[PATCH] irqchip: riscv-imsic: Add kernel parameter to disable IPIs

[Anup Patel]

On Tue, Jul 1, 2025 at 1:04 PM Thomas Gleixner <tglx at linutronix.de> wrote:
>
> On Tue, Jul 01 2025 at 12:00, Anup Patel wrote:
> > On Mon, Jun 30, 2025 at 9:39 PM Thomas Gleixner <tglx at linutronix.de> wrote:
> >> > When injecting IPIs to a set of harts, the IMSIC IPI support will
> >> > do a separate MMIO write to SETIPNUM_LE register of each target
> >> > hart. This means on a platform where IMSIC is trap-n-emulated,
> >> > there will be N MMIO traps when injecting IPI to N target harts
> >> > hence IPIs based on IMSIC software injected MSI is slow compared
> >> > to the SBI IPI extension.
> >> >
> >> > Add a kernel parameter to disable IPIs in IMSIC driver for platforms
> >> > with trap-n-emulated IMSIC.
> >>
> >> Why do you need a kernel parameter for that. If the platform uses trap-n
> >> emulation, then disable the IPI muck automatically, no?
> >>
> > Unfortunately, we don't have DT, ACPI, or any other way of discovering
> > whether underlying IMSIC is trap-n-emulated. In fact, the DT or ACPI
> > passed to a KVM Guest is the same irrespective of whether underlying
> > IMSIC is trap-n-emulated or backed by hardware IMSIC VS-file.
>
> Sigh.
>
> > Using software injected MSIs as IPIs is purely a software choice in the
> > IMSIC driver so this new kernel parameter allows users to override it.
>
> Please add that information to the change log.
>

Okay, I will add these details to the patch description.

Regards,
Anup