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References: <20240202145731.4082033-1-peter.griffin@linaro.org> <20240202145731.4082033-2-peter.griffin@linaro.org>
In-Reply-To: <20240202145731.4082033-2-peter.griffin@linaro.org>
From: Sam Protsenko <semen.protsenko@linaro.org>
Date: Fri, 2 Feb 2024 11:35:42 -0600
Message-ID: <CAPLW+4=Cm36Q311Y7mCGgm+3fe5NNNc5XhNSMkbigTG2BVCTpA@mail.gmail.com>
Subject: Re: [PATCH v3 1/2] soc: samsung: exynos-pmu: Add regmap support for
 SoCs that protect PMU regs
To: Peter Griffin <peter.griffin@linaro.org>
Cc: arnd@arndb.de, krzysztof.kozlowski@linaro.org, linux@roeck-us.net, 
	wim@linux-watchdog.org, alim.akhtar@samsung.com, jaewon02.kim@samsung.com, 
	kernel-team@android.com, alexey.klimov@linaro.org, tudor.ambarus@linaro.org, 
	andre.draszik@linaro.org, saravanak@google.com, willmcvicker@google.com, 
	linux-fsd@tesla.com, linux-watchdog@vger.kernel.org, 
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org
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On Fri, Feb 2, 2024 at 8:57=E2=80=AFAM Peter Griffin <peter.griffin@linaro.=
org> 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 usecas=
e
> 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 mmi=
o
> regmap like before. As regmaps abstract out the underlying register acces=
s
> 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>
> ---
> 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 superflous 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
> ---
>  drivers/soc/samsung/Kconfig            |   1 +
>  drivers/soc/samsung/exynos-pmu.c       | 233 ++++++++++++++++++++++++-
>  drivers/soc/samsung/exynos-pmu.h       |   1 +
>  include/linux/soc/samsung/exynos-pmu.h |  11 +-
>  4 files changed, 241 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/soc/samsung/Kconfig b/drivers/soc/samsung/Kconfig
> index 27ec99af77e3..1a5dfdc978dc 100644
> --- a/drivers/soc/samsung/Kconfig
> +++ b/drivers/soc/samsung/Kconfig
> @@ -42,6 +42,7 @@ config EXYNOS_PMU
>         depends on ARCH_EXYNOS || ((ARM || ARM64) && COMPILE_TEST)
>         select EXYNOS_PMU_ARM_DRIVERS if ARM && ARCH_EXYNOS
>         select MFD_CORE
> +       select REGMAP_MMIO
>
>  # There is no need to enable these drivers for ARMv8
>  config EXYNOS_PMU_ARM_DRIVERS
> diff --git a/drivers/soc/samsung/exynos-pmu.c b/drivers/soc/samsung/exyno=
s-pmu.c
> index 250537d7cfd6..adf3549370d6 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 +13,130 @@
>  #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(14, 0)

Are you sure it's not GENMASK(13, 0)? Because SET_BITS has bit #14
set, which overlaps with bit #14 from PMUALIVE_MASK, when being added
in tensor_set_bit_atomic().

This also can be aligned with below definitions.

> +#define SET_BITS       0xc000
> +#define CLEAR_BITS     0x8000

All 3 above values seem to be gs101 specific. At least I can't find
any similar atomic registers in Exynos850 TRM, in PMU block. So I'd
suggest also adding TENSOR_ prefix to those to make it clear and to
prevent possible naming conflicts in future.

Also, not sure if it makes things better, but FWIW:

    #define CLEAR_BITS     BIT(15)
    #define SET_BITS       (BIT(15) | BIT(14))

Just to show that those two bits don't overlap with PMUALIVE_MASK (if
it can be fixed to 13:0), and show their relation. If I understand
correctly what's going on anyway.

> +
> +#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;
> +static struct platform_driver exynos_pmu_driver;

Just an idea: maybe add a comment saying it's a forward declaration,
and the variable is assigned below, as it might be confusing. Not sure
if it's worth it though.

