Re: [PATCH v6 3/4] riscv: Add support for non-coherent devices using zicbom extension

[Guo Ren]

On Wed, Jul 6, 2022 at 6:47 AM Heiko Stuebner <heiko@xxxxxxxxx> wrote:
>
> The Zicbom ISA-extension was ratified in november 2021
> and introduces instructions for dcache invalidate, clean
> and flush operations.
>
> Implement cache management operations for non-coherent devices
> based on them.
>
> Of course not all cores will support this, so implement an
> alternative-based mechanism that replaces empty instructions
> with ones done around Zicbom instructions.
>
> As discussed in previous versions, assume the platform
> being coherent by default so that non-coherent devices need
> to get marked accordingly by firmware.
>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Heiko Stuebner <heiko@xxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Atish Patra <atish.patra@xxxxxxx>
> Cc: Guo Ren <guoren@xxxxxxxxxx>
> Cc: Anup Patel <anup@xxxxxxxxxxxxxx>
> ---
>  arch/riscv/Kconfig                   |  31 ++++++++
>  arch/riscv/Makefile                  |   4 +
>  arch/riscv/include/asm/cache.h       |   4 +
>  arch/riscv/include/asm/cacheflush.h  |  10 +++
>  arch/riscv/include/asm/errata_list.h |  19 ++++-
>  arch/riscv/include/asm/hwcap.h       |   1 +
>  arch/riscv/kernel/cpu.c              |   1 +
>  arch/riscv/kernel/cpufeature.c       |  24 ++++++
>  arch/riscv/kernel/setup.c            |   2 +
>  arch/riscv/mm/Makefile               |   1 +
>  arch/riscv/mm/dma-noncoherent.c      | 112 +++++++++++++++++++++++++++
>  11 files changed, 208 insertions(+), 1 deletion(-)
>  create mode 100644 arch/riscv/mm/dma-noncoherent.c
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 32ffef9f6e5b..f7b2b3a4b7f1 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -113,6 +113,7 @@ config RISCV
>         select MODULES_USE_ELF_RELA if MODULES
>         select MODULE_SECTIONS if MODULES
>         select OF
> +       select OF_DMA_DEFAULT_COHERENT
>         select OF_EARLY_FLATTREE
>         select OF_IRQ
>         select PCI_DOMAINS_GENERIC if PCI
> @@ -218,6 +219,14 @@ config PGTABLE_LEVELS
>  config LOCKDEP_SUPPORT
>         def_bool y
>
> +config RISCV_DMA_NONCOHERENT
> +       bool
> +       select ARCH_HAS_DMA_PREP_COHERENT
> +       select ARCH_HAS_SYNC_DMA_FOR_DEVICE
> +       select ARCH_HAS_SYNC_DMA_FOR_CPU
> +       select ARCH_HAS_SETUP_DMA_OPS
> +       select DMA_DIRECT_REMAP
> +
>  source "arch/riscv/Kconfig.socs"
>  source "arch/riscv/Kconfig.erratas"
>
> @@ -376,6 +385,28 @@ config RISCV_ISA_SVPBMT
>
>            If you don't know what to do here, say Y.
>
> +config CC_HAS_ZICBOM
> +       bool
> +       default y if 64BIT && $(cc-option,-mabi=lp64 -march=rv64ima_zicbom)
> +       default y if 32BIT && $(cc-option,-mabi=lp64 -march=rv32ima_zicbom)
-mabi=lp64 for rv32?
> +
> +config RISCV_ISA_ZICBOM
> +       bool "Zicbom extension support for non-coherent DMA operation"
> +       depends on CC_HAS_ZICBOM
> +       depends on !XIP_KERNEL
> +       select RISCV_DMA_NONCOHERENT
> +       select RISCV_ALTERNATIVE
> +       default y
> +       help
> +          Adds support to dynamically detect the presence of the ZICBOM
> +          extension (Cache Block Management Operations) and enable its
> +          usage.
> +
> +          The Zicbom extension can be used to handle for example
> +          non-coherent DMA support on devices that need it.
> +
> +          If you don't know what to do here, say Y.
