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From: Peter Griffin <peter.griffin@linaro.org>
Date: Wed, 24 Jan 2024 10:41:16 +0000
Message-ID: <CADrjBPqTqe+HDN_ye41sR_yJgnUXOWwkZsQyujptPPfzg+EBeg@mail.gmail.com>
Subject: Re: [PATCH 2/9] soc: samsung: exynos-pmu: Add exynos_pmu_update/read/write
 APIs and SoC quirks
To: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: arnd@arndb.de, robh+dt@kernel.org, krzysztof.kozlowski+dt@linaro.org, 
	linux@roeck-us.net, wim@linux-watchdog.org, conor+dt@kernel.org, 
	alim.akhtar@samsung.com, jaewon02.kim@samsung.com, chanho61.park@samsung.com, 
	semen.protsenko@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, 
	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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Hi Krzysztof,

Thanks for the review feedback.

On Tue, 23 Jan 2024 at 11:17, Krzysztof Kozlowski
<krzysztof.kozlowski@linaro.org> wrote:
>
> On 22/01/2024 23:57, Peter Griffin wrote:
> > Newer Exynos SoCs have atomic set/clear bit hardware for PMU registers as
> > these registers can be accessed by multiple masters. Some platforms also
> > protect the PMU registers for security hardening reasons so they can't be
> > written by normal world and are only write acessible in el3 via a SMC call.
>
>
> Typo? accessible?

Will fix in v2.
>
> >
> > Add support for both of these usecases using SoC specific quirks that are
> > determined from the DT compatible string.>
> > Drivers which need to read and write PMU registers should now use these
> > new exynos_pmu_*() APIs instead of obtaining a regmap using
> > syscon_regmap_lookup_by_phandle()
> >
> > Depending on the SoC specific quirks, the exynos_pmu_*() APIs will access
> > the PMU register in the appropriate way.
> >
> > Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
> > ---
> >  drivers/soc/samsung/exynos-pmu.c       | 209 ++++++++++++++++++++++++-
> >  drivers/soc/samsung/exynos-pmu.h       |   4 +
> >  include/linux/soc/samsung/exynos-pmu.h |  28 ++++
> >  3 files changed, 234 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/soc/samsung/exynos-pmu.c b/drivers/soc/samsung/exynos-pmu.c
> > index 250537d7cfd6..e9e933ede568 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>
> > @@ -12,29 +13,204 @@
> >  #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"
> >
> > +/**
> > + * DOC: Quirk flags for different Exynos PMU IP-cores
> > + *
> > + * This driver supports multiple Exynos based SoCs, each of which might have a
> > + * different set of registers and features supported.
> > + *
> > + * Quirk flags described below serve the purpose of telling the driver about
> > + * mentioned SoC traits, and can be specified in driver data for each particular
> > + * supported device.
> > + *
> > + * %QUIRK_HAS_ATOMIC_BITSETHW: PMU IP has special atomic bit set/clear HW
> > + * to protect against PMU registers being accessed from multiple bus masters.
> > + *
> > + * %QUIRK_PMU_ALIVE_WRITE_SEC: PMU registers are *not* write accesible from
> > + * normal world. This is found on some SoCs as a security hardening measure. PMU
> > + * registers on these SoCs can only be written via a SMC call and registers are
> > + * checked by EL3 firmware against an allowlist before the write can procede.
> > + * Note: This quirk should only be set for platforms whose el3 firmware
> > + * implements the TENSOR_SMC_PMU_SEC_REG interface below.
> > + */
> > +
> > +#define QUIRK_HAS_ATOMIC_BITSETHW            BIT(0)
> > +#define QUIRK_PMU_ALIVE_WRITE_SEC            BIT(1)
> > +
> > +#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;
> > +     phys_addr_t pmu_base_pa;
> > +     /* protect PMU reg atomic update operations */
> > +     spinlock_t update_lock;
> >  };
> >
> > -void __iomem *pmu_base_addr;
> >  static struct exynos_pmu_context *pmu_context;
> >
> > +/*
> > + * Some 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
>
> These are tensor specific...
>
> > +
> > +int set_priv_reg(phys_addr_t reg, u32 val)
>
> ...but this not...
>
> > +{
> > +     struct arm_smccc_res res;
> > +
> > +     arm_smccc_smc(TENSOR_SMC_PMU_SEC_REG,
>
> ... and this is again.
>
> Some naming should be clarified, e.g. tensor specific functions should
> have some prefix as well, e.g. tensor_writel(), tensor_cmpxchg() or
> something similar.

