Re: [PATCH 01/10] irqchip: irq-mips-gic: export gic_send_ipi

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 08/24/2015 04:07 PM, Thomas Gleixner wrote:
On Mon, 24 Aug 2015, Qais Yousef wrote:
On 08/24/2015 02:32 PM, Marc Zyngier wrote:
I'd rather see something more "architected" than this blind export, or
at least some level of filtering (the idea random drivers can access
such a low-level function doesn't make me feel very good).
I don't know how to architect this better or how to perform  the filtering,
but I'm happy to hear suggestions and try them out.
Keep in mind that detecting GIC and writing your own gic_send_ipi() is very
simple. I have done this when the driver was out of tree. So restricting it by
not exporting it will not prevent someone from really accessing the
functionality, it's just they have to do it their own way.
Keep in mind that we are not talking about out of tree hackery. We
talk about a kernel code submission and I doubt, that you will get
away with a GIC detection/fiddling burried in your driver code.

Keep in mind that just slapping an export to some random function is
not much better than doing a GIC hack in the driver.

Marcs concerns about blindly exposing IPI functionality to drivers is
well justified and that kind of coprocessor stuff is not unique to
your particular SoC. We're going to see such things more frequently in
the not so distant future, so we better think now about proper
solutions to that problem.

Sure I'm not trying to argue against that.


There are a couple of issues to solve:

1) How is the IPI which is received by the coprocessor reserved in the
    system?

2) How is it associated to a particular driver?

Shouldn't 'interrupts' property in DT take care of these 2 questions? Maybe we can give it an alias name to make it more readable that this interrupt is requested for external IPI.


3) How do we ensure that a driver cannot issue random IPIs and can
    only send the associated ones?

If we get the irq number from DT then I'm not sure how feasible it is to implement a generic_send_ipi() function that takes this number to generate an IPI.

Do you think this approach would work?


None of these issues are handled by your export.

So we need a core infrastructure which allows us to do that. The
requirements are pretty clear from the above and Marc might have some
further restrictions in mind.

Another issue I'm having which is related is that I need to communicate these GIC irq numbers to AXD core when it starts up. So the logic is that these IPIs are not hardwired and it's up to the system designer to allocate 2 free GIC irqs to be used for that purpose. At the moment I have my own DT property to take these numbers. Hopefully this link would explain the issue. See the question about gic-irq property.

    https://lkml.org/lkml/2015/8/24/459

From what I know there's no generic way for the driver to get the hw irq number from linux irq number unless I missed something. Is it possible to add something to support this? Or maybe there's something but I failed to find?

Thanks,
Qais


Thanks,

	tglx





[Index of Archives]     [Linux MIPS Home]     [LKML Archive]     [Linux ARM Kernel]     [Linux ARM]     [Linux]     [Git]     [Yosemite News]     [Linux SCSI]     [Linux Hams]

  Powered by Linux