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

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@linaro.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.

Thanks,
Guenter


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