[PATCH v2 1/4] genirq/irqdomain: Allow partial trimming of irq_data hierarchy
Marc Zyngier
maz at kernel.org
Wed Oct 7 08:23:58 EDT 2020
On 2020-10-07 09:53, Marc Zyngier wrote:
> On 2020-10-07 09:05, Marc Zyngier wrote:
>> On 2020-10-06 21:39, Thomas Gleixner wrote:
[...]
>>> This is butt ugly, really. Especially the use case where the tegra
>>> PMC
>>> domain removes itself from the hierarchy from .alloc()
>>
>> I don't disagree at all. It is both horrible and dangerous.
>>
>> My preference would have been to split the PMC domain into discrete
>> domains, each one having having its own depth. But that's incredibly
>> hard to express in DT, and would break the combination of old/new
>> DT and kernel.
>>
>>> That said, I don't have a better idea either. Sigh...
>>
>> A (very minor) improvement would be to turn the trim call in the PMC
>> driver into
>> a flag set in the first invalid irq_data structure, and let
>> __irq_domain_alloc_irqs() do the dirty work.
>>
>> Still crap, but at least would prevent some form of abuse. Thoughts?
>
> Actually, I wonder whether we can have a more general approach:
>
> A partial hierarchy that doesn't have an irq_data->chip pointer
> populated
> cannot be valid. So I wonder if the least ugly thing to do is to just
> drop
> any messing about in the PMC driver, and instead to let
> __irq_domain_alloc_irqs()
> do the culling, always, by looking for a NULL pointer in
> irq_data->chip.
>
> Not any less ugly, but at least doesn't need any driver intervention.
[still talking to myself...]
I implemented that, and it has the advantage of placing the hack in a
single location. It even booted on a garden variety of systems.
I'll post an updated series, and we can compare the various levels
of ugliness.
M.
--
Jazz is not dead. It just smells funny...
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