riscv: Add support for non-coherent devices using zicbom extension

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 <[email protected]>
Signed-off-by: Heiko Stuebner <[email protected]>
Reviewed-by: Guo Ren <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: mmind

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=ilp32 -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

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)
 

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.

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.
  */

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__
 
@@ -93,6 +94,22 @@ 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

arch/riscv/include/asm/hwcap.h

@@ -54,6 +54,7 @@ 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,
 };
 

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),
 };
 

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>
@@ -198,6 +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 +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;
 }
 

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();
 }
 

arch/riscv/mm/Makefile

@@ -30,3 +30,4 @@ endif
 endif
 
 obj-$(CONFIG_DEBUG_VIRTUAL) += physaddr.o
+obj-$(CONFIG_RISCV_DMA_NONCOHERENT) += dma-noncoherent.o