[PATCH] i2c: sh_mobile: request IRQs after mapping registers

[Myeonghun Pak <mhun512@gmail.com>]

The managed IRQ handlers are acquired before the managed register
mapping, so devres unmaps the registers before freeing the IRQs. A
transfer wakes its waiter before the ISR's final register read, and
unregistering the adapter does not synchronize these IRQs. An in-flight
handler can therefore still access the mapping when it is released
during driver detach.

With forced-threaded IRQs, the handler can be preempted after waking the
transfer waiter and before its final ICSR read.

Map the registers before requesting the IRQs so that managed cleanup
frees and synchronizes all handlers before unmapping their registers.
Keep IRQs available while unregistering the adapter because client
removal may perform transfers.

This issue was identified as part of our ongoing research while
reviewing kernel code.

Fixes: 7fe8a9993337 ("i2c: sh_mobile: devm conversion, irq setup")
Co-developed-by: Ijae Kim <ae878000@gmail.com>
Signed-off-by: Ijae Kim <ae878000@gmail.com>
Signed-off-by: Myeonghun Pak <mhun512@gmail.com>

---
Compile-tested with Clang, W=1. No hardware runtime testing.

Based on mainline 0fcb05b72344f40806cbe810de8872f1698bf053.

diff --git a/drivers/i2c/busses/i2c-sh_mobile.c b/drivers/i2c/busses/i2c-sh_mobile.c
index dae8967..3a55f80 100644
--- a/drivers/i2c/busses/i2c-sh_mobile.c
+++ b/drivers/i2c/busses/i2c-sh_mobile.c
@@ -880,10 +880,6 @@ static int sh_mobile_i2c_probe(struct platform_device *dev)
 		return PTR_ERR(pd->clk);
 	}
 
-	ret = sh_mobile_i2c_hook_irqs(dev, pd);
-	if (ret)
-		return ret;
-
 	pd->dev = &dev->dev;
 	platform_set_drvdata(dev, pd);
 
@@ -891,6 +887,10 @@ static int sh_mobile_i2c_probe(struct platform_device *dev)
 	if (IS_ERR(pd->reg))
 		return PTR_ERR(pd->reg);
 
+	ret = sh_mobile_i2c_hook_irqs(dev, pd);
+	if (ret)
+		return ret;
+
 	ret = of_property_read_u32(dev->dev.of_node, "clock-frequency", &bus_speed);
 	pd->bus_speed = (ret || !bus_speed) ? I2C_MAX_STANDARD_MODE_FREQ : bus_speed;
 	pd->clks_per_count = 1;