[PATCH v5 2/2] mtd: nand: sunxi: add reset line support

The NAND controller on some sun8i chips needs its reset line to be
deasserted before they can enter working state.

Signed-off-by: Icenowy Zheng <redacted>
---
Changes in v2:
  - Corrected the error checking code of reset line.

Changes in v3:
  - Corrected a more serious error brought in the "fix" of v2.

Changes in v4:
  - Removed unneeded code block after "else".

Changes in v5:
  - Added reassertion code in case of initialization error and device
    remove.

 drivers/mtd/nand/sunxi_nand.c | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/nand/sunxi_nand.c b/drivers/mtd/nand/sunxi_nand.c
index a83a690..3b40186 100644
--- a/drivers/mtd/nand/sunxi_nand.c
+++ b/drivers/mtd/nand/sunxi_nand.c

@@ -39,6 +39,7 @@
 #include <linux/gpio.h>
 #include <linux/interrupt.h>
 #include <linux/iopoll.h>
+#include <linux/reset.h>
 
 #define NFC_REG_CTL		0x0000
 #define NFC_REG_ST		0x0004

@@ -269,6 +270,7 @@ struct sunxi_nfc {
 	void __iomem *regs;
 	struct clk *ahb_clk;
 	struct clk *mod_clk;
+	struct reset_control *reset;
 	unsigned long assigned_cs;
 	unsigned long clk_rate;
 	struct list_head chips;

@@ -1871,26 +1873,41 @@ static int sunxi_nfc_probe(struct platform_device *pdev)
 	if (ret)
 		goto out_ahb_clk_unprepare;
 
+	nfc->reset = devm_reset_control_get_optional(dev, "ahb");
+
+	if (!IS_ERR(nfc->reset)) {
+		ret = reset_control_deassert(nfc->reset);
+		if (ret) {
+			dev_err(dev, "reset err %d\n", ret);
+			goto out_mod_clk_unprepare;
+		}
+	} else if (PTR_ERR(nfc->reset) != -ENOENT) {
+		return PTR_ERR(nfc->reset);