Re: [PATCH] riscv: errata: thead: use riscv_nonstd_cache_ops for CMO

Emil Renner Berthing
2023-09-29T22:13:07Z

Jisheng Zhang wrote:
> Previously, we use alternative mechanism to dynamically patch
> the CMO operations for THEAD C906/C910 during boot for performance
> reason. But as pointed out by Arnd, "there is already a significant
> cost in accessing the invalidated cache lines afterwards, which is
> likely going to be much higher than the cost of an indirect branch".
> And indeed, there's no performance difference with GMAC and EMMC per
> my test on Sipeed Lichee Pi 4A board.
>
> Use riscv_nonstd_cache_ops for THEAD C906/C910 CMO to simplify
> the alternative code, and to acchieve Arnd's goal -- "I think
> moving the THEAD ops at the same level as all nonstandard operations
> makes sense, but I'd still leave CMO as an explicit fast path that
> avoids the indirect branch. This seems like the right thing to do both
> for readability and for platforms on which the indirect branch has a
> noticeable overhead."

Hi Jisheng,

Thank you for doing this! This boots fine on my Nezha board (Allwinner D1)
running btrfs on the sd-card which was quick to find bugs when this code
first went upstream.

Tested-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>

> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> ---
> arch/riscv/Kconfig.errata | 1 +
> arch/riscv/errata/thead/errata.c | 76 +++++++++++++++++++++++++++-
> arch/riscv/include/asm/errata_list.h | 50 +++---------------
> 3 files changed, 81 insertions(+), 46 deletions(-)
>
> diff --git a/arch/riscv/Kconfig.errata b/arch/riscv/Kconfig.errata
> index 566bcefeab50..d7972914f9de 100644
> --- a/arch/riscv/Kconfig.errata
> +++ b/arch/riscv/Kconfig.errata
> @@ -78,6 +78,7 @@ config ERRATA_THEAD_CMO
> bool "Apply T-Head cache management errata"
> depends on ERRATA_THEAD && MMU
> select RISCV_DMA_NONCOHERENT
> + select RISCV_NONSTANDARD_CACHE_OPS
> default y
> help
> This will apply the cache management errata to handle the
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index 0554ed4bf087..1c320abfe446 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -12,8 +12,10 @@
> #include <asm/alternative.h>
> #include <asm/cacheflush.h>
> #include <asm/cpufeature.h>
> +#include <asm/dma-noncoherent.h>
> #include <asm/errata_list.h>
> #include <asm/hwprobe.h>
> +#include <asm/io.h>
> #include <asm/patch.h>
> #include <asm/vendorid_list.h>
>
> @@ -33,6 +35,75 @@ static bool errata_probe_pbmt(unsigned int stage,
> return false;
> }
>
> +/*
> + * 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 00101 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 0x0255000b"
> +#define THEAD_flush_A0 ".long 0x0275000b"
> +#define THEAD_SYNC_S ".long 0x0190000b"
> +
> +#define THEAD_CMO_OP(_op, _start, _size, _cachesize) \
> +asm volatile("mv a0, %1\n\t" \
> + "j 2f\n\t" \
> + "3:\n\t" \
> + THEAD_##_op##_A0 "\n\t" \
> + "add a0, a0, %0\n\t" \
> + "2:\n\t" \
> + "bltu a0, %2, 3b\n\t" \
> + THEAD_SYNC_S \
> + : : "r"(_cachesize), \
> + "r"((unsigned long)(_start) & ~((_cachesize) - 1UL)), \
> + "r"((unsigned long)(_start) + (_size)) \
> + : "a0")
> +
