mtd: nand: brcmnand: Check flash #WP pin status before nand erase/program

On brcmnand controller v6.x and v7.x, the #WP pin is controlled through
the NAND_WP bit in CS_SELECT register.

The driver currently assumes that toggling the #WP pin is
instantaneously enabling/disabling write-protection, but it actually
takes some time to propagate the new state to the internal NAND chip
logic. This behavior is sometime causing data corruptions when an
erase/program operation is executed before write-protection has really
been disabled.

Fixes: 27c5b17cd1b1 ("mtd: nand: add NAND driver "library" for Broadcom STB NAND controller")
Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

drivers/mtd/nand/brcmnand/brcmnand.c

@@ -101,6 +101,9 @@ struct brcm_nand_dma_desc {
 #define BRCMNAND_MIN_BLOCKSIZE	(8 * 1024)
 #define BRCMNAND_MIN_DEVSIZE	(4ULL * 1024 * 1024)
 
+#define NAND_CTRL_RDY			(INTFC_CTLR_READY | INTFC_FLASH_READY)
+#define NAND_POLL_STATUS_TIMEOUT_MS	100
+
 /* Controller feature flags */
 enum {
 	BRCMNAND_HAS_1K_SECTORS			= BIT(0),
@@ -765,6 +768,31 @@ enum {
 	CS_SELECT_AUTO_DEVICE_ID_CFG		= BIT(30),
 };
 
+static int bcmnand_ctrl_poll_status(struct brcmnand_controller *ctrl,
+				    u32 mask, u32 expected_val,
+				    unsigned long timeout_ms)
+{
+	unsigned long limit;
+	u32 val;
+
+	if (!timeout_ms)
+		timeout_ms = NAND_POLL_STATUS_TIMEOUT_MS;
+
+	limit = jiffies + msecs_to_jiffies(timeout_ms);
+	do {
+		val = brcmnand_read_reg(ctrl, BRCMNAND_INTFC_STATUS);
+		if ((val & mask) == expected_val)
+			return 0;
+
+		cpu_relax();
+	} while (time_after(limit, jiffies));
+
+	dev_warn(ctrl->dev, "timeout on status poll (expected %x got %x)\n",
+		 expected_val, val & mask);
+
+	return -ETIMEDOUT;
+}
+
 static inline void brcmnand_set_wp(struct brcmnand_controller *ctrl, bool en)
 {
 	u32 val = en ? CS_SELECT_NAND_WP : 0;
@@ -1024,12 +1052,39 @@ static void brcmnand_wp(struct mtd_info *mtd, int wp)
 
 	if ((ctrl->features & BRCMNAND_HAS_WP) && wp_on == 1) {
 		static int old_wp = -1;
+		int ret;
 
 		if (old_wp != wp) {
 			dev_dbg(ctrl->dev, "WP %s\n", wp ? "on" : "off");
 			old_wp = wp;
 		}
+
+		/*
+		 * make sure ctrl/flash ready before and after
+		 * changing state of #WP pin
+		 */
+		ret = bcmnand_ctrl_poll_status(ctrl, NAND_CTRL_RDY |
+					       NAND_STATUS_READY,
+					       NAND_CTRL_RDY |
+					       NAND_STATUS_READY, 0);
+		if (ret)
+			return;
+
 		brcmnand_set_wp(ctrl, wp);
+		chip->cmdfunc(mtd, NAND_CMD_STATUS, -1, -1);
+		/* NAND_STATUS_WP 0x00 = protected, 0x80 = not protected */
+		ret = bcmnand_ctrl_poll_status(ctrl,
+					       NAND_CTRL_RDY |
+					       NAND_STATUS_READY |
+					       NAND_STATUS_WP,
+					       NAND_CTRL_RDY |
+					       NAND_STATUS_READY |
+					       (wp ? 0 : NAND_STATUS_WP), 0);
+
+		if (ret)
+			dev_err_ratelimited(&host->pdev->dev,
+					    "nand #WP expected %s\n",
+					    wp ? "on" : "off");
 	}
 }
 
@@ -1157,15 +1212,15 @@ static irqreturn_t brcmnand_dma_irq(int irq, void *data)
 static void brcmnand_send_cmd(struct brcmnand_host *host, int cmd)
 {
 	struct brcmnand_controller *ctrl = host->ctrl;
-	u32 intfc;
+	int ret;
 
 	dev_dbg(ctrl->dev, "send native cmd %d addr_lo 0x%x\n", cmd,
 		brcmnand_read_reg(ctrl, BRCMNAND_CMD_ADDRESS));
 	BUG_ON(ctrl->cmd_pending != 0);
 	ctrl->cmd_pending = cmd;
 
-	intfc = brcmnand_read_reg(ctrl, BRCMNAND_INTFC_STATUS);
-	WARN_ON(!(intfc & INTFC_CTLR_READY));
+	ret = bcmnand_ctrl_poll_status(ctrl, NAND_CTRL_RDY, NAND_CTRL_RDY, 0);
+	WARN_ON(ret);
 
 	mb(); /* flush previous writes */
 	brcmnand_write_reg(ctrl, BRCMNAND_CMD_START,