Re: [PATCH v5 1/2] soc: samsung: exynos-pmu: Add regmap support for SoCs that protect PMU regs

From: Peter Griffin <peter.griffin@linaro.org>
To: Sam Protsenko <semen.protsenko@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,
	 alexey.klimov@linaro.org, kernel-team@android.com,
	tudor.ambarus@linaro.org,  andre.draszik@linaro.org,
	saravanak@google.com, willmcvicker@google.com,
	 linux-fsd@tesla.com, linux-watchdog@vger.kernel.org,
	 linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	 linux-samsung-soc@vger.kernel.org
Subject: Re: [PATCH v5 1/2] soc: samsung: exynos-pmu: Add regmap support for SoCs that protect PMU regs
Date: Tue, 20 Feb 2024 13:20:37 +0000	[thread overview]
Message-ID: <CADrjBPrMC4Zh1yOzfPZ81bfnkz5BG9MktPpgny9r3F0x8mekxw@mail.gmail.com> (raw)
In-Reply-To: <CAPLW+4nOq_62rBhwRUf0RW0zTiGa+-Zpt+FLcTa87biX8Nq-BA@mail.gmail.com>

Hi Sam,

On Mon, 19 Feb 2024 at 23:06, Sam Protsenko <semen.protsenko@linaro.org> wrote:
>
> On Mon, Feb 19, 2024 at 2:42 PM 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 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>
> > ---
> > Changes since v4:
> >  - Use same argument names as in struct regmap_config
> >  - Remove inline keyword and rely on compiler
> >  - Update kerneldoc wording
> >  - property -> propname argument rename
> >  - reverse Xmas tree
> >  - Only call of_node_put() when of_parse_phandle is called
> >  - Collect tags
> >
> > 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
> > ---
> >  drivers/soc/samsung/Kconfig            |   1 +
> >  drivers/soc/samsung/exynos-pmu.c       | 235 ++++++++++++++++++++++++-
> >  drivers/soc/samsung/exynos-pmu.h       |   1 +
> >  include/linux/soc/samsung/exynos-pmu.h |  11 +-
> >  4 files changed, 245 insertions(+), 3 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/exynos-pmu.c
> > index 250537d7cfd6..d6ae8025fdb4 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
> > + * @property: Name of property holding phandle value
>
> This doesn't match the actual param name.

Doh, I missed the kerneldoc comment in the renaming from property ->
propname. I will send a v6 in a moment with this fixed

Peter.