linux-kernel - Re: [PATCH 2/2] riscv: implement cache-management errata for T-Head SoCs

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Message-ID: <mhng-3c71e6fc-cd1c-4796-8b50-6768485b8f4a@palmer-ri-x1c9>
Date:   Wed, 30 Mar 2022 19:30:36 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     heiko@...ech.de
CC:     Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        wefu@...hat.com, guoren@...nel.org, atishp@...shpatra.org,
        anup@...infault.org, mick@....forth.gr, samuel@...lland.org,
        cmuellner@...ux.com, philipp.tomsich@...ll.eu, heiko@...ech.de
Subject:     Re: [PATCH 2/2] riscv: implement cache-management errata for T-Head SoCs

On Mon, 07 Mar 2022 14:46:20 PST (-0800), heiko@...ech.de wrote:
> The T-Head C906 and C910 implement a scheme for handling
> cache operations different from the generic Zicbom extension.
>
> Add an errata for it next to the generic dma coherency ops.
>
> Signed-off-by: Heiko Stuebner <heiko@...ech.de>
> ---
>  arch/riscv/Kconfig.erratas           | 10 +++++++
>  arch/riscv/errata/thead/errata.c     |  5 ++++
>  arch/riscv/include/asm/errata_list.h | 45 ++++++++++++++++++++++++++--
>  3 files changed, 57 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/Kconfig.erratas b/arch/riscv/Kconfig.erratas
> index de4002baa1d0..89a6dcb8ac2a 100644
> --- a/arch/riscv/Kconfig.erratas
> +++ b/arch/riscv/Kconfig.erratas
> @@ -50,4 +50,14 @@ config ERRATA_THEAD_PBMT
>
>  	  If you don't know what to do here, say "Y".
>
> +config ERRATA_THEAD_CMO
> +	bool "Apply T-Head cache management errata"
> +	depends on ERRATA_THEAD && RISCV_DMA_NONCOHERENT
> +	default y
> +	help
> +	  This will apply the cache management errata to handle the
> +	  non-standard handling on non-coherent operations on T-Head SoCs.
> +
> +	  If you don't know what to do here, say "Y".
> +
>  endmenu
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index fd8e0538a3f0..11c26c37425f 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -33,6 +33,11 @@ static const struct errata_info errata_list[ERRATA_THEAD_NUMBER] = {
>  		.stage = RISCV_ALTERNATIVES_EARLY_BOOT,
>  		.check_func = errata_mt_check_func
>  	},
> +	{
> +		.name = "cache-management",
> +		.stage = RISCV_ALTERNATIVES_BOOT,
> +		.check_func = errata_mt_check_func
> +	},
>  };
>
>  static u32 thead_errata_probe(unsigned int stage, unsigned long archid, unsigned long impid)
> diff --git a/arch/riscv/include/asm/errata_list.h b/arch/riscv/include/asm/errata_list.h
> index 7a2dd61af24d..f7c6805daeab 100644
> --- a/arch/riscv/include/asm/errata_list.h
> +++ b/arch/riscv/include/asm/errata_list.h
> @@ -16,7 +16,8 @@
>
>  #ifdef CONFIG_ERRATA_THEAD
>  #define	ERRATA_THEAD_PBMT 0
> -#define	ERRATA_THEAD_NUMBER 1
> +#define	ERRATA_THEAD_CMO 1
> +#define	ERRATA_THEAD_NUMBER 2
>  #endif
>
>  #define	CPUFEATURE_SVPBMT 0
> @@ -104,8 +105,37 @@ asm volatile(ALTERNATIVE(								\
>  #define CBO_CLEAN_A0	".long 0x25200F"
>  #define CBO_FLUSH_A0	".long 0x05200F"
>
> +/*
> + * dcache.ipa rs1 (invalidate, physical address)
> + * | 31 - 25 | 24 - 20 | 19 - 15 | 14 - 12 | 11 - 7 | 6 - 0 |
> + *   0000001    01010      rs1       000      00000  0001011
> + * dache.iva rs1 (invalida, virtual address)
> + *   0000001    00110      rs1       000      00000  0001011
> + *
> + * dcache.cpa rs1 (clean, physical address)
> + * | 31 - 25 | 24 - 20 | 19 - 15 | 14 - 12 | 11 - 7 | 6 - 0 |
> + *   0000001    01001      rs1       000      00000  0001011
> + * dcache.cva rs1 (clean, virtual address)
> + *   0000001    00100      rs1       000      00000  0001011
> + *
> + * dcache.cipa rs1 (clean then invalidate, physical address)
> + * | 31 - 25 | 24 - 20 | 19 - 15 | 14 - 12 | 11 - 7 | 6 - 0 |
> + *   0000001    01011      rs1       000      00000  0001011
> + * dcache.civa rs1 (... virtual address)
> + *   0000001    00111      rs1       000      00000  0001011
> + *
> + * sync.s (make sure all cache operations finished)
> + * | 31 - 25 | 24 - 20 | 19 - 15 | 14 - 12 | 11 - 7 | 6 - 0 |
> + *   0000000    11001     00000      000      00000  0001011
> + */
> +#define THEAD_INVAL_A0	".long 0x0265000b"
> +#define THEAD_CLEAN_A0	".long 0x0245000b"
> +#define THEAD_FLUSH_A0	".long 0x0275000b"
> +#define THEAD_SYNC_S	".long 0x0190000b"

IIRC this came up before, but these really need to get into the 
assembler as actual instructions.

> +
>  #define ALT_CMO_OP(_op, _start, _size)							\
> -asm volatile(ALTERNATIVE(								\
> +asm volatile(ALTERNATIVE_2(								\
> +	"nop\n\t"									\
>  	"nop\n\t"									\
>  	"nop\n\t"									\
>  	"nop\n\t"									\
> @@ -117,7 +147,16 @@ asm volatile(ALTERNATIVE(								\
>  	CBO_##_op##_A0 "\n\t"								\
>  	"addi a0, a0, %0\n\t"								\
>  	"2:\n\t"									\
> -	"bltu a0, %2, 3b\n\t", 0, CPUFEATURE_CMO, CONFIG_RISCV_DMA_NONCOHERENT)		\
> +	"bltu a0, %2, 3b\n\t"								\
> +	"nop", 0, CPUFEATURE_CMO, CONFIG_RISCV_DMA_NONCOHERENT,				\
> +	"mv a0, %1\n\t"									\
> +	"j 2f\n\t"									\
> +	"3:\n\t"									\
> +	THEAD_##_op##_A0 "\n\t"								\
> +	"addi a0, a0, %0\n\t"								\
> +	"2:\n\t"									\
> +	"bltu a0, %2, 3b\n\t"								\
> +	THEAD_SYNC_S, THEAD_VENDOR_ID, ERRATA_THEAD_CMO, CONFIG_ERRATA_THEAD_CMO)	\
>  	: : "I"(L1_CACHE_BYTES), "r"((_start) & ~(L1_CACHE_BYTES - 1)),			\
>  	    "r"(ALIGN((_start) + (_size), L1_CACHE_BYTES)))