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

[Krzysztof Kozlowski]

On 29/01/2024 22:19, 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@xxxxxxxxxx>
> ---
>  drivers/soc/samsung/exynos-pmu.c       | 227 ++++++++++++++++++++++++-
>  include/linux/soc/samsung/exynos-pmu.h |  10 ++
>  2 files changed, 236 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/soc/samsung/exynos-pmu.c b/drivers/soc/samsung/exynos-pmu.c
> index 250537d7cfd6..7bcc144e53a2 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>
> @@ -12,20 +13,159 @@
>  #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"
>  
> +static struct platform_driver exynos_pmu_driver;

I don't understand why do you need it. You can have only one
pmu_context. The moment you probe second one, previous becomes invalid.

I guess you want to parse phandle and check if just in case if it points
to the right device, but still the original code is not ready for two
PMU devices. I say either this problem should be solved entirely,
allowing two devices, or just compare device node from phandle with
device node of exynos_pmu_context->dev and return -EINVAL on mismatches.

Anyway, keep all file scope declarations together.


> +
> +#define PMUALIVE_MASK GENMASK(14, 0)
> +
>  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;
>  
> +/*
> + * Tensor SoCs are configured so that PMU_ALIVE registers can only be written
> + * from el3. As Linux needs to write some of these registers, the following
> + * SMC register read/write/read,write,modify interface is used.
> + *
> + * Note: This SMC interface is known to be implemented on gs101 and derivative
> + * SoCs.
> + */
> +#define TENSOR_SMC_PMU_SEC_REG			(0x82000504)
> +#define TENSOR_PMUREG_READ			0
> +#define TENSOR_PMUREG_WRITE			1
> +#define TENSOR_PMUREG_RMW			2
> +
> +/**
> + * tensor_sec_reg_write
> + * Write to a protected SMC register.
> + * @base: Base address of PMU
> + * @reg:  Address offset of register
> + * @val:  Value to write
> + * Return: (0) on success
> + *

This does not really look like kerneldoc...

> + */
> +static int tensor_sec_reg_write(void *base, unsigned int reg, unsigned int val)
> +{
> +	struct arm_smccc_res res;
> +	unsigned long pmu_base = (unsigned long)base;
> +
> +	arm_smccc_smc(TENSOR_SMC_PMU_SEC_REG,
> +		      pmu_base + reg,
> +		      TENSOR_PMUREG_WRITE,
> +		      val, 0, 0, 0, 0, &res);
> +
> +	if (res.a0)
> +		pr_warn("%s(): SMC failed: %lu\n", __func__, res.a0);
> +
> +	return (int)res.a0;
> +}
> +
> +/**
> + * tensor_sec_reg_rmw
> + * Read/Modify/Write to a protected SMC register.
> + * @base: Base address of PMU
> + * @reg:  Address offset of register
> + * @val:  Value to write
> + * Return: (0) on success
> + *
> + */
> +static int tensor_sec_reg_rmw(void *base, unsigned int reg,
> +			      unsigned int mask, unsigned int val)
> +{
> +	struct arm_smccc_res res;
> +	unsigned long pmu_base = (unsigned long)base;
> +
> +	arm_smccc_smc(TENSOR_SMC_PMU_SEC_REG,
> +		      pmu_base + reg,
> +		      TENSOR_PMUREG_RMW,
> +		      mask, val, 0, 0, 0, &res);
> +
> +	if (res.a0)
> +		pr_warn("%s(): SMC failed: %lu\n", __func__, res.a0);
> +
> +	return (int)res.a0;
> +}
> +
> +/**
> + * tensor_sec_reg_read
> + * Read a protected SMC register.
> + * @base: Base address of PMU
> + * @reg:  Address offset of register
> + * @val:  Value read
> + * Return: (0) on success
> + */
> +static int tensor_sec_reg_read(void *base, unsigned int reg, unsigned int *val)
> +{
> +	struct arm_smccc_res res;
> +	unsigned long pmu_base = (unsigned long)base;
> +
> +	arm_smccc_smc(TENSOR_SMC_PMU_SEC_REG,
> +		      pmu_base + reg,
> +		      TENSOR_PMUREG_READ,
> +		      0, 0, 0, 0, 0, &res);
> +
> +	*val = (unsigned int)res.a0;
> +
> +	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_bit_atomic(0x3e80, 0x3f00, 0x3f00);
> + *
> + * To clear bits 13:8 in PMU offset 0x3e80
> + * tensor_set_bit_atomic(0x3e80, 0x0, 0x3f00);
> + */
> +static inline void tensor_set_bit_atomic(void *ctx, unsigned int offset,
> +					 u32 val, u32 mask)
> +{
> +	unsigned int i;
> +
> +	for (i = 0; i < 32; i++) {
> +		if (mask & BIT(i)) {
> +			if (val & BIT(i)) {
> +				offset |= 0xc000;
> +				tensor_sec_reg_write(ctx, offset, i);
> +			} else {
> +				offset |= 0x8000;
> +				tensor_sec_reg_write(ctx, offset, i);
> +			}
> +		}
> +	}
> +}
> +
> +int tensor_sec_update_bits(void *ctx, unsigned int reg, unsigned int mask, unsigned int val)
> +{
> +	int ret = 0;
> +
> +	/*
> +	 * 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);
> +
> +	tensor_set_bit_atomic(ctx, reg, val, mask);
> +
> +	return ret;
> +}
> +
>  void pmu_raw_writel(u32 val, u32 offset)
>  {
>  	writel_relaxed(val, pmu_base_addr + offset);
> @@ -80,6 +220,8 @@ void exynos_sys_powerdown_conf(enum sys_powerdown mode)
>   */
>  static const struct of_device_id exynos_pmu_of_device_ids[] = {
>  	{
> +		.compatible = "google,gs101-pmu",
> +	}, {
>  		.compatible = "samsung,exynos3250-pmu",
>  		.data = exynos_pmu_data_arm_ptr(exynos3250_pmu_data),
>  	}, {
> @@ -113,19 +255,73 @@ static const struct mfd_cell exynos_pmu_devs[] = {
>  	{ .name = "exynos-clkout", },
>  };
>  
> +/**
> + * 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.

