linux-kernel - Re: [PATCH 0/3] soc: samsung: exynos-pmu: gs101: avoid SError for inaccessible registers

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Message-ID: <CAPLW+4mitF8rDcKdp3Bgs7sF88WbV981hEkM0LiTqYKSLN2_Jw@mail.gmail.com>
Date: Tue, 7 Oct 2025 14:17:54 -0500
From: Sam Protsenko <semen.protsenko@...aro.org>
To: André Draszik <andre.draszik@...aro.org>
Cc: Krzysztof Kozlowski <krzk@...nel.org>, Alim Akhtar <alim.akhtar@...sung.com>, 
	Peter Griffin <peter.griffin@...aro.org>, Tudor Ambarus <tudor.ambarus@...aro.org>, 
	Will McVicker <willmcvicker@...gle.com>, kernel-team@...roid.com, 
	linux-arm-kernel@...ts.infradead.org, linux-samsung-soc@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] soc: samsung: exynos-pmu: gs101: avoid SError for
 inaccessible registers

On Mon, Oct 6, 2025 at 1:36 AM André Draszik <andre.draszik@...aro.org> wrote:
>
> Hi Sam,
>
> On Fri, 2025-10-03 at 11:59 -0500, Sam Protsenko wrote:
> > Hi Andre,
> >
> > On Thu, Oct 2, 2025 at 5:33 AM André Draszik <andre.draszik@...aro.org> wrote:
> > >
> > > Accessing non-existent PMU registers causes an SError, halting the
> > > system and rendering it unuseable.
> > >
> >
> > I wonder if this issue you describe here is similar to what I'm seeing
> > on E850-96. When I'm trying to read these files
> >
> >     /sys/kernel/debug/regmap/dummy-syscon@...000000010020000/registers
> >     /sys/kernel/debug/regmap/dummy-chipid@...000000010000000/registers
> >     /sys/kernel/debug/regmap/dummy-system-controller@...000000011860000/registers
> >
> > I'm seeing "synchronous external abort" during regmap operations
> > (judging from the backtrace). Do you think this series fixes the same
> > issue on gs101?
>
> Yes, but for the system controller (PMU) only.
>
> On E850, it appears to be the same and there are many holes in the PMU memory
> range. You can confirm using debugfs by manually skipping invalid ones, e.g.
>
> dd if=/sys/kernel/debug/regmap/dummy-system-controller@...000000011860000/registers \
>    ibs=15 count=1 \
>    skip=$(( 0x28 / 4 ))
>
> should give you register 0x28 without SError.
>
> while
>
> dd if=/sys/kernel/debug/regmap/dummy-system-controller@...000000011860000/registers \
>    ibs=15 count=1 \
>    skip=$(( 0x4 / 4 ))
>
> should crash.
>

Thanks for the details! Guess I'll wait for your series to be merged first :)

> >  If so, I'd probably want to adapt it for Exynos850
> > later.
>
> +1. Note though that a custom regmap is used on gs101 for the PMU in the first place.
>
>
> Cheers,
> Andre'
>
>
> >