diff mbox series

[3/4] riscv: Implement Zicbom-based cache management operations

Message ID 20220619203212.3604485-4-heiko@sntech.de (mailing list archive)
State New, archived
Headers show
Series riscv: implement Zicbom-based CMO instructions + the t-head variant | expand

Commit Message

Heiko Stuebner June 19, 2022, 8:32 p.m. UTC 
The Zicbom ISA-extension was ratified in november 2021
and introduces instructions for dcache invalidate, clean
and flush operations.

Implement cache management operations 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.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Atish Patra <atish.patra@wdc.com>
Cc: Guo Ren <guoren@kernel.org>
Cc: Anup Patel <anup@brainfault.org>
---
 arch/riscv/Kconfig                   | 31 +++++++++
 arch/riscv/Makefile                  |  4 ++
 arch/riscv/include/asm/cache.h       |  4 ++
 arch/riscv/include/asm/cacheflush.h  |  6 ++
 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       | 18 ++++++
 arch/riscv/kernel/setup.c            |  2 +
 arch/riscv/mm/Makefile               |  1 +
 arch/riscv/mm/dma-noncoherent.c      | 96 ++++++++++++++++++++++++++++
 11 files changed, 182 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/mm/dma-noncoherent.c

Comments

Christoph Hellwig June 20, 2022, 6:16 a.m. UTC | #1 
On Sun, Jun 19, 2022 at 10:32:11PM +0200, Heiko Stuebner wrote:
> +#ifdef CONFIG_RISCV_DMA_NONCOHERENT
> +#define ARCH_DMA_MINALIGN L1_CACHE_BYTES
> +#endif

This needs to be greater or equal to riscv_cbom_block_size, but the
core code requires a compile time constant here.  So we'll need a big
fat comment here, and panic if riscv_cbom_block_size is >
L1_CACHE_BYTES/ARCH_DMA_MINALIGN in the code that queries
riscv_cbom_block_size.

Note that the arm64 folks are looking into making this variable or
killing it off in this current form, so things might be getting better
soon.

> +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(inval, vaddr, size, riscv_cbom_block_size);
> +		break;

For this also see:

https://lore.kernel.org/all/20220606152150.GA31568@willie-the-truck/

and

https://lore.kernel.org/linux-arm-kernel/20220610151228.4562-1-will@kernel.org/T/

> +void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
> +		const struct iommu_ops *iommu, bool coherent)
> +{
> +	dev->dma_coherent = coherent;
> +}

This probably wants a sanity check warn if coherent if false without
any support for cache flushing as that will cause data corruption.
Heiko Stuebner June 24, 2022, 7:49 a.m. UTC | #2 
Hi Christoph,

Am Montag, 20. Juni 2022, 08:16:07 CEST schrieb Christoph Hellwig:
> On Sun, Jun 19, 2022 at 10:32:11PM +0200, Heiko Stuebner wrote:
> > +#ifdef CONFIG_RISCV_DMA_NONCOHERENT
> > +#define ARCH_DMA_MINALIGN L1_CACHE_BYTES
> > +#endif
> 
> This needs to be greater or equal to riscv_cbom_block_size, but the
> core code requires a compile time constant here.  So we'll need a big
> fat comment here, and panic if riscv_cbom_block_size is >
> L1_CACHE_BYTES/ARCH_DMA_MINALIGN in the code that queries
> riscv_cbom_block_size.

ARM people also had this nice WARN_TAINT to warn when the similar
case happens on ARM64 and the ARCH_DMA_MINALIGN is smaller than
the register value so I've added a similar mechanism.

I've read numerous mails from Torvalds over time that panic-ing should
only ever be the very very last resort, so that WARN_TAINT looks like
a less drastic option while still generating that big warning to users.


> Note that the arm64 folks are looking into making this variable or
> killing it off in this current form, so things might be getting better
> soon.
> 
> > +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(inval, vaddr, size, riscv_cbom_block_size);
> > +		break;
> 
> For this also see:
> 
> https://lore.kernel.org/all/20220606152150.GA31568@willie-the-truck/
> 
> and
> 
> https://lore.kernel.org/linux-arm-kernel/20220610151228.4562-1-will@kernel.org/T/

so from that discussion, it looks like a "clean" should happen here to
prevent stale bytes (not written to by the dma transfer itself) in the
buffer area I guess.

I'll give that a spin :-)

> > +void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
> > +		const struct iommu_ops *iommu, bool coherent)
> > +{
> > +	dev->dma_coherent = coherent;
> > +}
> 
> This probably wants a sanity check warn if coherent if false without
> any support for cache flushing as that will cause data corruption.

I've added a riscv_noncoherent_supported() call that will track that
"somebody" implemented non-coherence functionality from their
setup function (zicbom_probe, thead_errata-probe) and a matching
second WARN_TAINT in arch_setup_dma_ops() when coherent value
and availability of non-coherence handling is not matched.

Heiko
diff mbox series

Patch

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 && $(cc-option,-mabi=lp64 -march=rv32ima_zicbom)
+
+config RISCV_ISA_ZICBOM
+	bool "Zicbom extension support for non-coherent DMA operation"
+	depends on CC_HAS_ZICBOM
+	depends on !XIP_KERNEL
+	select RISCV_DMA_NONCOHERENT
+	select RISCV_ALTERNATIVE
+	default y
+	help
+	   Adds support to dynamically detect the presence of the ZICBOM
+	   extension (Cache Block Management Operations) and enable its
+	   usage.
+
+	   The Zicbom extension can be used to handle for example
+	   non-coherent DMA support on devices that need it.
+
+	   If you don't know what to do here, say Y.
+
 config FPU
 	bool "FPU support"
 	default y
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 34cf8a598617..fbaabc98b3d2 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -56,6 +56,10 @@  riscv-march-$(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..eb12d014b158 100644
--- a/arch/riscv/include/asm/cacheflush.h
+++ b/arch/riscv/include/asm/cacheflush.h
@@ -42,6 +42,12 @@  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
+
 /*
  * 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..c66bf5c33cc3 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -199,6 +199,7 @@  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 +260,20 @@  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:
+		return riscv_isa_extension_available(NULL, ZICBOM);
+	}
+#endif
+
+	return false;
+}
+
 /*
  * Probe presence of individual extensions.
  *
@@ -273,6 +288,9 @@  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..6be6ff2cd5d8
--- /dev/null
+++ b/arch/riscv/mm/dma-noncoherent.c
@@ -0,0 +1,96 @@ 
+// 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;
+
+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(inval, 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)
+{
+	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