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

Jisheng Zhang
2023-09-12T07:39:51Z

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."

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