Date:   Thu, 6 Oct 2022 20:20:14 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Heiko Stuebner <heiko@...ech.de>
Cc:     atishp@...shpatra.org, anup@...infault.org, will@...nel.org,
        mark.rutland@....com, paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Conor.Dooley@...rochip.com,
        cmuellner@...ux.com, samuel@...lland.org
Subject: Re: [PATCH 2/2] drivers/perf: riscv_pmu_sbi: add support for PMU
 variant on T-Head C9xx cores

On Tue, Oct 04, 2022 at 10:37:24PM +0200, Heiko Stuebner 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@...ech.de>
> ---
>  arch/riscv/Kconfig.erratas           | 13 +++++++++++
>  arch/riscv/errata/thead/errata.c     | 18 +++++++++++++++
>  arch/riscv/include/asm/errata_list.h | 16 +++++++++++++-
>  drivers/perf/riscv_pmu_sbi.c         | 33 +++++++++++++++++++---------
>  4 files changed, 69 insertions(+), 11 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..67fa078f303f 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -47,6 +47,21 @@ 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;

Silly question maybe, but is it worth explaining in a comment why the
archid and impid are zero?

Anyways, on the last version I said:
> modulo Andreas' question being answered satisfactorially, this is:
> Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>

I guess he just never got back about it, so you may apply the R-b I
guess. Your response seems fair to me /shrug.
Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>

Thanks,
Conor.

> +
> +	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 +73,9 @@ 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 8de4ca2fef21..ec0972c7c562 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 +684,17 @@ 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 (IS_ENABLED(CONFIG_ERRATA_THEAD_PMU) &&
> +		   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 +716,7 @@ 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
> 
> 
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> linux-riscv@...ts.infradead.org
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