mtd: rawnand: marvell: use regmap_update_bits() for syscon access

The marvell_nfc_init() function fiddles with some bits of a system
controller on Armada 7K/8K. However, it does a read/modify/write
sequence on GENCONF_CLK_GATING_CTRL and GENCONF_ND_CLK_CTRL, which
isn't safe from a concurrency point of view, as the regmap lock isn't
taken accross the read/modify/write sequence. To solve this issue, use
regmap_update_bits().

While at it, since the "reg" variable is no longer needed for the
read/modify/write sequences, get rid of it for the regmap_write() to
GENCONF_SOC_DEVICE_MUX, and directly pass the value to be written as
argument.

Fixes: 02f26ecf ("mtd: nand: add reworked Marvell NAND controller driver")
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

drivers/mtd/nand/raw/marvell_nand.c

@@ -2697,24 +2697,23 @@ static int marvell_nfc_init(struct marvell_nfc *nfc)
 		struct regmap *sysctrl_base =
 			syscon_regmap_lookup_by_phandle(np,
 							"marvell,system-controller");
-		u32 reg;
 
 		if (IS_ERR(sysctrl_base))
 			return PTR_ERR(sysctrl_base);
 
-		reg = GENCONF_SOC_DEVICE_MUX_NFC_EN |
+		regmap_write(sysctrl_base, GENCONF_SOC_DEVICE_MUX,
+			     GENCONF_SOC_DEVICE_MUX_NFC_EN |
 			     GENCONF_SOC_DEVICE_MUX_ECC_CLK_RST |
 			     GENCONF_SOC_DEVICE_MUX_ECC_CORE_RST |
-		      GENCONF_SOC_DEVICE_MUX_NFC_INT_EN;
-		regmap_write(sysctrl_base, GENCONF_SOC_DEVICE_MUX, reg);
+			     GENCONF_SOC_DEVICE_MUX_NFC_INT_EN);
 
-		regmap_read(sysctrl_base, GENCONF_CLK_GATING_CTRL, &reg);
-		reg |= GENCONF_CLK_GATING_CTRL_ND_GATE;
-		regmap_write(sysctrl_base, GENCONF_CLK_GATING_CTRL, reg);
+		regmap_update_bits(sysctrl_base, GENCONF_CLK_GATING_CTRL,
+				   GENCONF_CLK_GATING_CTRL_ND_GATE,
+				   GENCONF_CLK_GATING_CTRL_ND_GATE);
 
-		regmap_read(sysctrl_base, GENCONF_ND_CLK_CTRL, &reg);
-		reg |= GENCONF_ND_CLK_CTRL_EN;
-		regmap_write(sysctrl_base, GENCONF_ND_CLK_CTRL, reg);
+		regmap_update_bits(sysctrl_base, GENCONF_ND_CLK_CTRL,
+				   GENCONF_ND_CLK_CTRL_EN,
+				   GENCONF_ND_CLK_CTRL_EN);
 	}
 
 	/* Configure the DMA if appropriate */