soc: samsung: exynos-pmu: Add regmap support for SoCs that protect PMU regs

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.

Tested-by: Sam Protsenko <semen.protsenko@linaro.org>
Tested-by: Alexey Klimov <alexey.klimov@linaro.org>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Link: https://lore.kernel.org/r/20240220220613.797068-2-peter.griffin@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

1 files changed, 233 insertions, 2 deletions

diff --git a/drivers/soc/samsung/exynos-pmu.c b/drivers/soc/samsung/exynos-pmu.c
index 250537d7cfd6..fd8b6ac06656 100644
--- a/drivers/soc/samsung/exynos-pmu.c
+++ b/drivers/soc/samsung/exynos-pmu.c
@@ -5,6 +5,7 @@
 //
 // Exynos - CPU PMU(Power Management Unit) support
 
+#include <linux/arm-smccc.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
 #include <linux/mfd/core.h>
@@ -12,19 +13,134 @@
 #include <linux/of_platform.h>
 #include <linux/platform_device.h>
 #include <linux/delay.h>
+#include <linux/regmap.h>
 
 #include <linux/soc/samsung/exynos-regs-pmu.h>
 #include <linux/soc/samsung/exynos-pmu.h>
 
 #include "exynos-pmu.h"
 
+#define PMUALIVE_MASK			GENMASK(13, 0)
+#define TENSOR_SET_BITS			(BIT(15) | BIT(14))
+#define TENSOR_CLR_BITS			BIT(15)
+#define TENSOR_SMC_PMU_SEC_REG		0x82000504
+#define TENSOR_PMUREG_READ		0
+#define TENSOR_PMUREG_WRITE		1
+#define TENSOR_PMUREG_RMW		2
+
 struct exynos_pmu_context {
 	struct device *dev;
 	const struct exynos_pmu_data *pmu_data;
+	struct regmap *pmureg;
 };
 
 void __iomem *pmu_base_addr;
 static struct exynos_pmu_context *pmu_context;
+/* forward declaration */
+static struct platform_driver exynos_pmu_driver;
+
+/*
+ * Tensor SoCs are configured so that PMU_ALIVE registers can only be written
+ * from EL3, but are still read accessible. As Linux needs to write some of
+ * these registers, the following functions are provided and exposed via
+ * regmap.
+ *
+ * Note: This SMC interface is known to be implemented on gs101 and derivative
+ * SoCs.
+ */
+
+/* Write to a protected PMU register. */
+static int tensor_sec_reg_write(void *context, unsigned int reg,
+				unsigned int val)
+{
+	struct arm_smccc_res res;
+	unsigned long pmu_base = (unsigned long)context;
+
+	arm_smccc_smc(TENSOR_SMC_PMU_SEC_REG, pmu_base + reg,
+		      TENSOR_PMUREG_WRITE, val, 0, 0, 0, 0, &res);
+
+	/* returns -EINVAL if access isn't allowed or 0 */
+	if (res.a0)
+		pr_warn("%s(): SMC failed: %d\n", __func__, (int)res.a0);
+
+	return (int)res.a0;
+}
+
+/* Read/Modify/Write a protected PMU register. */
+static int tensor_sec_reg_rmw(void *context, unsigned int reg,
+			      unsigned int mask, unsigned int val)
+{
+	struct arm_smccc_res res;
+	unsigned long pmu_base = (unsigned long)context;
+
+	arm_smccc_smc(TENSOR_SMC_PMU_SEC_REG, pmu_base + reg,
+		      TENSOR_PMUREG_RMW, mask, val, 0, 0, 0, &res);
+
+	/* returns -EINVAL if access isn't allowed or 0 */
+	if (res.a0)
+		pr_warn("%s(): SMC failed: %d\n", __func__, (int)res.a0);
+
+	return (int)res.a0;
+}
+
+/*
+ * Read a protected PMU register. All PMU registers can be read by Linux.
+ * Note: The SMC read register is not used, as only registers that can be
+ * written are readable via SMC.
+ */
+static int tensor_sec_reg_read(void *context, unsigned int reg,
+			       unsigned int *val)
+{
+	*val = pmu_raw_readl(reg);
+	return 0;
+}
+
+/*
+ * For SoCs that have set/clear bit hardware this function can be used when
+ * the PMU register will be accessed by multiple masters.
+ *
+ * For example, to set bits 13:8 in PMU reg offset 0x3e80
+ * tensor_set_bits_atomic(ctx, 0x3e80, 0x3f00, 0x3f00);
+ *
+ * Set bit 8, and clear bits 13:9 PMU reg offset 0x3e80
+ * tensor_set_bits_atomic(0x3e80, 0x100, 0x3f00);
+ */
+static int tensor_set_bits_atomic(void *ctx, unsigned int offset, u32 val,
+				  u32 mask)
+{
+	int ret;
+	unsigned int i;
+
+	for (i = 0; i < 32; i++) {
+		if (!(mask & BIT(i)))
+			continue;
+
+		offset &= ~TENSOR_SET_BITS;
+
+		if (val & BIT(i))
+			offset |= TENSOR_SET_BITS;
+		else
+			offset |= TENSOR_CLR_BITS;
+
+		ret = tensor_sec_reg_write(ctx, offset, i);
+		if (ret)
+			return ret;
+	}
+	return ret;
+}
+
+static int tensor_sec_update_bits(void *ctx, unsigned int reg,
+				  unsigned int mask, unsigned int val)
+{
+	/*
+	 * Use atomic operations for PMU_ALIVE registers (offset 0~0x3FFF)
+	 * as the target registers can be accessed by multiple masters.
+	 */
+	if (reg > PMUALIVE_MASK)
+		return tensor_sec_reg_rmw(ctx, reg, mask, val);
+
+	return tensor_set_bits_atomic(ctx, reg, val, mask);
+}
 
 void pmu_raw_writel(u32 val, u32 offset)
 {
@@ -75,11 +191,41 @@ void exynos_sys_powerdown_conf(enum sys_powerdown mode)
 #define exynos_pmu_data_arm_ptr(data)	NULL
 #endif
 