> +
>  config FPU
>         bool "FPU support"
>         default y
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 34cf8a598617..fbaabc98b3d2 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -56,6 +56,10 @@ riscv-march-$(CONFIG_RISCV_ISA_C)    := $(riscv-march-y)c
>  toolchain-need-zicsr-zifencei := $(call cc-option-yn, -march=$(riscv-march-y)_zicsr_zifencei)
>  riscv-march-$(toolchain-need-zicsr-zifencei) := $(riscv-march-y)_zicsr_zifencei
>
> +# Check if the toolchain supports Zicbom extension
> +toolchain-supports-zicbom := $(call cc-option-yn, -march=$(riscv-march-y)_zicbom)
> +riscv-march-$(toolchain-supports-zicbom) := $(riscv-march-y)_zicbom
> +
>  KBUILD_CFLAGS += -march=$(subst fd,,$(riscv-march-y))
>  KBUILD_AFLAGS += -march=$(riscv-march-y)
>
> diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h
> index 9b58b104559e..d3036df23ccb 100644
> --- a/arch/riscv/include/asm/cache.h
> +++ b/arch/riscv/include/asm/cache.h
> @@ -11,6 +11,10 @@
>
>  #define L1_CACHE_BYTES         (1 << L1_CACHE_SHIFT)
>
> +#ifdef CONFIG_RISCV_DMA_NONCOHERENT
> +#define ARCH_DMA_MINALIGN L1_CACHE_BYTES
> +#endif
> +
>  /*
>   * RISC-V requires the stack pointer to be 16-byte aligned, so ensure that
>   * the flat loader aligns it accordingly.
> diff --git a/arch/riscv/include/asm/cacheflush.h b/arch/riscv/include/asm/cacheflush.h
> index 23ff70350992..a60acaecfeda 100644
> --- a/arch/riscv/include/asm/cacheflush.h
> +++ b/arch/riscv/include/asm/cacheflush.h
> @@ -42,6 +42,16 @@ void flush_icache_mm(struct mm_struct *mm, bool local);
>
>  #endif /* CONFIG_SMP */
>
> +#ifdef CONFIG_RISCV_ISA_ZICBOM
> +void riscv_init_cbom_blocksize(void);
> +#else
> +static inline void riscv_init_cbom_blocksize(void) { }
> +#endif
> +
> +#ifdef CONFIG_RISCV_DMA_NONCOHERENT
> +void riscv_noncoherent_supported(void);
> +#endif
> +
>  /*
>   * Bits in sys_riscv_flush_icache()'s flags argument.
>   */
> diff --git a/arch/riscv/include/asm/errata_list.h b/arch/riscv/include/asm/errata_list.h
> index 398e351e7002..79d89aeeaa6c 100644
> --- a/arch/riscv/include/asm/errata_list.h
> +++ b/arch/riscv/include/asm/errata_list.h
> @@ -20,7 +20,8 @@
>  #endif
>
>  #define        CPUFEATURE_SVPBMT 0
> -#define        CPUFEATURE_NUMBER 1
> +#define        CPUFEATURE_ZICBOM 1
> +#define        CPUFEATURE_NUMBER 2
>
>  #ifdef __ASSEMBLY__
>
> @@ -87,6 +88,22 @@ asm volatile(ALTERNATIVE(                                            \
>  #define ALT_THEAD_PMA(_val)
>  #endif
>
> +#define ALT_CMO_OP(_op, _start, _size, _cachesize)                     \
> +asm volatile(ALTERNATIVE(                                              \
> +       __nops(5),                                                      \
> +       "mv a0, %1\n\t"                                                 \
> +       "j 2f\n\t"                                                      \
> +       "3:\n\t"                                                        \
> +       "cbo." __stringify(_op) " (a0)\n\t"                             \
> +       "add a0, a0, %0\n\t"                                            \
> +       "2:\n\t"                                                        \
> +       "bltu a0, %2, 3b\n\t", 0,                                       \
> +               CPUFEATURE_ZICBOM, CONFIG_RISCV_ISA_ZICBOM)             \
> +       : : "r"(_cachesize),                                            \
> +           "r"((unsigned long)(_start) & ~((_cachesize) - 1UL)),       \
> +           "r"((unsigned long)(_start) + (_size))                      \
> +       : "a0")
> +
>  #endif /* __ASSEMBLY__ */
>
>  #endif
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index 4e2486881840..6044e402003d 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -53,6 +53,7 @@ extern unsigned long elf_hwcap;
>  enum riscv_isa_ext_id {
