Re: [PATCH v4 07/13] RISC-V: Move T-Head PMU to CPU feature alternative framework

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On Wed, Nov 22, 2023 at 8:17 PM Yu Chien Peter Lin
<peterlin@xxxxxxxxxxxxx> wrote:
>
> The custom PMU extension aims to support perf event sampling prior
> to the ratification of Sscofpmf. Instead of diverting the bits and
> register reserved for future standard, a set of custom registers is
> added.  Hence, we may consider it as a CPU feature rather than an
> erratum.
>
> T-Head cores need to append "xtheadpmu" to the riscv,isa-extensions
> for each cpu node in device tree, and enable CONFIG_THEAD_CUSTOM_PMU
> for proper functioning as of this commit.
>
> Signed-off-by: Yu Chien Peter Lin <peterlin@xxxxxxxxxxxxx>
> ---
> Hi All,
>
> This is in preparation for introducing other PMU alternative.
> We follow Conor's suggestion [1][2] to use cpu feature alternative
> framework rather than errata, I'm happy to drop the patch if someone
> is willing to take care of this for T-Head's platforms (or sticking
> with CPU errata alternative?)
>
> [1] https://patchwork.kernel.org/project/linux-riscv/patch/20230907021635.1002738-4-peterlin@xxxxxxxxxxxxx/#25503860
> [2] https://patchwork.kernel.org/project/linux-riscv/patch/20231023004100.2663486-8-peterlin@xxxxxxxxxxxxx/#25565650
>
> Changes v1 -> v2:
>   - New patch
> Changes v2 -> v3:
>   - Removed m{vendor/arch/imp}id checks in pmu_sbi_setup_irqs()
> Changes v3 -> v4:
>   - No change
> ---
>  arch/riscv/Kconfig.errata            | 13 -------------
>  arch/riscv/errata/thead/errata.c     | 19 -------------------
>  arch/riscv/include/asm/errata_list.h | 15 +--------------
>  arch/riscv/include/asm/hwcap.h       |  1 +
>  arch/riscv/kernel/cpufeature.c       |  1 +
>  drivers/perf/Kconfig                 | 13 +++++++++++++
>  drivers/perf/riscv_pmu_sbi.c         | 19 ++++++++++++++-----
>  7 files changed, 30 insertions(+), 51 deletions(-)
>
> diff --git a/arch/riscv/Kconfig.errata b/arch/riscv/Kconfig.errata
> index e2c731cfed8c..0d19f47d1018 100644
> --- a/arch/riscv/Kconfig.errata
> +++ b/arch/riscv/Kconfig.errata
> @@ -86,17 +86,4 @@ config ERRATA_THEAD_CMO
>
>           If you don't know what to do here, say "Y".
>
> -config ERRATA_THEAD_PMU
> -       bool "Apply T-Head PMU errata"
> -       depends on ERRATA_THEAD && RISCV_PMU_SBI
> -       default y
> -       help
> -         The T-Head C9xx cores implement a PMU overflow extension very
> -         similar to the core SSCOFPMF extension.
> -
> -         This will apply the overflow errata to handle the non-standard
> -         behaviour via the regular SBI PMU driver and interface.
> -
> -         If you don't know what to do here, say "Y".
> -
>  endmenu # "CPU errata selection"
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index 0554ed4bf087..5de5f7209132 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -53,22 +53,6 @@ static bool errata_probe_cmo(unsigned int stage,
>         return true;
>  }
>
> -static bool errata_probe_pmu(unsigned int stage,
> -                            unsigned long arch_id, unsigned long impid)
> -{
> -       if (!IS_ENABLED(CONFIG_ERRATA_THEAD_PMU))
> -               return false;
> -
> -       /* target-c9xx cores report arch_id and impid as 0 */
> -       if (arch_id != 0 || impid != 0)
> -               return false;
> -
> -       if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
> -               return false;
> -
> -       return true;
> -}
> -
>  static u32 thead_errata_probe(unsigned int stage,
>                               unsigned long archid, unsigned long impid)
>  {
> @@ -80,9 +64,6 @@ static u32 thead_errata_probe(unsigned int stage,
>         if (errata_probe_cmo(stage, archid, impid))
>                 cpu_req_errata |= BIT(ERRATA_THEAD_CMO);
>
> -       if (errata_probe_pmu(stage, archid, impid))
> -               cpu_req_errata |= BIT(ERRATA_THEAD_PMU);
> -
>         return cpu_req_errata;
>  }
>
> diff --git a/arch/riscv/include/asm/errata_list.h b/arch/riscv/include/asm/errata_list.h
> index 4ed21a62158c..9bccc2ba0eb5 100644
> --- a/arch/riscv/include/asm/errata_list.h
> +++ b/arch/riscv/include/asm/errata_list.h
> @@ -25,8 +25,7 @@
>  #ifdef CONFIG_ERRATA_THEAD
>  #define        ERRATA_THEAD_PBMT 0
>  #define        ERRATA_THEAD_CMO 1
> -#define        ERRATA_THEAD_PMU 2
> -#define        ERRATA_THEAD_NUMBER 3
> +#define        ERRATA_THEAD_NUMBER 2
>  #endif
>
>  #ifdef __ASSEMBLY__
> @@ -147,18 +146,6 @@ asm volatile(ALTERNATIVE_2(                                                \
>             "r"((unsigned long)(_start) + (_size))                      \
