[RFC PATCH 3/7] iommu/arm-smmu-v3: Introduce smmu option USE_SHARED_IRQS for Silicon errata

[Robin Murphy]

On 11/04/17 17:21, Will Deacon wrote:
> On Tue, Apr 11, 2017 at 04:54:26PM +0100, Robin Murphy wrote:
>> On 11/04/17 15:42, linucherian at gmail.com wrote:
>>> From: Geetha <gakula at cavium.com>
>>>
>>> Cavium 99xx SMMU implementation doesn't not support unique irq lines for
>>> gerror, eventq and cmdq-sync. USE_SHARED_IRQS option enables to use single
>>> irq line for all three interrupts.
>>
>> AFAICS, there's nothing actually wrong with using shared wired IRQs -
>> the architecture spec doesn't appear to say anything about it. I think
>> it might suffice to simply add IRQF_SHARED if we can see the SMMU
>> doesn't support MSIs anyway - it doesn't really seem like something we
>> need to treat as a specific quirk.
> 
> No, this is not permitted by the spec. See 3.18.2 ("Interrupt sources"),
> where it's clear that each source asserts a *unique* wired interrupt.

Perhaps I'm reading it too generously; it does indeed specify that the
*implementation* has to provide a unique output for each source, but
other than suggesting a particular mode of operation based on that I
don't see anything actually forbidding the *integration* from then just
munging those lines together externally, as integrators so often like to
do. That's the case I had in mind.

Robin.

> 
> Geetha: does your implementation support MSIs?
> 
> Will
>