Messages in this thread | | | From | Anup Patel <> | Date | Wed, 5 Sep 2018 10:06:24 +0530 | Subject | Re: [RFC PATCH 1/5] RISC-V: Make IPI triggering flexible |
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On Wed, Sep 5, 2018 at 12:20 AM, Christoph Hellwig <hch@infradead.org> wrote: > On Tue, Sep 04, 2018 at 06:15:10PM +0530, Anup Patel wrote: >> The mechanism to trigger IPI is generally part of interrupt-controller >> driver for various architectures. On RISC-V, we have an option to trigger >> IPI using SBI or SOC vendor can implement RISC-V CPU where IPI will be >> triggered using SOC interrupt-controller (e.g. custom PLIC). > > Which is exactly what we want to avoid, and should not make it easy. > > The last thing we need is non-standard whacky IPI mechanisms, and > that is why we habe SBI calls for it. I think we should simply > stat that if an RISC-V cpu design bypasse the SBI for no good reason > we'll simply not support it.
It's outrageous to call IPI mechanisms using interrupt-controller as "wacky".
Lot of architectures have well thought-out interrupt-controller designs with IPI support.
In fact having IPIs through interrupt-controller drivers is much faster because SBI call will have it's own overhead and M-mode code with eventually write to some platform-specific/interrupt-controller register. The SBI call only makes sense for very simple interrupt-controller (such as PLIC) which do not provide IPI mechanism. It totally seems like SBI call for triggering IPIs was added as workaround to address limitations of current PLIC.
RISC-V systems require a more mature and feature complete interrupt-controllers which supports IPIs, PCI MSI, and Virtualization Extensions.
I am sure will see a much better interrupt controller (PLIC++ or something else) soon.
> > So NAK for this patch.
I think you jumped the gun to quickly here.
This patch does two things: 1. Adds a pluggable IPI triggering mechanism 2. Make IPI handling mechanism more generic so that we can call IPI handler from interrupt-controller driver.
Your primary objection seems to be for point1 above. I will drop that part only keep changes related to point2 above.
Regards, Anup
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