> +
> +/*
> + * Tensor SoCs are configured so that PMU_ALIVE registers can only be wr=
itten
> + * 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 deri=
vative
> + * SoCs.
> + */
> +
> +/* Write to a protected PMU register. */
> +static int tensor_sec_reg_write(void *base, unsigned int reg, unsigned i=
nt val)
> +{
> +       struct arm_smccc_res res;
> +       unsigned long pmu_base =3D (unsigned long)base;
> +
> +       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 *base, unsigned int reg,
> +                             unsigned int mask, unsigned int val)
> +{
> +       struct arm_smccc_res res;
> +       unsigned long pmu_base =3D (unsigned long)base;
> +
> +       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 b=
e
> + * written are readable via SMC.
> + */
> +static int tensor_sec_reg_read(void *base, unsigned int reg, unsigned in=
t *val)
> +{
> +       *val =3D pmu_raw_readl(reg);
> +       return 0;
> +}
> +
> +/*
> + * For SoCs that have set/clear bit hardware this function can be used w=
hen
> + * 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 int tensor_set_bit_atomic(void *ctx, unsigned int offset,

set_bit -> set_bits?

> +                                       u32 val, u32 mask)
> +{
> +       int ret;
> +       unsigned int i;
> +
> +       for (i =3D 0; i < 32; i++) {
> +               if (mask & BIT(i)) {

Maybe replace it with:

    if (!(mask & BIT(i)))
        continue;

to reduce the indentation level?

> +                       if (val & BIT(i))
> +                               offset |=3D SET_BITS;
> +                       else
> +                               offset |=3D CLEAR_BITS;

What if someone calls this functions like this:

    tensor_set_bit_atomic(0x3e80, 0x100, 0x3f00);

which means "set bit #8, and clear bits 13:9). But because the offset
variable will hold SET_BITS set during bit #8 handling, bits 13:9 are
also going to be set, effectively making that call act like
tensor_set_bit_atomic(0x3e80, 0x3f00, 0x3f00) instead. So I'd add
something like:

    offset &=3D ~SET_BITS;

before doing |=3D operations.

> +
> +                       ret =3D tensor_sec_reg_write(ctx, offset, i);
> +                       if (ret)
> +                               goto out;

Maybe remove "out" and just do return ret here?

> +               }
> +       }
> +out:
> +       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_bit_atomic(ctx, reg, val, mask);
> +}
>
>  void pmu_raw_writel(u32 val, u32 offset)
>  {
> @@ -75,11 +187,41 @@ void exynos_sys_powerdown_conf(enum sys_powerdown mo=
de)
>  #define exynos_pmu_data_arm_ptr(data)  NULL
>  #endif
>
> +static const struct regmap_config regmap_smccfg =3D {
> +       .name =3D "pmu_regs",
> +       .reg_bits =3D 32,
> +       .reg_stride =3D 4,
> +       .val_bits =3D 32,
> +       .fast_io =3D true,
> +       .use_single_read =3D true,
> +       .use_single_write =3D true,
> +       .reg_read =3D tensor_sec_reg_read,
> +       .reg_write =3D tensor_sec_reg_write,
> +       .reg_update_bits =3D tensor_sec_update_bits,
> +};
> +
> +static const struct regmap_config regmap_mmiocfg =3D {
> +       .name =3D "pmu_regs",
> +       .reg_bits =3D 32,
> +       .reg_stride =3D 4,
> +       .val_bits =3D 32,
> +       .fast_io =3D true,
> +       .use_single_read =3D true,
> +       .use_single_write =3D true,
> +};
> +
> +static const struct exynos_pmu_data gs101_pmu_data =3D {
> +       .pmu_secure =3D true
> +};
> +
>  /*
>   * PMU platform driver and devicetree bindings.
>   */
>  static const struct of_device_id exynos_pmu_of_device_ids[] =3D {
>         {
> +               .compatible =3D "google,gs101-pmu",
> +               .data =3D &gs101_pmu_data,
> +       }, {
>                 .compatible =3D "samsung,exynos3250-pmu",
>                 .data =3D exynos_pmu_data_arm_ptr(exynos3250_pmu_data),
>         }, {
> @@ -113,19 +255,73 @@ static const struct mfd_cell exynos_pmu_devs[] =3D =
{
>         { .name =3D "exynos-clkout", },
>  };
>
> +/**
> + * exynos_get_pmu_regmap() - Obtain pmureg regmap
> + *
> + * Find the pmureg regmap previously configured in probe() and return re=
gmap
> + * pointer.
> + *
> + * Return: A pointer to regmap if found or ERR_PTR error value.
> + */
>  struct regmap *exynos_get_pmu_regmap(void)
>  {
>         struct device_node *np =3D of_find_matching_node(NULL,
>                                                       exynos_pmu_of_devic=
e_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: Pointer to device's Device Tree node
> + * @property: Device Tree property name which references the pmu
> + *
> + * Find the pmureg regmap previously configured in probe() and return re=
gmap
> + * 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 *property)
> +{
> +       struct device *dev;
> +       struct exynos_pmu_context *ctx;
> +       struct device_node *pmu_np;
> +
> +       if (property)
> +               pmu_np =3D of_parse_phandle(np, property, 0);
> +       else
> +               pmu_np =3D 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 =3D 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 =3D 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 =3D &pdev->dev;
> +       struct regmap_config pmu_regmcfg;
> +       struct regmap *regmap;
> +       struct resource *res;
>         int ret;
>
>         pmu_base_addr =3D devm_platform_ioremap_resource(pdev, 0);
> @@ -133,13 +329,42 @@ static int exynos_pmu_probe(struct platform_device =
*pdev)
>                 return PTR_ERR(pmu_base_addr);
>
>         pmu_context =3D devm_kzalloc(&pdev->dev,
> -                       sizeof(struct exynos_pmu_context),
> -                       GFP_KERNEL);
> +                                  sizeof(struct exynos_pmu_context),
> +                                  GFP_KERNEL);
>         if (!pmu_context)
>                 return -ENOMEM;
> -       pmu_context->dev =3D dev;
> +
> +       res =3D platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +       if (!res)
> +               return -ENODEV;
> +
>         pmu_context->pmu_data =3D 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 =3D regmap_smccfg;
> +               pmu_regmcfg.max_register =3D resource_size(res) -
> +                                          pmu_regmcfg.reg_stride;
> +               /* Need physical address for SMC call */
> +               regmap =3D devm_regmap_init(dev, NULL,
> +                                         (void *)(uintptr_t)res->start,
> +                                         &pmu_regmcfg);
> +       } else {
> +               /* all other SoCs use a MMIO regmap */

