spl: nand: sunxi: introduce the nand_wait_cmd_fifo_empty() helper

One bit in the control registers indicates if the NAND controller is
ready to receive a new command. Otherwise, the command FIFO is full and
we should wait for this bit to flip. It then states that the last
command has been processed and the FIFO is now free to welcome another
command.

Add this sanity check before starting any new command.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>

drivers/mtd/nand/sunxi_nand_spl.c

@@ -155,6 +155,17 @@ static inline int check_value_negated(int offset, int unexpected_bits,
 	return check_value_inner(offset, unexpected_bits, timeout_us, 1);
 }
 
+static int nand_wait_cmd_fifo_empty(void)
+{
+	if (!check_value_negated(SUNXI_NFC_BASE + NFC_ST, NFC_ST_CMD_FIFO_STAT,
+				 DEFAULT_TIMEOUT_US)) {
+		printf("nand: timeout waiting for empty cmd FIFO\n");
+		return -ETIMEDOUT;
+	}
+
+	return 0;
+}
+
 static int nand_wait_int(void)
 {
 	if (!check_value(SUNXI_NFC_BASE + NFC_ST, NFC_ST_CMD_INT_FLAG,
@@ -183,6 +194,8 @@ void nand_init(void)
 	}
 
 	/* reset NAND */
+	nand_wait_cmd_fifo_empty();
+
 	writel(NFC_ST_CMD_INT_FLAG, SUNXI_NFC_BASE + NFC_ST);
 	writel(NFC_SEND_CMD1 | NFC_WAIT_FLAG | NAND_CMD_RESET,
 	       SUNXI_NFC_BASE + NFC_CMD);
@@ -194,6 +207,8 @@ static void nand_apply_config(const struct nfc_config *conf)
 {
 	u32 val;
 
+	nand_wait_cmd_fifo_empty();
+
 	val = readl(SUNXI_NFC_BASE + NFC_CTL);
 	val &= ~NFC_CTL_PAGE_SIZE_MASK;
 	writel(val | NFC_CTL_RAM_METHOD | NFC_CTL_PAGE_SIZE(conf->page_size),
@@ -206,6 +221,8 @@ static int nand_load_page(const struct nfc_config *conf, u32 offs)
 {
 	int page = offs / conf->page_size;
 
+	nand_wait_cmd_fifo_empty();
+
 	writel((NFC_CMD_RNDOUTSTART << NFC_RANDOM_READ_CMD1_OFFSET) |
 	       (NFC_CMD_RNDOUT << NFC_RANDOM_READ_CMD0_OFFSET) |
 	       (NFC_CMD_READSTART << NFC_READ_CMD_OFFSET),
@@ -222,6 +239,8 @@ static int nand_load_page(const struct nfc_config *conf, u32 offs)
 
 static int nand_reset_column(void)
 {
+	nand_wait_cmd_fifo_empty();
+
 	writel((NFC_CMD_RNDOUTSTART << NFC_RANDOM_READ_CMD1_OFFSET) |
 	       (NFC_CMD_RNDOUT << NFC_RANDOM_READ_CMD0_OFFSET) |
 	       (NFC_CMD_RNDOUTSTART << NFC_READ_CMD_OFFSET),