Re: [PATCH 4/4] RISC-V: add support for vendor-extensions via AT_BASE_PLATFORM and xthead

[Andrew Jones]

On Mon, Apr 24, 2023 at 09:49:11PM +0200, Heiko Stuebner wrote:
> From: Heiko Stuebner <heiko.stuebner@xxxxxxxx>
> 
> T-Head cores support a number of own ISA extensions that also include
> optimized instructions which could benefit userspace to improve
> performance.
> 
> Extensions supported by current T-Head cores are:
> * XTheadBa - bitmanipulation instructions for address calculation
> * XTheadBb - conditional basic bit-manipulation instructions
> * XTheadBs - instructions to access a single bit in a register
> * XTheadCmo - cache management operations
> * XTheadCondMov - conditional move instructions
> * XTheadFMemIdx - indexed memory operations for floating-point registers
> * XTheadFmv - double-precision floating-point high-bit data transmission
>               intructions for RV32
> * XTheadInt - instructions to reduce the code size of ISRs and/or the
>               interrupt latencies that are caused by ISR entry/exit code
> * XTheadMac - multiply-accumulate instructions
> * XTheadMemIdx - indexed memory operations for GP registers
> * XTheadMemPair - two-GPR memory operations
> * XTheadSync - multi-core synchronization instructions
> 
> In-depth descriptions of these extensions can be found on
>     https://github.com/T-head-Semi/thead-extension-spec
> 
> Support for those extensions was merged into the relevant toolchains
> so userspace programs can select necessary optimizations when needed.
> 
> So a mechanism to the isa-string generation to export vendor-extension
> lists via the errata mechanism and implement it for T-Head C9xx cores.
> 
> This exposes these vendor extensions then both in AT_BASE_PLATFORM
> and /proc/cpuinfo.
> 
> Signed-off-by: Heiko Stuebner <heiko.stuebner@xxxxxxxx>
> ---
>  arch/riscv/errata/thead/errata.c     | 43 ++++++++++++++++++++++++++++
>  arch/riscv/include/asm/alternative.h |  4 +++
>  arch/riscv/kernel/alternative.c      | 21 ++++++++++++++
>  arch/riscv/kernel/cpu.c              | 12 ++++++++
>  4 files changed, 80 insertions(+)
> 
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index 1036b8f933ec..eb635bf80737 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -15,6 +15,7 @@
>  #include <asm/errata_list.h>
>  #include <asm/hwprobe.h>
>  #include <asm/patch.h>
> +#include <asm/switch_to.h>
>  #include <asm/vendorid_list.h>
>  
>  static bool errata_probe_pbmt(unsigned int stage,
> @@ -125,3 +126,45 @@ void __init_or_module thead_feature_probe_func(unsigned int cpu,
>  	if ((archid == 0) && (impid == 0))
>  		per_cpu(misaligned_access_speed, cpu) = RISCV_HWPROBE_MISALIGNED_FAST;
>  }
> +
> +
> +char *thead_extension_list_func(unsigned long archid,
> +				unsigned long impid)
> +{
> +	if ((archid == 0) && (impid == 0)) {
> +		const char *xbase1 = "xtheadba_xtheadbb_xtheadbs_xtheadcmo_xtheadcondmov";
> +		const char *xbase2 = "_xtheadint_xtheadmac_xtheadmemidx_xtheadmempair_xtheadsync";
> +		const char *xfpu = "_xtheadfmemIdx";
> +#ifdef CONFIG_32BIT
> +		const char *xfpu32 = "_xtheadfmv";
> +#endif
> +		int len = strlen(xbase1) + strlen(xbase2);
> +		char *str;
> +
> +		if (has_fpu()) {
> +			len += strlen(xfpu);
> +#ifdef CONFIG_32BIT
> +			len+= strlen(xfpu32);
> +#endif
> +		}
> +
> +		str = kzalloc(len, GFP_KERNEL);
> +		if (!str)
> +			return str;
> +
> +		strcpy(str, xbase1);
> +
> +		if (has_fpu()) {
> +			strcat(str, xfpu);
> +#ifdef CONFIG_32BIT
> +			strcat(str, xfpu32);
> +#endif
> +		}
> +
> +		strcat(str, xbase2);
> +
> +		return str;
> +	}
> +
> +	return NULL;
> +}
> diff --git a/arch/riscv/include/asm/alternative.h b/arch/riscv/include/asm/alternative.h
> index a8f5cf6694a1..8c9aec196649 100644
> --- a/arch/riscv/include/asm/alternative.h
> +++ b/arch/riscv/include/asm/alternative.h
> @@ -31,6 +31,7 @@
>  #define ALT_ALT_PTR(a)			__ALT_PTR(a, alt_offset)
>  
>  void __init probe_vendor_features(unsigned int cpu);
> +char *list_vendor_extensions(void);
