linux-kernel - Re: [PATCH v4 1/2] soc: samsung: exynos-pmu: Add regmap support for SoCs that protect PMU regs

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Message-ID: <CAPLW+4mSyqnkzz5N1seFoaDAR1pd_jQEO3ThkGf3U_ozfwedyA@mail.gmail.com>
Date: Fri, 9 Feb 2024 14:50:48 -0600
From: Sam Protsenko <semen.protsenko@...aro.org>
To: Peter Griffin <peter.griffin@...aro.org>
Cc: arnd@...db.de, krzysztof.kozlowski@...aro.org, linux@...ck-us.net, 
	wim@...ux-watchdog.org, alim.akhtar@...sung.com, jaewon02.kim@...sung.com, 
	alexey.klimov@...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, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH v4 1/2] soc: samsung: exynos-pmu: Add regmap support for
 SoCs that protect PMU regs

On Thu, Feb 8, 2024 at 10:21 AM Peter Griffin <peter.griffin@...aroorg> wrote:
>
> Some Exynos based SoCs like Tensor gs101 protect the PMU registers for
> security hardening reasons so that they are only write 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>
> ---
> Changes since v3:
>  - Fix PMUALIVE_MASK
>  - Add TENSOR_ prefix
>  - clear SET_BITS bits on each loop iteration
>  - change set_bit to set_bits in func name
>  - Fix some alignment
>  - Add missing return on dev_err_probe
>  - Reduce indentation in loop
>
> Changes since v2
>  - Add select REGMAP to Kconfig
>  - Add constant for SET/CLEAR bits
>  - Replace kerneldoc with one line comment
>  - Fix kerneldoc for EXPORT_SYMBOL_GPL funcs
>  - remove superfluous extern keyword
>  - dev_err_probe() on probe error
>  - shorten regmcfg name
>  - no compatibles inside probe, use match data
>  - don't mix declarations with/without initializations
>  - tensor_sec_reg_read() use mmio to avoid access restrictions
>  - Collect up Reviewed-by
>  - const for regmap_config structs
> ---

Tested-by: Sam Protsenko <semen.protsenko@...aro.org>

Tested on my E850-96. All modules that use PMU are still functional
with this patch (watchdog, USB host and Ethernet). No regressions.

[snip]