
be a proper bus type but that's a different can of worms.


Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

More information about the linux-arm-kernel mailing list