[Skiboot] [PATCH] hw/npu2.c: Change MCD BAR allocation order

[Alistair Popple]

MCD BARs need to be correctly aligned to the size of the region. As GPU
memory is allocated from the top of memory down we should start allocating
from the highest GPU memory address to the lowest to ensure correct
alignment.

Signed-off-by: Alistair Popple <alistair at popple.id.au>
---
 hw/npu2.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/hw/npu2.c b/hw/npu2.c
index 8786cc1..0fd6076 100644
--- a/hw/npu2.c
+++ b/hw/npu2.c
@@ -758,17 +758,22 @@ static void npu2_hw_init(struct npu2 *p)
 	 * across both if total_size is not a power of two. */
 	total_size = gpu_max_addr - gpu_min_addr;
 	size = 1ull << ilog2(total_size);
+
+	/* Allocate the biggest chunk first as we assume gpu_max_addr has the
+	 * highest alignment. */
+	addr = gpu_max_addr - size;
 	val = PPC_BIT(0);
 	val = SETFIELD(PPC_BITMASK(13, 29), val, (size >> 25) - 1);
-	val = SETFIELD(PPC_BITMASK(33, 63), val, gpu_min_addr >> 25);
+	val = SETFIELD(PPC_BITMASK(33, 63), val, addr >> 25);
 	xscom_write(p->chip_id, MCD0_BANK0_CN3, val);
 	total_size -= size;
 	if (total_size) {
 	/* total_size was not a power of two, but the remainder should
 	 * be if all GPUs were assigned the same size. */
 		assert(is_pow2(total_size));
-		addr += size;
 		size = 1ull << ilog2(total_size);
+		addr -= size;
+		assert(addr <= gpu_min_addr);
 		val = PPC_BIT(0);
 		val = SETFIELD(PPC_BITMASK(13, 29), val, (size >> 25) - 1);
 		val = SETFIELD(PPC_BITMASK(33, 63), val, addr >> 25);
-- 
2.1.4