mfd: rn5t618: Make restart handler atomic safe

The restart handler is executed during the shutdown phase which is
atomic/irq-less. The i2c framework supports atomic transfers since
commit 63b96983a5dd ("i2c: core: introduce callbacks for atomic
transfers") to address this use case. Using i2c regmap in that
situation is not allowed:

[ 165.177465] [ BUG: Invalid wait context ]
[ 165.181479] 5.8.0-rc3-00003-g0e9088558027-dirty #11 Not tainted
[ 165.187400] -----------------------------
[ 165.191410] systemd-shutdow/1 is trying to lock:
[ 165.196030] d85b4438 (rn5t618:170:(&rn5t618_regmap_config)->lock){+.+.}-{3:3}, at: regmap_update_bits_base+0x30/0x70
[ 165.206573] other info that might help us debug this:
[ 165.211625] context-{4:4}
[ 165.214248] 2 locks held by systemd-shutdow/1:
[ 165.218691] #0: c131c47c (system_transition_mutex){+.+.}-{3:3}, at: __do_sys_reboot+0x90/0x204
[ 165.227405] #1: c131efb4 (rcu_read_lock){....}-{1:2}, at: __atomic_notifier_call_chain+0x0/0x118
[ 165.236288] stack backtrace:
[ 165.239174] CPU: 0 PID: 1 Comm: systemd-shutdow Not tainted 5.8.0-rc3-00003-g0e9088558027-dirty #11
[ 165.248220] Hardware name: Freescale i.MX6 SoloLite (Device Tree)
[ 165.254330] [<c0112110>] (unwind_backtrace) from [<c010bfa0>] (show_stack+0x10/0x14)
[ 165.262084] [<c010bfa0>] (show_stack) from [<c058093c>] (dump_stack+0xe8/0x120)
[ 165.269407] [<c058093c>] (dump_stack) from [<c01835a4>] (__lock_acquire+0x81c/0x2ca0)
[ 165.277246] [<c01835a4>] (__lock_acquire) from [<c0186344>] (lock_acquire+0xe4/0x490)
[ 165.285090] [<c0186344>] (lock_acquire) from [<c0c98638>] (__mutex_lock+0x74/0x954)
[ 165.292756] [<c0c98638>] (__mutex_lock) from [<c0c98f34>] (mutex_lock_nested+0x1c/0x24)
[ 165.300769] [<c0c98f34>] (mutex_lock_nested) from [<c07593ec>] (regmap_update_bits_base+0x30/0x70)
[ 165.309741] [<c07593ec>] (regmap_update_bits_base) from [<c076b838>] (rn5t618_trigger_poweroff_sequence+0x34/0x64)
[ 165.320097] [<c076b838>] (rn5t618_trigger_poweroff_sequence) from [<c076b874>] (rn5t618_restart+0xc/0x2c)
[ 165.329669] [<c076b874>] (rn5t618_restart) from [<c01514f8>] (notifier_call_chain+0x48/0x80)
[ 165.338113] [<c01514f8>] (notifier_call_chain) from [<c01516a8>] (__atomic_notifier_call_chain+0x70/0x118)
[ 165.347770] [<c01516a8>] (__atomic_notifier_call_chain) from [<c0151768>] (atomic_notifier_call_chain+0x18/0x20)
[ 165.357949] [<c0151768>] (atomic_notifier_call_chain) from [<c010a828>] (machine_restart+0x68/0x80)
[ 165.367001] [<c010a828>] (machine_restart) from [<c0153224>] (__do_sys_reboot+0x11c/0x204)
[ 165.375272] [<c0153224>] (__do_sys_reboot) from [<c0100080>] (ret_fast_syscall+0x0/0x28)
[ 165.383364] Exception stack(0xd80a5fa8 to 0xd80a5ff0)
[ 165.388420] 5fa0: 00406948 00000000 fee1dead 28121969 01234567 73299b00
[ 165.396602] 5fc0: 00406948 00000000 00000000 00000058 be91abc8 00000000 be91ab60 004056f8
[ 165.404781] 5fe0: 00000058 be91aabc b6ed4d45 b6e56746

Signed-off-by: Andreas Kemnade <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/rn5t618.c

···
 	.mask_invert = true,
 };
 
-static struct rn5t618 *rn5t618_pm_power_off;
+static struct i2c_client *rn5t618_pm_power_off;
 static struct notifier_block rn5t618_restart_handler;
 
 static int rn5t618_irq_init(struct rn5t618 *rn5t618)
···
 
 static void rn5t618_trigger_poweroff_sequence(bool repower)
 {
+	int ret;
+
 	/* disable automatic repower-on */
-	regmap_update_bits(rn5t618_pm_power_off->regmap, RN5T618_REPCNT,
-			   RN5T618_REPCNT_REPWRON,
-			   repower ? RN5T618_REPCNT_REPWRON : 0);
+	ret = i2c_smbus_read_byte_data(rn5t618_pm_power_off, RN5T618_REPCNT);
+	if (ret < 0)
+		goto err;
+
+	ret &= ~RN5T618_REPCNT_REPWRON;
+	if (repower)
+		ret |= RN5T618_REPCNT_REPWRON;
+
+	ret = i2c_smbus_write_byte_data(rn5t618_pm_power_off,
+					RN5T618_REPCNT, (u8)ret);
+	if (ret < 0)
+		goto err;
+
 	/* start power-off sequence */
-	regmap_update_bits(rn5t618_pm_power_off->regmap, RN5T618_SLPCNT,
-			   RN5T618_SLPCNT_SWPWROFF, RN5T618_SLPCNT_SWPWROFF);
+	ret = i2c_smbus_read_byte_data(rn5t618_pm_power_off, RN5T618_SLPCNT);
+	if (ret < 0)
+		goto err;
+
+	ret |= RN5T618_SLPCNT_SWPWROFF;
+
+	ret = i2c_smbus_write_byte_data(rn5t618_pm_power_off,
+					RN5T618_SLPCNT, (u8)ret);
+	if (ret < 0)
+		goto err;
+
+	return;
+
+err:
+	dev_alert(&rn5t618_pm_power_off->dev, "Failed to shutdown (err = %d)\n", ret);
 }
 
 static void rn5t618_power_off(void)
···
 		return ret;
 	}
 
-	rn5t618_pm_power_off = priv;
+	rn5t618_pm_power_off = i2c;
 	if (of_device_is_system_power_controller(i2c->dev.of_node)) {
 		if (!pm_power_off)
 			pm_power_off = rn5t618_power_off;
···
 
 static int rn5t618_i2c_remove(struct i2c_client *i2c)
 {
-	struct rn5t618 *priv = i2c_get_clientdata(i2c);
-
-	if (priv == rn5t618_pm_power_off) {
+	if (i2c == rn5t618_pm_power_off) {
 		rn5t618_pm_power_off = NULL;
 		pm_power_off = NULL;
 	}