linux-kernel - Re: [PATCH v2 1/2] soc: samsung: exynos-pmu: Add regmap support for SoCs that protect PMU regs

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Date: Tue, 30 Jan 2024 15:01:54 +0000
From: Peter Griffin <peter.griffin@...aro.org>
To: Guenter Roeck <linux@...ck-us.net>
Cc: arnd@...db.de, krzysztof.kozlowski@...aro.org, wim@...ux-watchdog.org, 
	alim.akhtar@...sung.com, jaewon02.kim@...sung.com, semen.protsenko@...aro.org, 
	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 v2 1/2] soc: samsung: exynos-pmu: Add regmap support for
 SoCs that protect PMU regs

Hi Guenter,

Thanks for the feedback.

On Tue, 30 Jan 2024 at 06:26, Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 1/29/24 13:19, Peter Griffin wrote:
> > Some Exynos based SoCs like Tensor gs101 protect the PMU registers for
> > security hardening reasons so that they are only accessible in el3 via an
> > SMC call.
> >
> > As most Exynos drivers that need to write PMU registers currently obtain a
> > regmap via syscon (phys, pinctrl, watchdog). Support for the above usecase
> > is implemented in this driver using a custom regmap similar to syscon to
> > handle the SMC call. Platforms that don't secure PMU registers, get a mmio
> > regmap like before. As regmaps abstract out the underlying register access
> > changes to the leaf drivers are minimal.
> >
> > A new API exynos_get_pmu_regmap_by_phandle() is provided for leaf drivers
> > that currently use syscon_regmap_lookup_by_phandle(). This also handles
> > deferred probing.
> >
> > Signed-off-by: Peter Griffin <peter.griffin@...aro.org>
> > ---
> [ ... ]
>
> > +/**
> > + * exynos_get_pmu_regmap
> > + * Find the pmureg previously configured in probe() and return regmap property.
> > + * Return: regmap if found or error if not found.
> > + */
> >   struct regmap *exynos_get_pmu_regmap(void)
> >   {
> >       struct device_node *np = of_find_matching_node(NULL,
> >                                                     exynos_pmu_of_device_ids);
> >       if (np)
> > -             return syscon_node_to_regmap(np);
> > +             return exynos_get_pmu_regmap_by_phandle(np, NULL);
> >       return ERR_PTR(-ENODEV);
> >   }
> >   EXPORT_SYMBOL_GPL(exynos_get_pmu_regmap);
> >
> > +/**
> > + * exynos_get_pmu_regmap_by_phandle
> > + * Find the pmureg previously configured in probe() and return regmap property.
> > + * Return: regmap if found or error if not found.
> > + *
> > + * @np: Pointer to device's Device Tree node
> > + * @property: Device Tree property name which references the pmu
> > + */
> > +struct regmap *exynos_get_pmu_regmap_by_phandle(struct device_node *np,
> > +                                             const char *property)
> > +{
> > +     struct device *dev;
> > +     struct exynos_pmu_context *ctx;
> > +     struct device_node *pmu_np;
> > +
> > +     if (property)
> > +             pmu_np = of_parse_phandle(np, property, 0);
> > +     else
> > +             pmu_np = np;
> > +
> > +     if (!pmu_np)
> > +             return ERR_PTR(-ENODEV);
> > +
> > +     dev = driver_find_device_by_of_node(&exynos_pmu_driver.driver,
> > +                                         (void *)pmu_np);
> > +     of_node_put(pmu_np);
> > +     if (!dev)
> > +             return ERR_PTR(-EPROBE_DEFER);
> > +
> > +     ctx = dev_get_drvdata(dev);
> > +
> > +     return ctx->pmureg;
> > +}
> > +EXPORT_SYMBOL_GPL(exynos_get_pmu_regmap_by_phandle);
> > +
>
> I think there should be a detailed comment explaining why the complexity
> is necessary instead of just returning pmu_context->pmureg.

Ok, I'll add a detailed comment for v3.

Thanks,

Peter