Re: [PATCH v3] drivers/perf: riscv_pmu_sbi: add support for PMU variant on T-Head C9xx cores

Heiko Stübner
2022-09-07T17:57:47Z

Am Montag, 5. September 2022, 16:16:44 CEST schrieb Heiko Stuebner:
> With the T-HEAD C9XX cores being designed before or during the ratification
> to the SSCOFPMF extension, it implements functionality very similar but
> not equal to it.
>
> It implements overflow handling and also some privilege-mode filtering.
> While SSCOFPMF supports this for all modes, the C9XX only implements the
> filtering for M-mode and S-mode but not user-mode.
>
> So add some adaptions to allow the C9XX to still handle
> its PMU through the regular SBI PMU interface instead of defining new
> interfaces or drivers.
>
> To work properly, this requires a matching change in SBI, though the actual
> interface between kernel and SBI does not change.
>
> The main differences are a the overflow CSR and irq number.
>
> As the reading of the overflow-csr is in the hot-path during irq handling,
> use an errata and alternatives to not introduce new conditionals there.
>
> Signed-off-by: Heiko Stuebner <heiko@sntech.de>
> ---
> changes in v3:
> - improve commit message (Atish, Conor)
> - IS_ENABLED and BIT() in errata probe (Conor)
>
> The change depends on my cpufeature/t-head errata probe cleanup series [1].
>
>
> changes in v2:
> - use alternatives for the CSR access
> - make the irq num selection a bit nicer
>
> There is of course a matching opensbi-part whose current implementation can
> be found on [0], but as comments show, this needs some more work still.
>
>
> [0] https://patchwork.ozlabs.org/project/opensbi/cover/20220817112004.745776-1-heiko@sntech.de/
> [1] https://lore.kernel.org/all/20220905111027.2463297-1-heiko@sntech.de/
>
> arch/riscv/Kconfig.erratas | 14 ++++++++++++
> arch/riscv/errata/thead/errata.c | 18 ++++++++++++++++
> arch/riscv/include/asm/errata_list.h | 16 +++++++++++++-
> drivers/perf/riscv_pmu_sbi.c | 32 +++++++++++++++++++---------
> 4 files changed, 69 insertions(+), 11 deletions(-)
>
> diff --git a/arch/riscv/Kconfig.erratas b/arch/riscv/Kconfig.erratas
> index 6850e9389930..f1eaac4c0073 100644
> --- a/arch/riscv/Kconfig.erratas
> +++ b/arch/riscv/Kconfig.erratas
> @@ -66,4 +66,18 @@ 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
> + depends on RISCV_PMU_SBI

as suggested by Conor in another thread, this should probably be
depends on ERRATA_THEAD && RISCV_PMU_SBI