> +static void thead_errata_cache_inv(phys_addr_t paddr, size_t size)
> +{
> + void *vaddr = phys_to_virt(paddr);
> +
> + THEAD_CMO_OP(inval, vaddr, size, riscv_cbom_block_size);
> +}
> +
> +static void thead_errata_cache_wback(phys_addr_t paddr, size_t size)
> +{
> + void *vaddr = phys_to_virt(paddr);
> +
> + THEAD_CMO_OP(clean, vaddr, size, riscv_cbom_block_size);
> +}
> +
> +static void thead_errata_cache_wback_inv(phys_addr_t paddr, size_t size)
> +{
> + void *vaddr = phys_to_virt(paddr);
> +
> + THEAD_CMO_OP(flush, vaddr, size, riscv_cbom_block_size);
> +}
> +
> +static const struct riscv_nonstd_cache_ops thead_errata_cmo_ops = {
> + .wback = &thead_errata_cache_wback,
> + .inv = &thead_errata_cache_inv,
> + .wback_inv = &thead_errata_cache_wback_inv,
> +};
> +
> static bool errata_probe_cmo(unsigned int stage,
> unsigned long arch_id, unsigned long impid)
> {
> @@ -48,6 +119,8 @@ static bool errata_probe_cmo(unsigned int stage,
> if (stage == RISCV_ALTERNATIVES_BOOT) {
> riscv_cbom_block_size = L1_CACHE_BYTES;
> riscv_noncoherent_supported();
> + if (IS_ENABLED(CONFIG_RISCV_NONSTANDARD_CACHE_OPS))
> + riscv_noncoherent_register_cache_ops(&thead_errata_cmo_ops);
> }
>
> return true;
> @@ -77,8 +150,7 @@ static u32 thead_errata_probe(unsigned int stage,
> if (errata_probe_pbmt(stage, archid, impid))
> cpu_req_errata |= BIT(ERRATA_THEAD_PBMT);
>
> - if (errata_probe_cmo(stage, archid, impid))
> - cpu_req_errata |= BIT(ERRATA_THEAD_CMO);
> + errata_probe_cmo(stage, archid, impid);
>
> if (errata_probe_pmu(stage, archid, impid))
> cpu_req_errata |= BIT(ERRATA_THEAD_PMU);
> diff --git a/arch/riscv/include/asm/errata_list.h b/arch/riscv/include/asm/errata_list.h
> index b55b434f0059..ea33288f8a25 100644
> --- a/arch/riscv/include/asm/errata_list.h
> +++ b/arch/riscv/include/asm/errata_list.h
> @@ -24,9 +24,8 @@
>
> #ifdef CONFIG_ERRATA_THEAD
> #define ERRATA_THEAD_PBMT 0
> -#define ERRATA_THEAD_CMO 1
> -#define ERRATA_THEAD_PMU 2
> -#define ERRATA_THEAD_NUMBER 3
> +#define ERRATA_THEAD_PMU 1
> +#define ERRATA_THEAD_NUMBER 2
> #endif
>
> #ifdef __ASSEMBLY__
> @@ -94,54 +93,17 @@ asm volatile(ALTERNATIVE( \
> #define ALT_THEAD_PMA(_val)
> #endif
>
> -/*
> - * 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 00101 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 0x0255000b"
> -#define THEAD_flush_A0 ".long 0x0275000b"
> -#define THEAD_SYNC_S ".long 0x0190000b"
> -
> #define ALT_CMO_OP(_op, _start, _size, _cachesize) \
> -asm volatile(ALTERNATIVE_2( \
> - __nops(6), \
> +asm volatile(ALTERNATIVE( \
> + __nops(5), \
> "mv a0, %1\n\t" \
> "j 2f\n\t" \
> "3:\n\t" \
> CBO_##_op(a0) \
> "add a0, a0, %0\n\t" \
> "2:\n\t" \
> - "bltu a0, %2, 3b\n\t" \
> - "nop", 0, RISCV_ISA_EXT_ZICBOM, CONFIG_RISCV_ISA_ZICBOM, \
> - "mv a0, %1\n\t" \
> - "j 2f\n\t" \
> - "3:\n\t" \
> - THEAD_##_op##_A0 "\n\t" \
> - "add 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) \
> + "bltu a0, %2, 3b\n\t", \
> + 0, RISCV_ISA_EXT_ZICBOM, CONFIG_RISCV_ISA_ZICBOM) \
> : : "r"(_cachesize), \
> "r"((unsigned long)(_start) & ~((_cachesize) - 1UL)), \
> "r"((unsigned long)(_start) + (_size)) \
> --
> 2.40.1
>
>
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