Return is the last. This does not look tested - make htmldocs, make W=1

> + *
> + * @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);
> +
> +static struct regmap_config pmu_regs_regmap_cfg = {
> +	.name = "pmu_regs",
> +	.reg_bits = 32,
> +	.reg_stride = 4,
> +	.val_bits = 32,
> +	.fast_io = true,
> +	.use_single_read = true,
> +	.use_single_write = true,
> +};
> +
>  static int exynos_pmu_probe(struct platform_device *pdev)
>  {
> +	struct resource *res;
> +	struct regmap *regmap;
> +	struct regmap_config pmuregmap_config = pmu_regs_regmap_cfg;
>  	struct device *dev = &pdev->dev;
> +	struct device_node *np = dev->of_node;

Please do not mix order declarations with and without initializations. I
propose first ones with initializations, followed by ones without.

>  	int ret;
>  
>  	pmu_base_addr = devm_platform_ioremap_resource(pdev, 0);
> @@ -137,6 +333,35 @@ static int exynos_pmu_probe(struct platform_device *pdev)
>  			GFP_KERNEL);
>  	if (!pmu_context)
>  		return -ENOMEM;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	if (!res)
> +		return -ENODEV;
> +
> +	pmuregmap_config.max_register = resource_size(res) -
> +				     pmuregmap_config.reg_stride;
> +
> +	if (of_device_is_compatible(np, "google,gs101-pmu")) {

No compatibles inside the probe. Use driver match data. This applies to
all drivers in all subsystems.

> +		pmuregmap_config.reg_read = tensor_sec_reg_read;
> +		pmuregmap_config.reg_write = tensor_sec_reg_write;
> +		pmuregmap_config.reg_update_bits = tensor_sec_update_bits;

No, regmap_config should be const and please use match data.

> +
> +		/* Need physical address for SMC call */
> +		regmap = devm_regmap_init(dev, NULL,
> +					  (void *)(uintptr_t)res->start,
> +					  &pmuregmap_config);
> +	} else {
> +		pmuregmap_config.max_register = resource_size(res) - 4;
> +		regmap = devm_regmap_init_mmio(dev, pmu_base_addr,
> +					       &pmuregmap_config);
> +	}
> +
> +	if (IS_ERR(regmap)) {
> +		pr_err("regmap init failed\n");

dev_err

> +		return PTR_ERR(regmap);
> +	}
> +
> +	pmu_context->pmureg = regmap;
>  	pmu_context->dev = dev;
>  	pmu_context->pmu_data = of_device_get_match_data(dev);
>  
> diff --git a/include/linux/soc/samsung/exynos-pmu.h b/include/linux/soc/samsung/exynos-pmu.h
> index a4f5516cc956..68fb01ba6bef 100644
> --- a/include/linux/soc/samsung/exynos-pmu.h
> +++ b/include/linux/soc/samsung/exynos-pmu.h
> @@ -21,11 +21,21 @@ enum sys_powerdown {
>  extern void exynos_sys_powerdown_conf(enum sys_powerdown mode);
>  #ifdef CONFIG_EXYNOS_PMU
>  extern struct regmap *exynos_get_pmu_regmap(void);
> +
> +extern struct regmap *exynos_get_pmu_regmap_by_phandle(struct device_node *np,
> +						       const char *property);

Drop extern from new code. I understand it makes it inconsistent but it
extern does not matter, so at some point we will clean all existing code...

Best regards,
Krzysztof