Re: [PATCH v7 07/16] RISC-V: Move T-Head PMU to CPU feature alternative framework

[Anup Patel <apatel@ventanamicro.com>]

On Wed, Jan 17, 2024 at 2:26 AM Atish Patra <atishp@atishpatra.org> wrote:
>
> On Tue, Jan 9, 2024 at 11:40 PM Yu Chien Peter Lin
> <peterlin@andestech.com> 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.
> >
>
> I don't think we should do that. Any custom implementation that
> violates the standard RISC-V spec should
> be an errata not a feature.
> As per my understanding, a vendor can call an extension custom ISA
> extension if the same feature is not available
> in the standard ISA extensions or the mechanism is completely
> different. It must also not violate any standard spec as well.

I agree with Atish here. There is a well defined encoding space for
custom extensions.

If a custom extension spills over to standard encoding space then
it should be treated as an errata and not a proper custom extension.

>
> In this case, a standard sscofpmf is already available. Moreover, both
> Andes and T-head extensions violate the standard
> spec by reusing local interrupt numbers (17(Thead) & 18(Andes)) which
> are clearly specified as reserved for standard local interrupts
> in the AIA specification.
>
> Please implementation Andes PMU support as an errata as well similar to T-head
>
>
> > 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.

T-Head has many violations of using standard encoding space. I don't see
why this series should be touching T-Head erratas.

If Andes custom PMU CSRs are defined in custom encoding space then
Andes PMU can be treated as proper custom extension.

Regards,
Anup

> >
> > Signed-off-by: Yu Chien Peter Lin <peterlin@andestech.com>
> > Reviewed-by: Guo Ren <guoren@kernel.org>
> > Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
> > ---
> > 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
> > Changes v4 -> v5:
> >   - Include Guo's Reviewed-by
> >   - Let THEAD_CUSTOM_PMU depend on ARCH_THEAD
> > Changes v5 -> v6:
> >   - Include Conor's Reviewed-by
> > Changes v6 -> v7:
> >   - 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 5340f818746b..480f9da7fba7 100644
> > --- a/arch/riscv/include/asm/hwcap.h
> > +++ b/arch/riscv/include/asm/hwcap.h
> > @@ -80,6 +80,7 @@
> >  #define RISCV_ISA_EXT_ZFA              71
> >  #define RISCV_ISA_EXT_ZTSO             72
> >  #define RISCV_ISA_EXT_ZACAS            73
> > +#define RISCV_ISA_EXT_XTHEADPMU                74
> >
> >  #define RISCV_ISA_EXT_MAX              128
> >  #define RISCV_ISA_EXT_INVALID          U32_MAX
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index e32591e9da90..4aded5bf8fc3 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -303,6 +303,7 @@ 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..6cef15ec7c25 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 ARCH_THEAD && 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
> >
>
>
> --
> Regards,
> Atish
>
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