soc: aspeed: xdma: Reduce AST2600 max transfer size (torvalds#254)

There have observations of incomplete DMA transfers under certain
transfer size and host address alignment conditions. Specically,
if the transfer size is within one "page" size of the max transfer
size, and (host address - host address lower page boundary) >=
(max transfer size - transfer size). Page refers to the XDMA PCIe
downstream request size. Therefore, reduce the max transfer size to
below the range where this issue seems to occur.

Signed-off-by: Eddie James <[email protected]>
Co-authored-by: Eddie James <[email protected]>

Author: 2 people

drivers/soc/aspeed/aspeed-xdma.c

@@ -164,6 +164,8 @@
 #define XDMA_AST2600_INPRG_US_CMD20		0x70
 #define XDMA_AST2600_INPRG_US_CMD21		0x74
 
+#define XDMA_AST2600_MAX_LEN		(XDMA_CMD_AST2600_CMD_LINE_SIZE - 255)
+
 struct aspeed_xdma_cmd {
 	u64 host_addr;
 	u64 pitch;
@@ -378,7 +380,7 @@ static unsigned int aspeed_xdma_ast2600_set_cmd(struct aspeed_xdma *ctx,
 		"host[%016llx]\n", op->direction ? "upstream" : "downstream",
 		bmc_addr, op->len, op->host_addr);
 
-	if (op->len > XDMA_CMD_AST2600_CMD_LINE_SIZE) {
+	if (op->len > XDMA_AST2600_MAX_LEN) {
 		unsigned int rem;
 		unsigned int total;