linux-kernel - Re: [PATCH 2/3] arm64: smp: Implement cpus_has_pending

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Message-ID: <20251006-spiked-beige-gecko-6d8748@sudeepholla>
Date: Mon, 6 Oct 2025 15:41:40 +0100
From: Sudeep Holla <sudeep.holla@....com>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>,
	Sudeep Holla <sudeep.holla@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Maulik Shah <quic_mkshah@...cinc.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] arm64: smp: Implement cpus_has_pending_ipi()

On Mon, Oct 06, 2025 at 02:22:49PM +0200, Ulf Hansson wrote:
> On Mon, 6 Oct 2025 at 12:54, Sudeep Holla <sudeep.holla@....com> wrote:
> >
> > 2. I understand this is intended for the DragonBoard 410c, where the firmware
> >    can’t be updated. However, ideally, the PSCI firmware should handle checking
> >    for pending IPIs if that’s important for the platform. The firmware could
> >    perform this check at the CPU PPU/HW level and prevent entering the
> >    state if needed.
> 
> I think this is exactly what is happening on Dragonboard 410c (see the
> stats I shared in the commit message in patch3).
> 
> The PSCI FW refuses to enter the suggested idlestate and the call fails.
> 

Ah OK, the PSCI FW is doing the job correctly, we are just attempting to
reduce the failures by catching few cases earlier in the OSPM itself ?
Sure it only reduces the failures but it can't eliminate those as IPI might
be issued after this check in the OSPM. I understand the call to firmware
can be prevented.

-- 
Regards,
Sudeep