[PATCH v4 07/12] riscv: Avoid TLB flush loops when affected by SiFive CIP-1200

[Samuel Holland]

Since implementations affected by SiFive errata CIP-1200 always use the
global variant of the sfence.vma instruction, they only need to execute
the instruction once. The range-based loop only hurts performance.

Signed-off-by: Samuel Holland <samuel.holland at sifive.com>
---

Changes in v4:
 - Only set tlb_flush_all_threshold when CONFIG_MMU=y.

Changes in v3:
 - New patch for v3

 arch/riscv/errata/sifive/errata.c | 5 +++++
 arch/riscv/include/asm/tlbflush.h | 2 ++
 arch/riscv/mm/tlbflush.c          | 2 +-
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/errata/sifive/errata.c b/arch/riscv/errata/sifive/errata.c
index 3d9a32d791f7..716cfedad3a2 100644
--- a/arch/riscv/errata/sifive/errata.c
+++ b/arch/riscv/errata/sifive/errata.c
@@ -42,6 +42,11 @@ static bool errata_cip_1200_check_func(unsigned long  arch_id, unsigned long imp
 		return false;
 	if ((impid & 0xffffff) > 0x200630 || impid == 0x1200626)
 		return false;
+
+#ifdef CONFIG_MMU
+	tlb_flush_all_threshold = 0;
+#endif
+
 	return true;
 }
 
diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
index 002c4c2620f3..d9913590f82e 100644
--- a/arch/riscv/include/asm/tlbflush.h
+++ b/arch/riscv/include/asm/tlbflush.h
@@ -58,6 +58,8 @@ void flush_tlb_kernel_range(unsigned long start, unsigned long end);
 void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
 			unsigned long end);
 #endif
+
+extern unsigned long tlb_flush_all_threshold;
 #else /* CONFIG_MMU */
 #define local_flush_tlb_all()			do { } while (0)
 #endif /* CONFIG_MMU */
diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index 292d7cf3c4f6..76b24d4ed4ab 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -11,7 +11,7 @@
  * Flush entire TLB if number of entries to be flushed is greater
  * than the threshold below.
  */
-static unsigned long tlb_flush_all_threshold __read_mostly = 64;
+unsigned long tlb_flush_all_threshold __read_mostly = 64;
 
 static void local_flush_tlb_range_threshold_asid(unsigned long start,
 						 unsigned long size,
-- 
2.42.0