Noted. I will add a tensor prefix on these two functions as well in v2.

>
>
> > +                   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;
> > +}
> > +
> > +int rmw_priv_reg(phys_addr_t reg, u32 mask, u32 val)
> > +{
> > +     struct arm_smccc_res res;
> > +
> > +     arm_smccc_smc(TENSOR_SMC_PMU_SEC_REG,
> > +                   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;
> > +}
> > +
> > +/*
> > + * For SoCs that have set/clear bit hardware (as indicated by
> > + * QUIRK_HAS_ATOMIC_BITSETHW) 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
> > + * exynos_pmu_set_bit_atomic(0x3e80, 0x3f00, 0x3f00);
> > + *
> > + * To clear bits 13:8 in PMU offset 0x3e80
> > + * exynos_pmu_set_bit_atomic(0x3e80, 0x0, 0x3f00);
> > + */
> > +static inline void exynos_pmu_set_bit_atomic(unsigned int offset,
> > +                                          u32 val, u32 mask)
> > +{
> > +     unsigned long flags;
> > +     unsigned int i;
> > +
> > +     spin_lock_irqsave(&pmu_context->update_lock, flags);
> > +     for (i = 0; i < 32; i++) {
> > +             if (mask & BIT(i)) {
> > +                     if (val & BIT(i)) {
> > +                             offset |= 0xc000;
> > +                             pmu_raw_writel(i, offset);
> > +                     } else {
> > +                             offset |= 0x8000;
> > +                             pmu_raw_writel(i, offset);
> > +                     }
> > +             }
> > +     }
> > +     spin_unlock_irqrestore(&pmu_context->update_lock, flags);
> > +}
> > +
> > +int exynos_pmu_update_bits(unsigned int offset, unsigned int mask,
> > +                        unsigned int val)
> > +{
> > +     if (pmu_context->pmu_data &&
> > +         pmu_context->pmu_data->quirks & QUIRK_PMU_ALIVE_WRITE_SEC)
> > +             return rmw_priv_reg(pmu_context->pmu_base_pa + offset,
> > +                                 mask, val);
> > +
> > +     return regmap_update_bits(pmu_context->pmureg, offset, mask, val);
> > +}
> > +EXPORT_SYMBOL(exynos_pmu_update_bits);
>
> You need kerneldoc for all exported functions.
>
> Also, EXPORT_SYMBOL_GPL

Will fix both in v2.

>
> > +
> >  void pmu_raw_writel(u32 val, u32 offset)
> >  {
> > -     writel_relaxed(val, pmu_base_addr + offset);
> > +     if (pmu_context->pmu_data &&
> > +         pmu_context->pmu_data->quirks & QUIRK_PMU_ALIVE_WRITE_SEC)
> > +             return (void)set_priv_reg(pmu_context->pmu_base_pa + offset,
> > +                                       val);
> > +
> > +     return writel_relaxed(val, pmu_context->pmu_base_addr + offset);
> >  }
> >
>
> ...
>
> > diff --git a/drivers/soc/samsung/exynos-pmu.h b/drivers/soc/samsung/exynos-pmu.h
> > index 1c652ffd79b4..570c6e4dc8c3 100644
> > --- a/drivers/soc/samsung/exynos-pmu.h
> > +++ b/drivers/soc/samsung/exynos-pmu.h
> > @@ -25,8 +25,12 @@ struct exynos_pmu_data {
> >       void (*pmu_init)(void);
> >       void (*powerdown_conf)(enum sys_powerdown);
> >       void (*powerdown_conf_extra)(enum sys_powerdown);
> > +     u32 quirks;
> >  };
> >
> > +int set_priv_reg(phys_addr_t reg, u32 val);
> > +int rmw_priv_reg(phys_addr_t reg, u32 mask, u32 val);
>
> Why these are in the header?

Will fix in v2.

regards,

Peter.