Re: [PATCH] RISC-V: Allow drivers to provide custom read_cycles64 for M-mode kernel

[Anup Patel]

On Mon, Sep 7, 2020 at 11:48 AM Christoph Hellwig <hch@xxxxxx> wrote:
>
> On Sat, Sep 05, 2020 at 11:05:48AM +0530, Anup Patel wrote:
> > Your patch will also break if the SOC specific timer has a 32bit
> > free-running counter
> > unlike the 64bit free-running counter found on CLINT.
> >
> > I guess it's better to let the SOC timer driver provide the
> > method/function to read the
> > free-running counter.
>
> Seriously, build the interfaces once you know the consumers.  Don't
> build pie in the sky interfaces just because you can, because that
> is what creates all the problems.
>
> And of coruse at least for IPIs which absolutely are performance
> criticical we need a standard interface (one that doesn't suck as much
> as the SBI detour with the four extra context switches).  But I guess
> I have already given up on RISC-V because the incompetency about things
> like the irq design are just so horrible that it isn't worth bothering
> any more.

Most of us are aware of these issues. The SBI IPI call will eventually
become fallback option once we have standard mechanism for IPI in
RISC-V privilege spec. Until then we try our best to support all existing
RISC-V systems out there. This also means we end-up supporting
existing SOC specific timers and IPI injection mechanisms.

Regards,
Anup