>         RISCV_ISA_EXT_SSCOFPMF = RISCV_ISA_EXT_BASE,
>         RISCV_ISA_EXT_SVPBMT,
> +       RISCV_ISA_EXT_ZICBOM,
>         RISCV_ISA_EXT_ID_MAX = RISCV_ISA_EXT_MAX,
>  };
>
> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index fba9e9f46a8c..0365557f7122 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -89,6 +89,7 @@ int riscv_of_parent_hartid(struct device_node *node)
>  static struct riscv_isa_ext_data isa_ext_arr[] = {
>         __RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
>         __RISCV_ISA_EXT_DATA(svpbmt, RISCV_ISA_EXT_SVPBMT),
> +       __RISCV_ISA_EXT_DATA(zicbom, RISCV_ISA_EXT_ZICBOM),
>         __RISCV_ISA_EXT_DATA("", RISCV_ISA_EXT_MAX),
>  };
>
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 6a40cb8134bd..d01a792a7201 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -12,6 +12,7 @@
>  #include <linux/module.h>
>  #include <linux/of.h>
>  #include <asm/alternative.h>
> +#include <asm/cacheflush.h>
>  #include <asm/errata_list.h>
>  #include <asm/hwcap.h>
>  #include <asm/patch.h>
> @@ -199,6 +200,7 @@ void __init riscv_fill_hwcap(void)
>                         } else {
>                                 SET_ISA_EXT_MAP("sscofpmf", RISCV_ISA_EXT_SSCOFPMF);
>                                 SET_ISA_EXT_MAP("svpbmt", RISCV_ISA_EXT_SVPBMT);
> +                               SET_ISA_EXT_MAP("zicbom", RISCV_ISA_EXT_ZICBOM);
>                         }
>  #undef SET_ISA_EXT_MAP
>                 }
> @@ -259,6 +261,25 @@ static bool __init_or_module cpufeature_probe_svpbmt(unsigned int stage)
>         return false;
>  }
>
> +static bool __init_or_module cpufeature_probe_zicbom(unsigned int stage)
> +{
> +#ifdef CONFIG_RISCV_ISA_ZICBOM
> +       switch (stage) {
> +       case RISCV_ALTERNATIVES_EARLY_BOOT:
> +               return false;
> +       default:
> +               if (riscv_isa_extension_available(NULL, ZICBOM)) {
> +                       riscv_noncoherent_supported();
> +                       return true;
> +               } else {
> +                       return false;
> +               }
> +       }
> +#endif
> +
> +       return false;
> +}
> +
>  /*
>   * Probe presence of individual extensions.
>   *
> @@ -273,6 +294,9 @@ static u32 __init_or_module cpufeature_probe(unsigned int stage)
>         if (cpufeature_probe_svpbmt(stage))
>                 cpu_req_feature |= (1U << CPUFEATURE_SVPBMT);
>
> +       if (cpufeature_probe_zicbom(stage))
> +               cpu_req_feature |= (1U << CPUFEATURE_ZICBOM);
> +
>         return cpu_req_feature;
>  }
>
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index f0f36a4a0e9b..95ef6e2bf45c 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -22,6 +22,7 @@
>  #include <linux/crash_dump.h>
>
>  #include <asm/alternative.h>
> +#include <asm/cacheflush.h>
>  #include <asm/cpu_ops.h>
>  #include <asm/early_ioremap.h>
>  #include <asm/pgtable.h>
> @@ -296,6 +297,7 @@ void __init setup_arch(char **cmdline_p)
>  #endif
>
>         riscv_fill_hwcap();
> +       riscv_init_cbom_blocksize();
>         apply_boot_alternatives();
>  }
>
> diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
> index ac7a25298a04..d76aabf4b94d 100644
> --- a/arch/riscv/mm/Makefile
> +++ b/arch/riscv/mm/Makefile
> @@ -30,3 +30,4 @@ endif
>  endif
>
>  obj-$(CONFIG_DEBUG_VIRTUAL) += physaddr.o
> +obj-$(CONFIG_RISCV_DMA_NONCOHERENT) += dma-noncoherent.o
> diff --git a/arch/riscv/mm/dma-noncoherent.c b/arch/riscv/mm/dma-noncoherent.c
> new file mode 100644
> index 000000000000..a8dc0bd9078d
> --- /dev/null
> +++ b/arch/riscv/mm/dma-noncoherent.c
> @@ -0,0 +1,112 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * RISC-V specific functions to support DMA for non-coherent devices
> + *
> + * Copyright (c) 2021 Western Digital Corporation or its affiliates.
