MIPS: c-r4k: Invalidate BMIPS5000 ZSCM prefetch lines

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 <[e-mail]>
Reviewed-by: Florian Fainelli <[e-mail]>
Signed-off-by: Thomas Bogendoerfer <[e-mail]>

arch/mips/mm/c-r4k.c

···
 	__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 */
···
 		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)