[U-Boot] [PATCH RFC 2/2] arm cp15: setup mmu and enable dcache

[Alessandro Rubini]

This has been tested on at91sam9263 and STN8815.
Again, I didn't check if it has bad effects
on non-arm926 cores.

Initially I had a "done" bit to only set up page tables
at the beginning. However, since the aligmnent requirement
was for the whole object file, this extra integer tool 16kB
in BSS, so I chose to remove it.

Also, note not all boards use PHYS_SDRAM, but it looks like
it's the most used name (more than CONFIG_SYS_DRAM_BASE for
example).

Signed-off-by: Alessandro Rubini <rubini at gnudd.com>
---
 lib_arm/cache-cp15.c |   37 +++++++++++++++++++++++++++++++++++++
 1 files changed, 37 insertions(+), 0 deletions(-)

diff --git a/lib_arm/cache-cp15.c b/lib_arm/cache-cp15.c
index 62ed54f..257aea1 100644
--- a/lib_arm/cache-cp15.c
+++ b/lib_arm/cache-cp15.c
@@ -32,6 +32,35 @@ static void cp_delay (void)
 	/* copro seems to need some delay between reading and writing */
 	for (i = 0; i < 100; i++)
 		nop();
+	asm volatile("" : : : "memory");
+}
+
+/* to activate the MMU we need to set up virtual memory: use 1M areas in bss */
+static inline void mmu_setup(void)
+{
+	static u32 __attribute__((aligned(16384))) page_table[4096];
+	int i;
+	u32 reg;
+
+	/* Set up an identity-mapping for all 4GB, rw for everyone */
+	for (i = 0; i < 4096; i++)
+		page_table[i] = i << 20 | (3 << 10) | 0x12;
+	/* Then, enable cacheable and bufferable for RAM only */
+	for (i = PHYS_SDRAM >> 20;
+	     i < ( PHYS_SDRAM + PHYS_SDRAM_SIZE) >> 20;
+	     i++) {
+		page_table[i] = i << 20 | (3 << 10) | 0x1e;
+	}
+	/* Copy the page table address to cp15 */
+	asm volatile("mcr p15, 0, %0, c2, c0, 0"
+		     : : "r" (page_table) : "memory");
+	/* Set the access control to all-supervisor */
+	asm volatile("mcr p15, 0, %0, c3, c0, 0"
+		     : : "r" (~0));
+	/* and enable the mmu */
+	reg = get_cr();	/* get control reg. */
+	cp_delay();
+	set_cr(reg | CR_M);
 }
 
 /* cache_bit must be either CR_I or CR_C */
@@ -39,6 +68,9 @@ static void cache_enable(uint32_t cache_bit)
 {
 	uint32_t reg;
 
+	/* The data cache is not active unless the mmu is enabled too */
+	if (cache_bit == CR_C)
+		mmu_setup();
 	reg = get_cr();	/* get control reg. */
 	cp_delay();
 	set_cr(reg | cache_bit);
@@ -49,6 +81,11 @@ static void cache_disable(uint32_t cache_bit)
 {
 	uint32_t reg;
 
+	if (cache_bit == CR_C) {
+		/* if disabling data cache, disable mmu too */
+		cache_bit |= CR_M;
+		flush_cache(0, ~0);
+	}
 	reg = get_cr();
 	cp_delay();
 	set_cr(reg & ~cache_bit);
-- 
1.6.0.2