[PATCH v3 3/8] riscv: Avoid TLB flush loops when affected by SiFive CIP-1200

[Samuel Holland <samuel.holland@sifive.com>]

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@sifive.com>
---

Changes in v3:
 - New patch for v3

 arch/riscv/errata/sifive/errata.c | 3 +++
 arch/riscv/include/asm/tlbflush.h | 2 ++
 arch/riscv/mm/tlbflush.c          | 2 +-
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/errata/sifive/errata.c b/arch/riscv/errata/sifive/errata.c
index 3d9a32d791f7..00e011d78866 100644
--- a/arch/riscv/errata/sifive/errata.c
+++ b/arch/riscv/errata/sifive/errata.c
@@ -42,6 +42,9 @@ static bool errata_cip_1200_check_func(unsigned long  arch_id, unsigned long imp
 		return false;
 	if ((impid & 0xffffff) > 0x200630 || impid == 0x1200626)
 		return false;
+
+	tlb_flush_all_threshold = 0;
+
 	return true;
 }
 
diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
index e529a643be17..3b393f765805 100644
--- a/arch/riscv/include/asm/tlbflush.h
+++ b/arch/riscv/include/asm/tlbflush.h
@@ -62,6 +62,8 @@ 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 0feccb8932d2..27b3744b5673 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