[PATCH v2] MIPS: c-r4k: Invalidate BMIPS5000 ZSCM prefetch lines

[Kamal Dasu]

Zephyr secondary cache is 256KB, 128B lines. 32B sectors. A secondary cache
line can contain two instruction cache lines (64B), or four data cache
lines (32B). Hardware prefetch Cache detects stream access, and prefetches
ahead of processor access. Add support to invalidate BMIPS5000 cpu zephyr
secondary cache module (ZSCM) on DMA from device so that data returned is
coherent during DMA read operations.

Signed-off-by: Kamal Dasu <kdasu.kdev@xxxxxxxxx>
---
 arch/mips/mm/c-r4k.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/arch/mips/mm/c-r4k.c b/arch/mips/mm/c-r4k.c
index 5f3d0103b95d..acd9ef383e97 100644
--- a/arch/mips/mm/c-r4k.c
+++ b/arch/mips/mm/c-r4k.c
@@ -901,6 +901,31 @@ static void r4k_dma_cache_wback_inv(unsigned long addr, unsigned long size)
 	__sync();
 }
 
+static void prefetch_cache_inv(unsigned long addr, unsigned long size)
+{
+	unsigned int linesz = cpu_scache_line_size();
+	unsigned long addr0 = addr, addr1;
+
+	addr0 &= ~(linesz - 1);
+	addr1 = (addr0 + size - 1) & ~(linesz - 1);
+
+	protected_writeback_scache_line(addr0);
+	if (likely(addr1 != addr0))
+		protected_writeback_scache_line(addr1);
+	else
+		return;
+
+	addr0 += linesz;
+	if (likely(addr1 != addr0))
+		protected_writeback_scache_line(addr0);
+	else
+		return;
+
+	addr1 -= linesz;
+	if (likely(addr1 > addr0))
+		protected_writeback_scache_line(addr0);
+}
+
 static void r4k_dma_cache_inv(unsigned long addr, unsigned long size)
 {
 	/* Catch bad driver code */
@@ -908,6 +933,10 @@ static void r4k_dma_cache_inv(unsigned long addr, unsigned long size)
 		return;
 
 	preempt_disable();
+
+	if (current_cpu_type() == CPU_BMIPS5000)
+		prefetch_cache_inv(addr, size);
+
 	if (cpu_has_inclusive_pcaches) {
 		if (size >= scache_size) {
 			if (current_cpu_type() != CPU_LOONGSON64)
-- 
2.17.1