Suggest starting with a capital letter, for consistency with previous comme=
nts.

> +               pmu_regmcfg =3D regmap_mmiocfg;
> +               pmu_regmcfg.max_register =3D resource_size(res) -
> +                                          pmu_regmcfg.reg_stride;
> +               regmap =3D devm_regmap_init_mmio(dev, pmu_base_addr,
> +                                              &pmu_regmcfg);
> +       }
> +
> +       if (IS_ERR(regmap))
> +               dev_err_probe(&pdev->dev, PTR_ERR(regmap),
> +                             "regmap init failed\n");

Why not "return dev_err_probe()"? Is it ok to continue with no regmap creat=
ed?

> +
> +       pmu_context->pmureg =3D regmap;
> +       pmu_context->dev =3D dev;
> +
>         if (pmu_context->pmu_data && pmu_context->pmu_data->pmu_init)
>                 pmu_context->pmu_data->pmu_init();
>
> diff --git a/drivers/soc/samsung/exynos-pmu.h b/drivers/soc/samsung/exyno=
s-pmu.h
> index 1c652ffd79b4..0a49a2c9a08e 100644
> --- a/drivers/soc/samsung/exynos-pmu.h
> +++ b/drivers/soc/samsung/exynos-pmu.h
> @@ -21,6 +21,7 @@ struct exynos_pmu_conf {
>  struct exynos_pmu_data {
>         const struct exynos_pmu_conf *pmu_config;
>         const struct exynos_pmu_conf *pmu_config_extra;
> +       bool pmu_secure;
>
>         void (*pmu_init)(void);
>         void (*powerdown_conf)(enum sys_powerdown);
> diff --git a/include/linux/soc/samsung/exynos-pmu.h b/include/linux/soc/s=
amsung/exynos-pmu.h
> index a4f5516cc956..406ed73614fd 100644
> --- a/include/linux/soc/samsung/exynos-pmu.h
> +++ b/include/linux/soc/samsung/exynos-pmu.h
> @@ -20,12 +20,21 @@ 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);
> +struct regmap *exynos_get_pmu_regmap(void);
> +

Usually empty line delimeter is not needed in cases like that.

> +struct regmap *exynos_get_pmu_regmap_by_phandle(struct device_node *np,
> +                                               const char *property);
>  #else
>  static inline struct regmap *exynos_get_pmu_regmap(void)
>  {
>         return ERR_PTR(-ENODEV);
>  }
> +
> +static inline struct regmap *exynos_get_pmu_regmap_by_phandle(struct dev=
ice_node *np,
> +                                                             const char =
*property)
> +{
> +       return ERR_PTR(-ENODEV);
> +}
>  #endif
>
>  #endif /* __LINUX_SOC_EXYNOS_PMU_H */
> --
> 2.43.0.594.gd9cf4e227d-goog
>