[PATCH v6 1/8] iommu: provide early initialisation hook for IOMMU drivers

Grant Likely
2014-12-05T13:21:31Z

On Fri, Dec 5, 2014 at 1:18 PM, Thierry Reding <thierry.reding@gmail.com> wrote:
> On Fri, Dec 05, 2014 at 01:06:52PM +0000, Grant Likely wrote:
>> On Fri, Dec 5, 2014 at 12:35 PM, Robin Murphy <robin.murphy@arm.com> wrote:
>> > Hi Will,
>> >
>> > On 05/12/14 12:10, Will Deacon wrote:
>> > [...]
>> >>>>
>> >>>> Do you expect drivers to modify that *priv pointer after the ops
>> >>>> structure is registered? I'd be very surprised if that was the use
>> >>>> case. It's fine for the driver to register a non-const version, but
>> >>>> once it is registered, the infrastructure can treat it as const from
>> >>>> then on.
>> >>>
>> >>>
>> >>> Possibly not - certainly my current port of the ARM SMMU which makes use
>> >>> of *priv is only ever reading it - although we did also wave around
>> >>> reasons for mutable ops like dynamically changing the pgsize_bitmap and
>> >>> possibly even swizzling individual ops for runtime reconfiguration. On
>> >>> consideration though, I'd agree that things like that are mad enough to
>> >>> stay well within individual drivers if they did ever happen, and
>> >>> certainly shouldn't apply to this bit of the infrastructure at any rate.
>> >>
>> >>
>> >> I certainly need to update the pgsize_bitmap at runtime because I don't
>> >> know the supported page sizes until I've both (a) probed the hardware
>> >> and (b) allocated page tables for a domain. We've already discussed
>> >> moving the pgsize_bitmap out of the ops, but moving it somewhere where
>> >> it remains const doesn't really help.
>> >
>> >
>> > We can safely cast the call to get_ops in the SMMU driver though, since
>> > we'll know that we put a mutable per-instance ops in there in the first
>> > place. At least that way drivers that aren't taking advantage and just pass
>> > their static const ops around shouldn't provoke warnings. I deliberately
>> > didn't touch anything beyond get_ops as that would be too disruptive.
>> >
>> >> Can I just take the patch that Grant acked, in the interest of getting
>> >> something merged? As you say, there's plenty of planned changes in this
>> >> area anyway. I plan to send Olof a pull request this afternoon.
>> >
>> >
>> > Grant, Thierry? Personally I'm not fussed either way - the sooner something
>> > goes in, the sooner I can carry on working at replacing it :D
>>
>> I've already acked it. Why are we still talking about it? :-D
>
> Am I missing something? Why is there a need to rush things? Are there
> actually drivers that depend on this that will be merged during the 3.19
> merge window? It seems like that'd be cutting it really close given
> where we are in the release cycle.
>
> If that's not the case, why even bother getting this hack into 3.19 if
> nobody uses it and we're going to change it in 3.20 anyway?

I also acked the non-hack version, the patch that doesn't try to make
everything const. I assumed that was the one that we are talking about
merging.

g.