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

Heiko Stuebner
2022-09-05T14:17:10Z

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;
+ }
+
+ 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