linux-kernel - Re: [PATCH 2/9] soc: samsung: exynos-pmu: Add exynos_pmu

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Date: Wed, 24 Jan 2024 10:02:27 +0000
From: Peter Griffin <peter.griffin@...aro.org>
To: Sam Protsenko <semen.protsenko@...aro.org>
Cc: arnd@...db.de, robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org, 
	linux@...ck-us.net, wim@...ux-watchdog.org, conor+dt@...nel.org, 
	alim.akhtar@...sung.com, jaewon02.kim@...sung.com, chanho61.park@...sung.com, 
	kernel-team@...roid.com, tudor.ambarus@...aro.org, andre.draszik@...aro.org, 
	saravanak@...gle.com, willmcvicker@...gle.com, linux-fsd@...la.com, 
	linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH 2/9] soc: samsung: exynos-pmu: Add exynos_pmu_update/read/write
 APIs and SoC quirks

Hi Sam,

Thanks for the review feedback.

On Tue, 23 Jan 2024 at 18:56, Sam Protsenko <semen.protsenko@...aro.org> wrote:
>
> On Mon, Jan 22, 2024 at 4:57 PM Peter Griffin <peter.griffin@...aro.org> wrote:
> >
> > Newer Exynos SoCs have atomic set/clear bit hardware for PMU registers as
> > these registers can be accessed by multiple masters. Some platforms also
> > protect the PMU registers for security hardening reasons so they can't be
> > written by normal world and are only write acessible in el3 via a SMC call.
> >
> > Add support for both of these usecases using SoC specific quirks that are
> > determined from the DT compatible string.
> >
> > Drivers which need to read and write PMU registers should now use these
> > new exynos_pmu_*() APIs instead of obtaining a regmap using
> > syscon_regmap_lookup_by_phandle()
> >
> > Depending on the SoC specific quirks, the exynos_pmu_*() APIs will access
> > the PMU register in the appropriate way.
> >
> > Signed-off-by: Peter Griffin <peter.griffin@...aro.org>
> > ---
> >  drivers/soc/samsung/exynos-pmu.c       | 209 ++++++++++++++++++++++++-
> >  drivers/soc/samsung/exynos-pmu.h       |   4 +
> >  include/linux/soc/samsung/exynos-pmu.h |  28 ++++
> >  3 files changed, 234 insertions(+), 7 deletions(-)
> >
>
> [snip]
>
> > +
> > +int exynos_pmu_update_bits(unsigned int offset, unsigned int mask,
> > +                          unsigned int val)
> > +{
> > +       if (pmu_context->pmu_data &&
> > +           pmu_context->pmu_data->quirks & QUIRK_PMU_ALIVE_WRITE_SEC)
> > +               return rmw_priv_reg(pmu_context->pmu_base_pa + offset,
> > +                                   mask, val);
> > +
> > +       return regmap_update_bits(pmu_context->pmureg, offset, mask, val);
> > +}
> > +EXPORT_SYMBOL(exynos_pmu_update_bits);
> > +
>
> This seems a bit hacky, from the design perspective. This way the user
> will have to worry about things like driver dependencies, making sure
> everything is instantiated in a correct order, etc. It also hides the
> details otherwise visible through "syscon-phandle" property in the
> device tree.

In v2 I will keep the phandle to pmu_system_controller in DT, and add
some -EPROBE_DEFER logic (See my email with Krzysztof).

> Can we instead rework it by overriding regmap
> implementation for Exynos specifics, and then continue to use it in
> the leaf drivers via "syscon-phandle" property?

I did look at that possibility first, as like you say it would avoid
updating the leaf drivers to use the new API. Unfortunately a SMC
backend to regmap was already tried and nacked upstream pretty hard.
See here https://lore.kernel.org/lkml/20210723163759.GI5221@sirena.org.uk/T/

regards,

Peter.