>  void __init apply_boot_alternatives(void);
>  void __init apply_early_boot_alternatives(void);
>  void apply_module_alternatives(void *start, size_t length);
> @@ -55,6 +56,8 @@ void thead_errata_patch_func(struct alt_entry *begin, struct alt_entry *end,
>  
>  void thead_feature_probe_func(unsigned int cpu, unsigned long archid,
>  			      unsigned long impid);
> +char *thead_extension_list_func(unsigned long archid,
> +				unsigned long impid);
>  
>  void riscv_cpufeature_patch_func(struct alt_entry *begin, struct alt_entry *end,
>  				 unsigned int stage);
> @@ -62,6 +65,7 @@ void riscv_cpufeature_patch_func(struct alt_entry *begin, struct alt_entry *end,
>  #else /* CONFIG_RISCV_ALTERNATIVE */
>  
>  static inline void probe_vendor_features(unsigned int cpu) { }
> +static inline char *list_vendor_extensions(void) { return NULL; }
>  static inline void apply_boot_alternatives(void) { }
>  static inline void apply_early_boot_alternatives(void) { }
>  static inline void apply_module_alternatives(void *start, size_t length) { }
> diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
> index fc65c9293ac5..18913fd1809f 100644
> --- a/arch/riscv/kernel/alternative.c
> +++ b/arch/riscv/kernel/alternative.c
> @@ -29,6 +29,8 @@ struct cpu_manufacturer_info_t {
>  				  unsigned int stage);
>  	void (*feature_probe_func)(unsigned int cpu, unsigned long archid,
>  				   unsigned long impid);
> +	char *(*extension_list_func)(unsigned long archid,
> +				    unsigned long impid);
>  };
>  
>  static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_info_t *cpu_mfr_info)
> @@ -54,6 +56,7 @@ static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_inf
>  	case THEAD_VENDOR_ID:
>  		cpu_mfr_info->patch_func = thead_errata_patch_func;
>  		cpu_mfr_info->feature_probe_func = thead_feature_probe_func;
> +		cpu_mfr_info->extension_list_func = thead_extension_list_func;
>  		break;
>  #endif
>  	default:
> @@ -157,6 +160,24 @@ void __init_or_module probe_vendor_features(unsigned int cpu)
>  					cpu_mfr_info.imp_id);
>  }
>  
> +/*
> + * Lists the vendor-specific extensions common to all cores.
> + * Returns a new underscore "_" concatenated string that the
> + * caller is supposed to free after use.
> + */
> +char *list_vendor_extensions(void)
> +{
> +	struct cpu_manufacturer_info_t cpu_mfr_info;
> +
> +	riscv_fill_cpu_mfr_info(&cpu_mfr_info);
> +	if (!cpu_mfr_info.extension_list_func)
> +		return NULL;
> +
> +	return cpu_mfr_info.extension_list_func(cpu_mfr_info.arch_id,
> +						cpu_mfr_info.imp_id);
> +
> +}
> +
>  /*
>   * This is called very early in the boot process (directly after we run
>   * a feature detect on the boot CPU). No need to worry about other CPUs
> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index 71770563199f..6a0a45b2eb20 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -7,6 +7,7 @@
>  #include <linux/init.h>
>  #include <linux/seq_file.h>
>  #include <linux/of.h>
> +#include <asm/alternative.h>
>  #include <asm/cpufeature.h>
>  #include <asm/csr.h>
>  #include <asm/hwcap.h>
> @@ -260,6 +261,7 @@ static char *riscv_create_isa_string(void)
>  {
>  	int maxlen = 4;
>  	char *isa_str;
> +	char *vendor_isa;
>  	int i;
>  
>  	/* calculate the needed string length */
> @@ -268,6 +270,10 @@ static char *riscv_create_isa_string(void)
>  			maxlen++;
>  	maxlen += strlen_isa_ext();
>  
> +	vendor_isa = list_vendor_extensions();
> +	if (vendor_isa)
> +		maxlen += strlen(vendor_isa) + 1;
> +
>  	isa_str = kzalloc(maxlen, GFP_KERNEL);
>  	if (!isa_str)
>  		return ERR_PTR(-ENOMEM);
> @@ -287,6 +293,12 @@ static char *riscv_create_isa_string(void)
>  
>  	strcat_isa_ext(isa_str);
>  
> +	if(vendor_isa) {
          ^ need a space

> +		strcat(isa_str, "_");
> +		strcat(isa_str, vendor_isa);
> +		kfree(vendor_isa);
> +	}
> +
>  	return isa_str;
>  }
>  
> -- 
> 2.39.0
>

For the extension of riscv_create_isa_string to support vendor lists,

Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>