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

[Peter Griffin]

Hi Sam,

Thanks for the review feedback.

On Mon, 29 Jan 2024 at 23:01, Sam Protsenko <semen.protsenko@xxxxxxxxxx> wrote:
>
> On Mon, Jan 29, 2024 at 3:19 PM Peter Griffin <peter.griffin@xxxxxxxxxx> 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;
> > +
> > +#define PMUALIVE_MASK GENMASK(14, 0)
>
> I'd advice to keep all #define's right after #include's block.

OK will move
>
> > +
> >  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
>
> Suggest changing el3 to EL3.

Will fix
>
> > + * SMC register read/write/read,write,modify interface is used.
>
> Frankly, I don't really get what does this line mean.

It was just trying to describe the 3 defines below (PMUREG_READ,
PMUREG_WRITE, PMUREG_RMW but if it is unclear then I will remove it.
The idea of the comment was to make things clearer, not add confusion
;-)
>
> > + *
> > + * Note: This SMC interface is known to be implemented on gs101 and derivative
> > + * SoCs.
> > + */
> > +#define TENSOR_SMC_PMU_SEC_REG                 (0x82000504)
>
> Braces are probably not needed here.

Will remove

>
> > +#define TENSOR_PMUREG_READ                     0
> > +#define TENSOR_PMUREG_WRITE                    1
> > +#define TENSOR_PMUREG_RMW                      2
>
> I'd advice to keep all #define's right after #include's block.

Will move

>
> > +
> > +/**
> > + * tensor_sec_reg_write
>
> That doesn't look like a commonly used kernel-doc style. Please check
> [1] and re-format accordingly. I'd also add that this function's
> signature is quite self-explanatory, and it's also static, so I'm not
> sure if it deserves kernel-doc comment or if it just makes things more
> cluttered in this case. Maybe one-line regular comment will do here?

Ok will update to one line comment


> If you still thinks kernel-doc works better, please also check it with
>
>     $ scripts/kernel-doc -v -none drivers/soc/samsung/exynos-pmu.c
>     $ scripts/kernel-doc -v drivers/soc/samsung/exynos-pmu.c
>
> The same comment goes for below kernel-doc functions.
>
> [1] https://www.kernel.org/doc/html/latest/doc-guide/kernel-doc.html#writing-kernel-doc-comments

Thanks for the references/pointers.

>
> > + * Write to a protected SMC register.
> > + * @base: Base address of PMU
> > + * @reg:  Address offset of register
> > + * @val:  Value to write
>
> AFAIR, alignment with spaces is discouraged by kernel coding style.
>
> > + * Return: (0) on success
>
> Not sure if braces are needed around 0 here. Also, is it only 0 value,
> or some other values can be returned?

I don't have access to the bootloader code, but I will try and check this point.

>
> > + *
>
> This line is not needed.

Will fix

>
> > + */
> > +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);
>
> It can be 2 lines instead 4.

Will fix
>
> > +
> > +       if (res.a0)
> > +               pr_warn("%s(): SMC failed: %lu\n", __func__, res.a0);
> > +
> > +       return (int)res.a0;
>
> res.a0 are positive numbers, but in kernel the error codes are usually
> negative numbers. I'm not sure if it's ok to use positive numbers for
> regmap ops, but at least error codes should be documented.

I will see if I can get more information about the error codes
returned. I don't have access to firmware code though so that may not
be possible. The downstream production kernel returned `(int)res.a0`
as an error for functions returning int. So I believe this is fine.

>
> > +}
> > +
> > +/**
> > + * tensor_sec_reg_rmw
> > + * Read/Modify/Write to a protected SMC register.
> > + * @base: Base address of PMU
> > + * @reg:  Address offset of register
>
> @mask is missing? Guess "make W=n" should complain, and kernel-doc too.

Will update to a one line comment as suggested above.

>
> > + * @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;
> > +}
> > +
> > +
>
> Double empty line.

Will fix
>
> > +/*
> > + * 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)) {
>
> Maybe use for_each_set_bit() or something like that?

I'll take a look and see if it looks better.

>
> > +                       if (val & BIT(i)) {
> > +                               offset |= 0xc000;
> > +                               tensor_sec_reg_write(ctx, offset, i);
> > +                       } else {
> > +                               offset |= 0x8000;
>
> Magic number? Maybe makes sense to replace it with a named constant.

Will fix

>
> > +                               tensor_sec_reg_write(ctx, offset, i);
>
> Common line, can be extracted out of if/else block.

Will fix
>
> > +                       }
> > +               }
> > +       }
> > +}
> > +
> > +int tensor_sec_update_bits(void *ctx, unsigned int reg, unsigned int mask, unsigned int val)
>
> Unnecessary exceeds 80 characters-per-line limit.

Will fix
>
> > +{
> > +       int ret = 0;
>
> Why is this needed at all?

I will re-work that to propagate the error from tensor_sec_reg_write()
>
> > +
> > +       /*
> > +        * 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);
>
> Maybe move !np case handling into exynos_get_pmu_regmap_by_phandle()?

I did consider doing that but decided against it. The idea is to have
the same behaviour as syscon_regmap_lookup_by_phandle() and
altr_sysmgr_regmap_lookup_by_phandle().

>
> >         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);
> > +
> > +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;
>
> Why copy that struct? IMHO, either use it as is, or if you want to
> copy it for some particular reason, maybe make pmu_regs_regmap_cfg a
> const?
>
> Also, suggest reducing the variable name length. Maybe regmap_cfg would do?

will fix
>
> >         struct device *dev = &pdev->dev;
> > +       struct device_node *np = dev->of_node;
> >         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")) {
> > +               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;
> > +
> > +               /* 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()? Or even better, return dev_err_probe()?

Will update to dev_err_probe()

>
> > +               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);
>
> Why use "extern" here, it's just a function declaration.

Will fix. I see that mfd/syscon.h is actually declared the same with
extern which is likely why this ended up here.

>
> > +
>
> Either remove this empty line, or add more empty lines around all
> parts of #ifdef block for consistency.

Will fix

regards,

Peter