>         : "a0")
>
> -#define THEAD_C9XX_RV_IRQ_PMU                  17
> -#define THEAD_C9XX_CSR_SCOUNTEROF              0x5c5
> -
> -#define ALT_SBI_PMU_OVERFLOW(__ovl)                                    \
> -asm volatile(ALTERNATIVE(                                              \
> -       "csrr %0, " __stringify(CSR_SSCOUNTOVF),                        \
> -       "csrr %0, " __stringify(THEAD_C9XX_CSR_SCOUNTEROF),             \
> -               THEAD_VENDOR_ID, ERRATA_THEAD_PMU,                      \
> -               CONFIG_ERRATA_THEAD_PMU)                                \
> -       : "=r" (__ovl) :                                                \
> -       : "memory")
> -
>  #endif /* __ASSEMBLY__ */
>
>  #endif
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index 06d30526ef3b..c85ee34c78d9 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -57,6 +57,7 @@
>  #define RISCV_ISA_EXT_ZIHPM            42
>  #define RISCV_ISA_EXT_SMSTATEEN                43
>  #define RISCV_ISA_EXT_ZICOND           44
> +#define RISCV_ISA_EXT_XTHEADPMU                45
>
>  #define RISCV_ISA_EXT_MAX              64
>
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index b3785ffc1570..e606f588d366 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -185,6 +185,7 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
>         __RISCV_ISA_EXT_DATA(svinval, RISCV_ISA_EXT_SVINVAL),
>         __RISCV_ISA_EXT_DATA(svnapot, RISCV_ISA_EXT_SVNAPOT),
>         __RISCV_ISA_EXT_DATA(svpbmt, RISCV_ISA_EXT_SVPBMT),
> +       __RISCV_ISA_EXT_DATA(xtheadpmu, RISCV_ISA_EXT_XTHEADPMU),
>  };
>
>  const size_t riscv_isa_ext_count = ARRAY_SIZE(riscv_isa_ext);
> diff --git a/drivers/perf/Kconfig b/drivers/perf/Kconfig
> index 273d67ecf6d2..c71b6f16bdfa 100644
> --- a/drivers/perf/Kconfig
> +++ b/drivers/perf/Kconfig
> @@ -86,6 +86,19 @@ config RISCV_PMU_SBI
>           full perf feature support i.e. counter overflow, privilege mode
>           filtering, counter configuration.
>
> +config THEAD_CUSTOM_PMU
> +       bool "T-Head custom PMU support"
> +       depends on RISCV_ALTERNATIVE && RISCV_PMU_SBI
> +       default y
> +       help
> +         The T-Head C9xx cores implement a PMU overflow extension very
> +         similar to the core SSCOFPMF extension.
> +
> +         This will patch the overflow CSR and handle the non-standard
> +         behaviour via the regular SBI PMU driver and interface.
> +
> +         If you don't know what to do here, say "Y".
> +
>  config ARM_PMU_ACPI
>         depends on ARM_PMU && ACPI
>         def_bool y
> diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> index 2edbc37abadf..31ca79846399 100644
> --- a/drivers/perf/riscv_pmu_sbi.c
> +++ b/drivers/perf/riscv_pmu_sbi.c
> @@ -20,10 +20,21 @@
>  #include <linux/cpu_pm.h>
>  #include <linux/sched/clock.h>
>
> -#include <asm/errata_list.h>
>  #include <asm/sbi.h>
>  #include <asm/cpufeature.h>
>
> +#define THEAD_C9XX_RV_IRQ_PMU          17
> +#define THEAD_C9XX_CSR_SCOUNTEROF      0x5c5
> +
> +#define ALT_SBI_PMU_OVERFLOW(__ovl)                                    \
> +asm volatile(ALTERNATIVE(                                              \
> +       "csrr %0, " __stringify(CSR_SSCOUNTOVF),                        \
> +       "csrr %0, " __stringify(THEAD_C9XX_CSR_SCOUNTEROF),             \
> +               0, RISCV_ISA_EXT_XTHEADPMU,                             \
> +               CONFIG_THEAD_CUSTOM_PMU)                                \
> +       : "=r" (__ovl) :                                                \
> +       : "memory")
> +
>  #define SYSCTL_NO_USER_ACCESS  0
>  #define SYSCTL_USER_ACCESS     1
>  #define SYSCTL_LEGACY          2
> @@ -808,10 +819,8 @@ static int pmu_sbi_setup_irqs(struct riscv_pmu *pmu, struct platform_device *pde
>         if (riscv_isa_extension_available(NULL, SSCOFPMF)) {
>                 riscv_pmu_irq_num = RV_IRQ_PMU;
>                 riscv_pmu_use_irq = true;
> -       } else if (IS_ENABLED(CONFIG_ERRATA_THEAD_PMU) &&
> -                  riscv_cached_mvendorid(0) == THEAD_VENDOR_ID &&
> -                  riscv_cached_marchid(0) == 0 &&
> -                  riscv_cached_mimpid(0) == 0) {
> +       } else if (riscv_isa_extension_available(NULL, XTHEADPMU) &&
> +                  IS_ENABLED(CONFIG_THEAD_CUSTOM_PMU)) {
>                 riscv_pmu_irq_num = THEAD_C9XX_RV_IRQ_PMU;
>                 riscv_pmu_use_irq = true;
>         }
> --
> 2.34.1
>
Reviewed-by: Guo Ren <guoren@xxxxxxxxxx>

-- 
Best Regards
 Guo Ren





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