> + */
> +
> +#include <linux/dma-direct.h>
> +#include <linux/dma-map-ops.h>
> +#include <linux/mm.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <asm/cacheflush.h>
> +
> +static unsigned int riscv_cbom_block_size = L1_CACHE_BYTES;
> +static bool noncoherent_supported;
> +
> +void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
> +                             enum dma_data_direction dir)
> +{
> +       void *vaddr = phys_to_virt(paddr);
> +
> +       switch (dir) {
> +       case DMA_TO_DEVICE:
> +               ALT_CMO_OP(clean, vaddr, size, riscv_cbom_block_size);
> +               break;
> +       case DMA_FROM_DEVICE:
> +               ALT_CMO_OP(clean, vaddr, size, riscv_cbom_block_size);
> +               break;
> +       case DMA_BIDIRECTIONAL:
> +               ALT_CMO_OP(flush, vaddr, size, riscv_cbom_block_size);
> +               break;
> +       default:
> +               break;
> +       }
> +}
> +
> +void arch_sync_dma_for_cpu(phys_addr_t paddr, size_t size,
> +                          enum dma_data_direction dir)
> +{
> +       void *vaddr = phys_to_virt(paddr);
> +
> +       switch (dir) {
> +       case DMA_TO_DEVICE:
> +               break;
> +       case DMA_FROM_DEVICE:
> +       case DMA_BIDIRECTIONAL:
> +               ALT_CMO_OP(flush, vaddr, size, riscv_cbom_block_size);
> +               break;
> +       default:
> +               break;
> +       }
> +}
> +
> +void arch_dma_prep_coherent(struct page *page, size_t size)
> +{
> +       void *flush_addr = page_address(page);
> +
> +       ALT_CMO_OP(flush, flush_addr, size, riscv_cbom_block_size);
> +}
> +
> +void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
> +               const struct iommu_ops *iommu, bool coherent)
> +{
> +       WARN_TAINT(!coherent && riscv_cbom_block_size > ARCH_DMA_MINALIGN,
> +                  TAINT_CPU_OUT_OF_SPEC,
> +                  "%s %s: ARCH_DMA_MINALIGN smaller than riscv,cbom-block-size (%d < %d)",
> +                  dev_driver_string(dev), dev_name(dev),
> +                  ARCH_DMA_MINALIGN, riscv_cbom_block_size);
> +
> +       WARN_TAINT(!coherent && !noncoherent_supported, TAINT_CPU_OUT_OF_SPEC,
> +                  "%s %s: device non-coherent but no non-coherent operations supported",
> +                  dev_driver_string(dev), dev_name(dev));
> +
> +       dev->dma_coherent = coherent;
> +}
> +
> +#ifdef CONFIG_RISCV_ISA_ZICBOM
> +void riscv_init_cbom_blocksize(void)
> +{
> +       struct device_node *node;
> +       int ret;
> +       u32 val;
> +
> +       for_each_of_cpu_node(node) {
> +               int hartid = riscv_of_processor_hartid(node);
> +               int cbom_hartid;
> +
> +               if (hartid < 0)
> +                       continue;
> +
> +               /* set block-size for cbom extension if available */
> +               ret = of_property_read_u32(node, "riscv,cbom-block-size", &val);
> +               if (ret)
> +                       continue;
> +
> +               if (!riscv_cbom_block_size) {
> +                       riscv_cbom_block_size = val;
> +                       cbom_hartid = hartid;
> +               } else {
> +                       if (riscv_cbom_block_size != val)
> +                               pr_warn("cbom-block-size mismatched between harts %d and %d\n",
> +                                       cbom_hartid, hartid);
> +               }
> +       }
> +}
> +#endif
> +
> +void riscv_noncoherent_supported(void)
> +{
> +       noncoherent_supported = true;
> +}
> --
> 2.35.1
>


-- 
Best Regards
 Guo Ren