linux-kernel - Re: [PATCH 1/2] irqchip/armada-370-xp: Do not touch Performance Counter Overflow on A375, A38x, A39x

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Message-ID: <20220429223145.4rubhuiu64ktgklp@pali>
Date:   Sat, 30 Apr 2022 00:31:45 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Gregory Clement <gregory.clement@...tlin.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] irqchip/armada-370-xp: Do not touch Performance
 Counter Overflow on A375, A38x, A39x

On Saturday 30 April 2022 00:23:34 Andrew Lunn wrote:
> On Fri, Apr 29, 2022 at 03:05:24PM +0200, Pali Rohár wrote:
> > On Friday 29 April 2022 14:23:08 Andrew Lunn wrote:
> > > On Mon, Apr 25, 2022 at 01:37:05PM +0200, Pali Rohár wrote:
> > > > Register ARMADA_370_XP_INT_FABRIC_MASK_OFFS is Armada 370 and XP specific
> > > > and on new Armada platforms it has different meaning. It does not configure
> > > > Performance Counter Overflow interrupt masking. So do not touch this
> > > > register on non-A370/XP platforms (A375, A38x and A39x).
> > > 
> > > Hi Pali
> > > 
> > > Do the Armada 375, 38x and 39x have an over flow interrupt? I assume
> > > not.
> > 
> > Hello! According to documentation there is something named performance
> > counter interrupt, but it is in different register... and this register
> > is not per-cpu.
> 
> O.K, not something which can be quickly added. 
> 
> > > Does this need a fixes tag? Should it be back ported in stable?
> > 
> > git blame show that this functionality appeared in commit 28da06dfd9e4
> > ("irqchip: armada-370-xp: Enable the PMU interrupts").
> 
> It is more a question of:
> 
>  o It must fix a real bug that bothers people (not a, “This could be a
>    problem…” type thing).
> 
> From https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> 
> Have you seen bad things happen because of this?
> 
>      Andrew

On those new Armada SoCs that register is used for unmasking interrupts
from another hierarchy. Until you start using those new interrupts there
probably could not be any issue. But in any case unmasking unwanted
interrupt is not a wise idea...

I spotted this because I started using those extended interrupts from
another hierarchy. I'm planning to send a patch which properly export
them via DTS. Consumer would be pci-mvebu.c driver as in this extended
hierarchy are PCIe AER and PME interrupts.

Anyway, Fixes tag is probably better in this situation than stable tag.
So would it be fine to replace it by?

Fixes: 28da06dfd9e4 ("irqchip: armada-370-xp: Enable the PMU interrupts")