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Date: Wed, 07 Oct 2020 13:23:58 +0100 From: Marc Zyngier <maz@...nel.org> To: Thomas Gleixner <tglx@...utronix.de> Cc: linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, Thierry Reding <thierry.reding@...il.com>, Jonathan Hunter <jonathanh@...dia.com>, Dmitry Osipenko <digetx@...il.com>, Sowjanya Komatineni <skomatineni@...dia.com>, Venkat Reddy Talla <vreddytalla@...dia.com>, kernel-team@...roid.com Subject: Re: [PATCH v2 1/4] genirq/irqdomain: Allow partial trimming of irq_data hierarchy 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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