linux-kernel - Re: [PATCH 1/2] perf: dsu: Allow multiple devices share same IRQ.

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Message-ID: <20200319143510.GB4876@lakrids.cambridge.arm.com>
Date:   Thu, 19 Mar 2020 14:35:11 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Tuan Phan <tuanphan@...amperecomputing.com>
Cc:     patches@...erecomputing.com, Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] perf: dsu: Allow multiple devices share same IRQ.

On Thu, Mar 19, 2020 at 02:32:51PM +0000, Mark Rutland wrote:
> On Tue, Mar 17, 2020 at 05:26:15PM -0700, Tuan Phan wrote:
> > Add IRQF_SHARED flag when register IRQ such that multiple dsu
> > devices can share same IRQ.
> > 
> > Signed-off-by: Tuan Phan <tuanphan@...amperecomputing.com>
> 
> I don't think that this makes sense; further I think that this
> highlights that the current driver doesn't support such a configuration
> for other reasons.
> 
> A DSU instance can only be accessed from a CPU associated with it, since
> it's accessed via sysregs. The IRQ handler must run on one of those
> CPUs.
> 
> To handle that, the DSU PMU driver will need to gain an understanding of
> which CPUs are associated with the instance. As it stands the driver
> seems to assume that there's a single DSU instance, and that all CPUs
> are affine to that same instance.

Sorry, I misread dsu_pmu_get_online_cpu_any_but(), multiple instances
are handled already.

> So NAK to this patch, given the above.

Regardless, this NAK stands.

Thanks,
Mark.