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

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.

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/all/20221011231841.2951264-2-heiko@sntech.de/
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

3 files changed, 47 insertions, 1 deletions

diff --git a/arch/riscv/Kconfig.erratas b/arch/riscv/Kconfig.erratas
index f3623df23b5f..69621ae6d647 100644
--- a/arch/riscv/Kconfig.erratas
+++ b/arch/riscv/Kconfig.erratas
@@ -66,4 +66,17 @@ 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 21546937db39..fac5742d1c1e 100644
--- a/arch/riscv/errata/thead/errata.c
+++ b/arch/riscv/errata/thead/errata.c
@@ -47,6 +47,22 @@ 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)
 {
@@ -58,6 +74,9 @@ 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