in a single line

> + 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 902e12452821..d4b1526538ad 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -46,6 +46,21 @@ 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;
> +
> + 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)
> {
> @@ -57,6 +72,9 @@ 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 19a771085781..4180312d2a70 100644
> --- a/arch/riscv/include/asm/errata_list.h
> +++ b/arch/riscv/include/asm/errata_list.h
> @@ -6,6 +6,7 @@
> #define ASM_ERRATA_LIST_H
>
> #include <asm/alternative.h>
> +#include <asm/csr.h>
> #include <asm/vendorid_list.h>
>
> #ifdef CONFIG_ERRATA_SIFIVE
> @@ -17,7 +18,8 @@
> #ifdef CONFIG_ERRATA_THEAD
> #define ERRATA_THEAD_PBMT 0
> #define ERRATA_THEAD_CMO 1
> -#define ERRATA_THEAD_NUMBER 2
> +#define ERRATA_THEAD_PMU 2
> +#define ERRATA_THEAD_NUMBER 3
> #endif
>
> #define CPUFEATURE_SVPBMT 0
> @@ -142,6 +144,18 @@ 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/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> index 6f6681bbfd36..f814d3ce5ba2 100644
> --- a/drivers/perf/riscv_pmu_sbi.c
> +++ b/drivers/perf/riscv_pmu_sbi.c
> @@ -19,6 +19,7 @@
> #include <linux/of.h>
> #include <linux/cpu_pm.h>
>
> +#include <asm/errata_list.h>
> #include <asm/sbi.h>
> #include <asm/hwcap.h>
>
> @@ -46,6 +47,8 @@ static const struct attribute_group *riscv_pmu_attr_groups[] = {
> * per_cpu in case of harts with different pmu counters
> */
> static union sbi_pmu_ctr_info *pmu_ctr_list;
> +static bool riscv_pmu_use_irq;
> +static unsigned int riscv_pmu_irq_num;
> static unsigned int riscv_pmu_irq;
>
> struct sbi_pmu_event_data {
> @@ -575,7 +578,7 @@ static irqreturn_t pmu_sbi_ovf_handler(int irq, void *dev)
> fidx = find_first_bit(cpu_hw_evt->used_hw_ctrs, RISCV_MAX_COUNTERS);
> event = cpu_hw_evt->events[fidx];
> if (!event) {
> - csr_clear(CSR_SIP, SIP_LCOFIP);
> + csr_clear(CSR_SIP, BIT(riscv_pmu_irq_num));
> return IRQ_NONE;
> }
>
> @@ -583,13 +586,13 @@ static irqreturn_t pmu_sbi_ovf_handler(int irq, void *dev)
> pmu_sbi_stop_hw_ctrs(pmu);
>
> /* Overflow status register should only be read after counter are stopped */
> - overflow = csr_read(CSR_SSCOUNTOVF);
> + ALT_SBI_PMU_OVERFLOW(overflow);
>
> /*
> * Overflow interrupt pending bit should only be cleared after stopping
> * all the counters to avoid any race condition.
> */
> - csr_clear(CSR_SIP, SIP_LCOFIP);
> + csr_clear(CSR_SIP, BIT(riscv_pmu_irq_num));
>
> /* No overflow bit is set */
> if (!overflow)
> @@ -651,10 +654,10 @@ static int pmu_sbi_starting_cpu(unsigned int cpu, struct hlist_node *node)
> /* Stop all the counters so that they can be enabled from perf */
> pmu_sbi_stop_all(pmu);
>
> - if (riscv_isa_extension_available(NULL, SSCOFPMF)) {
> + if (riscv_pmu_use_irq) {
> cpu_hw_evt->irq = riscv_pmu_irq;
> - csr_clear(CSR_IP, BIT(RV_IRQ_PMU));
> - csr_set(CSR_IE, BIT(RV_IRQ_PMU));
> + csr_clear(CSR_IP, BIT(riscv_pmu_irq_num));
> + csr_set(CSR_IE, BIT(riscv_pmu_irq_num));
> enable_percpu_irq(riscv_pmu_irq, IRQ_TYPE_NONE);
> }
>
> @@ -663,9 +666,9 @@ static int pmu_sbi_starting_cpu(unsigned int cpu, struct hlist_node *node)
>
> static int pmu_sbi_dying_cpu(unsigned int cpu, struct hlist_node *node)
> {
> - if (riscv_isa_extension_available(NULL, SSCOFPMF)) {
> + if (riscv_pmu_use_irq) {
> disable_percpu_irq(riscv_pmu_irq);
> - csr_clear(CSR_IE, BIT(RV_IRQ_PMU));
> + csr_clear(CSR_IE, BIT(riscv_pmu_irq_num));
> }
>
> /* Disable all counters access for user mode now */
> @@ -681,7 +684,16 @@ static int pmu_sbi_setup_irqs(struct riscv_pmu *pmu, struct platform_device *pde
> struct device_node *cpu, *child;
> struct irq_domain *domain = NULL;
>
> - if (!riscv_isa_extension_available(NULL, SSCOFPMF))
> + if (riscv_isa_extension_available(NULL, SSCOFPMF)) {
> + riscv_pmu_irq_num = RV_IRQ_PMU;
> + riscv_pmu_use_irq = true;
> + } else if (sbi_get_mvendorid() == THEAD_VENDOR_ID &&
> + sbi_get_marchid() == 0 && sbi_get_mimpid() == 0) {
> + riscv_pmu_irq_num = THEAD_C9XX_RV_IRQ_PMU;
> + riscv_pmu_use_irq = true;
> + }
> +
> + if (!riscv_pmu_use_irq)
> return -EOPNOTSUPP;
>
> for_each_of_cpu_node(cpu) {
> @@ -703,7 +715,7 @@ static int pmu_sbi_setup_irqs(struct riscv_pmu *pmu, struct platform_device *pde
> return -ENODEV;
> }
>
> - riscv_pmu_irq = irq_create_mapping(domain, RV_IRQ_PMU);
> + riscv_pmu_irq = irq_create_mapping(domain, riscv_pmu_irq_num);
> if (!riscv_pmu_irq) {
> pr_err("Failed to map PMU interrupt for node\n");
> return -ENODEV;
>