ARCv2: IOC: Adhere to progamming model guidelines to avoid DMA corruption

On AXS103 release bitfiles, DMA data corruptions were seen because IOC
setup was not following the recommended way in documentation.

Flipping IOC on when caches are enabled or coherency transactions are in
flight, might cause some of the memory operations to not observe
coherency as expected.

So strictly follow the programming model recommendations as documented
in comment header above arc_ioc_setup()

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

1 files changed, 46 insertions, 0 deletions

diff --git a/arch/arc/mm/cache.c b/arch/arc/mm/cache.c
index 2c36370a1689..1b4cda10844a 100644
--- a/arch/arc/mm/cache.c
+++ b/arch/arc/mm/cache.c
@@ -462,6 +462,21 @@ static inline void __dc_entire_op(const int op)
 	__after_dc_op(op);
 }
 
+static inline void __dc_disable(void)
+{
+	const int r = ARC_REG_DC_CTRL;
+
+	__dc_entire_op(OP_FLUSH_N_INV);
+	write_aux_reg(r, read_aux_reg(r) | DC_CTRL_DIS);
+}
+
+static void __dc_enable(void)
+{
+	const int r = ARC_REG_DC_CTRL;
+
+	write_aux_reg(r, read_aux_reg(r) & ~DC_CTRL_DIS);
+}
+
 /* For kernel mappings cache operation: index is same as paddr */
 #define __dc_line_op_k(p, sz, op)	__dc_line_op(p, p, sz, op)
 
@@ -487,6 +502,8 @@ static inline void __dc_line_op(phys_addr_t paddr, unsigned long vaddr,
 #else
 
 #define __dc_entire_op(op)
+#define __dc_disable()
+#define __dc_enable()
 #define __dc_line_op(paddr, vaddr, sz, op)
 #define __dc_line_op_k(paddr, sz, op)
 
@@ -961,12 +978,41 @@ SYSCALL_DEFINE3(cacheflush, uint32_t, start, uint32_t, sz, uint32_t, flags)
 	return 0;
 }
 
+/*
+ * IO-Coherency (IOC) setup rules:
+ *
+ * 1. Needs to be at system level, so only once by Master core
+ *    Non-Masters need not be accessing caches at that time
+ *    - They are either HALT_ON_RESET and kick started much later or
+ *    - if run on reset, need to ensure that arc_platform_smp_wait_to_boot()
+ *      doesn't perturb caches or coherency unit
+ *
+ * 2. caches (L1 and SLC) need to be purged (flush+inv) before setting up IOC,
+ *    otherwise any straggler data might behave strangely post IOC enabling
+ *
+ * 3. All Caches need to be disabled when setting up IOC to elide any in-flight
+ *    Coherency transactions
+ */
 noinline void arc_ioc_setup(void)
 {
+	/* Flush + invalidate + disable L1 dcache */
+	__dc_disable();
+
+	/* Flush + invalidate SLC */
+	if (read_aux_reg(ARC_REG_SLC_BCR))
+		slc_entire_op(OP_FLUSH_N_INV);
+
+	/* IOC Aperture start: TDB: handle non default CONFIG_LINUX_LINK_BASE */
 	write_aux_reg(ARC_REG_IO_COH_AP0_BASE, 0x80000);
+
+	/* IOC Aperture size: TBD: handle different mem sizes, PAE... */
 	write_aux_reg(ARC_REG_IO_COH_AP0_SIZE, 0x11);
+
 	write_aux_reg(ARC_REG_IO_COH_PARTIAL, 1);
 	write_aux_reg(ARC_REG_IO_COH_ENABLE, 1);
+
+	/* Re-enable L1 dcache */
+	__dc_enable();
 }
 
 void arc_cache_init(void)