+static const struct regmap_config regmap_smccfg = {
+	.name = "pmu_regs",
+	.reg_bits = 32,
+	.reg_stride = 4,
+	.val_bits = 32,
+	.fast_io = true,
+	.use_single_read = true,
+	.use_single_write = true,
+	.reg_read = tensor_sec_reg_read,
+	.reg_write = tensor_sec_reg_write,
+	.reg_update_bits = tensor_sec_update_bits,
+};
+
+static const struct regmap_config regmap_mmiocfg = {
+	.name = "pmu_regs",
+	.reg_bits = 32,
+	.reg_stride = 4,
+	.val_bits = 32,
+	.fast_io = true,
+	.use_single_read = true,
+	.use_single_write = true,
+};
+
+static const struct exynos_pmu_data gs101_pmu_data = {
+	.pmu_secure = true
+};
+
 /*
  * PMU platform driver and devicetree bindings.
  */
 static const struct of_device_id exynos_pmu_of_device_ids[] = {
 	{
+		.compatible = "google,gs101-pmu",
+		.data = &gs101_pmu_data,
+	}, {
 		.compatible = "samsung,exynos3250-pmu",
 		.data = exynos_pmu_data_arm_ptr(exynos3250_pmu_data),
 	}, {
@@ -113,19 +259,75 @@ static const struct mfd_cell exynos_pmu_devs[] = {
 	{ .name = "exynos-clkout", },
 };
 
+/**
+ * exynos_get_pmu_regmap() - Obtain pmureg regmap
+ *
+ * Find the pmureg regmap previously configured in probe() and return regmap
+ * pointer.
+ *
+ * Return: A pointer to regmap if found or ERR_PTR error value.
+ */
 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() - Obtain pmureg regmap via phandle
+ * @np: Device node holding PMU phandle property
+ * @propname: Name of property holding phandle value
+ *
+ * Find the pmureg regmap previously configured in probe() and return regmap
+ * pointer.
+ *
+ * Return: A pointer to regmap if found or ERR_PTR error value.
+ */
+struct regmap *exynos_get_pmu_regmap_by_phandle(struct device_node *np,
+						const char *propname)
+{
+	struct exynos_pmu_context *ctx;
+	struct device_node *pmu_np;
+	struct device *dev;
+
+	if (propname)
+		pmu_np = of_parse_phandle(np, propname, 0);
+	else
+		pmu_np = np;
+
+	if (!pmu_np)
+		return ERR_PTR(-ENODEV);
+
+	/*
+	 * Determine if exynos-pmu device has probed and therefore regmap
+	 * has been created and can be returned to the caller. Otherwise we
+	 * return -EPROBE_DEFER.
+	 */
+	dev = driver_find_device_by_of_node(&exynos_pmu_driver.driver,
+					    (void *)pmu_np);
+
+	if (propname)
+		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);
+
 static int exynos_pmu_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
+	struct regmap_config pmu_regmcfg;
+	struct regmap *regmap;
+	struct resource *res;
 	int ret;
 
 	pmu_base_addr = devm_platform_ioremap_resource(pdev, 0);
@@ -137,9 +339,38 @@ static int exynos_pmu_probe(struct platform_device *pdev)
 			GFP_KERNEL);
 	if (!pmu_context)
 		return -ENOMEM;
-	pmu_context->dev = dev;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!res)
+		return -ENODEV;
+
 	pmu_context->pmu_data = of_device_get_match_data(dev);
 
+	/* For SoCs that secure PMU register writes use custom regmap */
+	if (pmu_context->pmu_data && pmu_context->pmu_data->pmu_secure) {
+		pmu_regmcfg = regmap_smccfg;
+		pmu_regmcfg.max_register = resource_size(res) -
+					   pmu_regmcfg.reg_stride;
+		/* Need physical address for SMC call */
+		regmap = devm_regmap_init(dev, NULL,
+					  (void *)(uintptr_t)res->start,
+					  &pmu_regmcfg);
+	} else {
+		/* All other SoCs use a MMIO regmap */
+		pmu_regmcfg = regmap_mmiocfg;
+		pmu_regmcfg.max_register = resource_size(res) -
+					   pmu_regmcfg.reg_stride;
+		regmap = devm_regmap_init_mmio(dev, pmu_base_addr,
+					       &pmu_regmcfg);
+	}
+
+	if (IS_ERR(regmap))
+		return dev_err_probe(&pdev->dev, PTR_ERR(regmap),
+				     "regmap init failed\n");
+
+	pmu_context->pmureg = regmap;
+	pmu_context->dev = dev;
+
 	if (pmu_context->pmu_data && pmu_context->pmu_data->pmu_init)
 		pmu_context->pmu_data->pmu_init();