board_f: fix noncached reservation calculation

The current code in reserve_noncached() has two issues:

1) The first update of gd->start_addr_sp always rounds down to a section
start. However, the equivalent calculation in cache.c:noncached_init()
always first rounds up to a section start, then subtracts a section size.
These two calculations differ if the initial value is already rounded to
section alignment.

2) The second update of gd->start_addr_sp subtracts exactly
CONFIG_SYS_NONCACHED_MEMORY, whereas the equivalent calculation in
cache.c:noncached_init() rounds the noncached size up to section
alignment before subtracting it. The two calculations differ if the
noncached region size is not a multiple of the MMU section size.

In practice, one/both of those issues causes a practical problem on
Jetson TX1; U-Boot triggers a synchronous abort during initialization,
likely due to overlapping use of some memory region.

This change fixes both these issues by duplicating the exact calculations
from noncached_init() into reserve_noncached().

However, this fix assumes that gd->start_addr_sp on entry to
reserve_noncached() exactly matches mem_malloc_start on entry to
noncached_init(). I haven't traced the code to see whether it absolutely
guarantees this in all (or indeed any!) cases. Consequently, I added some
comments in the hope that this condition will continue to be true.

Fixes: 5f7adb5b1c ("board_f: reserve noncached space below malloc area")
Cc: Vikas Manocha <vikas.manocha@st.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>

arch/arm/lib/cache.c

@@ -77,6 +77,7 @@ void noncached_init(void)
 	phys_addr_t start, end;
 	size_t size;
 
+	/* If this calculation changes, update board_f.c:reserve_noncached() */
 	end = ALIGN(mem_malloc_start, MMU_SECTION_SIZE) - MMU_SECTION_SIZE;
 	size = ALIGN(CONFIG_SYS_NONCACHED_MEMORY, MMU_SECTION_SIZE);
 	start = end - size;

common/board_f.c

@@ -470,9 +470,18 @@ static int reserve_uboot(void)
 #ifdef CONFIG_SYS_NONCACHED_MEMORY
 static int reserve_noncached(void)
 {
-	/* round down to SECTION SIZE (typicaly 1MB) limit */
+	/*
-	gd->start_addr_sp &= ~(MMU_SECTION_SIZE - 1);
+	 * The value of gd->start_addr_sp must match the value of malloc_start
-	gd->start_addr_sp -= CONFIG_SYS_NONCACHED_MEMORY;
+	 * calculated in boatrd_f.c:initr_malloc(), which is passed to
+	 * board_r.c:mem_malloc_init() and then used by
+	 * cache.c:noncached_init()
+	 *
+	 * These calculations must match the code in cache.c:noncached_init()
+	 */
+	gd->start_addr_sp = ALIGN(gd->start_addr_sp, MMU_SECTION_SIZE) -
+		MMU_SECTION_SIZE;
+	gd->start_addr_sp -= ALIGN(CONFIG_SYS_NONCACHED_MEMORY,
+				   MMU_SECTION_SIZE);
 	debug("Reserving %dM for noncached_alloc() at: %08lx\n",
 	      CONFIG_SYS_NONCACHED_MEMORY >> 20, gd->start_addr_sp);
 

common/board_r.c

@@ -247,6 +247,10 @@ static int initr_malloc(void)
 	      gd->malloc_ptr / 1024);
 #endif
 	/* The malloc area is immediately below the monitor copy in DRAM */
+	/*
+	 * This value MUST match the value of gd->start_addr_sp in board_f.c:
+	 * reserve_noncached().
+	 */
 	malloc_start = gd->relocaddr - TOTAL_MALLOC_LEN;
 	mem_malloc_init((ulong)map_sysmem(malloc_start, TOTAL_MALLOC_LEN),
 			TOTAL_MALLOC_LEN);