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

Atish Patra
2022-09-07T23:15:17Z

On Wed, Sep 7, 2022 at 4:09 PM Atish Patra <atishp@atishpatra.org> wrote:
>
>
>
> On Mon, Sep 5, 2022 at 7:16 AM Heiko Stuebner <heiko@sntech.de> wrote:
>>
>> 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
>> + 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;
>> + }
>> +
>
>

Resending my response as gmail automatically switched compose format
to HTML for some reason.
Apologies for the spam.

We already have all the vendorid/marchid/mimipid information available
from the errata framework.
Can we just get these from errata instead of making another 3 SBI calls ?

Another option is that Anup's /proc/cpuinfo patch also makes the same
SBI calls. Maybe cache these three
information in the SBI layer so that all other arch code can invoke that.

I also think this else check should be part of the config ERRATA_THEAD_PMU.

>
>>
>> + 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;
>> --
>> 2.35.1
>>
>
>
> --
> Regards,
> Atish

--
Regards,
Atish