ARCv2: SLC: Make sure busy bit is set properly for region ops

c70c4733 "ARCv2: SLC: Make sure busy bit is set properly on SLC flushing"
fixes problem for entire SLC operation where the problem was initially
caught. But given a nature of the issue it is perfectly possible for
busy bit to be read incorrectly even when region operation was started.

So extending initial fix for regional operation as well.
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: stable@vger.kernel.org   #4.10
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/mm/cache.c

@@ -697,6 +697,9 @@ noinline void slc_op(phys_addr_t paddr, unsigned long sz, const int op)
 	write_aux_reg(ARC_REG_SLC_RGN_END, (paddr + sz + l2_line_sz - 1));
 	write_aux_reg(ARC_REG_SLC_RGN_START, paddr);
 
+	/* Make sure "busy" bit reports correct stataus, see STAR 9001165532 */
+	read_aux_reg(ARC_REG_SLC_CTRL);
+
 	while (read_aux_reg(ARC_REG_SLC_CTRL) & SLC_CTRL_BUSY);
 
 	spin_unlock_irqrestore(&lock, flags);