Re: [PATCH v2 3/5] irqchip: RISC-V Local Interrupt Controller Driver

[Palmer Dabbelt]

On Tue, 25 Sep 2018 22:54:48 PDT (-0700), anup@xxxxxxxxxxxxxx wrote:
> On Mon, Sep 17, 2018 at 7:58 PM Anup Patel <anup@xxxxxxxxxxxxxx> wrote:
> > On Mon, Sep 17, 2018 at 7:44 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> > >
> > > On Mon, Sep 10, 2018 at 10:08:58PM +0530, Anup Patel wrote:
> > > > > They could in theory IFF someone actually get the use case through
> > > > > the riscv privileged spec working group.
> > > >
> > > > Their is no point in having each and every possible local interrupts
> > > > defined by RISC-V spec because some of these will be CPU
> > > > implementation specific in which case these local interrupts will
> > > > be described in platform specific DT passed to Linux.
> > >
> > > Again, to legally have implementation specific local interrupt types
> > > you'll first need to convice the spec to change the status for those
> > > fields from reserved to implementation specific.
> >
> > I agree, this needs to be first clarified in RISC-V spec. May be this is
> > a good topic for discussion in any upcoming RISC-V meetup.
> >
> > Until then anyone can try these patches from riscv_intc_v2 branch of
> > https://github.com/avpatel/linux
>
> I released that CLIC is going to be available for both M-mode and S-mode.
> Software can choose to use HLIC or CLIC based on it's own preference.
>
> If we are going to support both HLIC and CLIC in Linux kernel for per-CPU
> local interrupts then we should definitely have irqdomain and irqchip for
> per-CPU local interrupts. The selection between HLIC and CLIC will be
> based on which driver gets probed via DT.

Yes, and note that the CLIC is actually an extension of what is currently 
available.  Thus we could produce a single driver that supports both, with 
features selected based on a DT entry.

I'm not sure if a native CLIC driver buys us anything in Linux, though, as 
IIRC there aren't that many CLIC features that will be particularly useful in 
our space.