[PATCH 5.10.y] serial: sc16is7xx: declare MCR and IER as volatile registers

[Sasha Levin <sashal@kernel.org>]

From: Hugo Villeneuve <hvilleneuve@dimonoff.com>

[ Upstream commit 1c41d09dcd07ee9648e20aa8238e404c2e6a12fb ]

MCR register has the same address as XON1 register.
IER register has the same address as DLH register.

Which register is accessed depends on bits configuration in some
other registers.

To prevent potential access errors, declare MCR and IER as volatile
registers.

Fixes: dfeae619d781 ("serial: sc16is7xx")
Cc: stable@kernel.org
Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://patch.msgid.link/20261006192540.234402-1-hugo@hugovil.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ sashal: adjusted context to match the existing switch using reg >> SC16IS7XX_REG_SHIFT ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/serial/sc16is7xx.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index e177df2c4ea22..1934fce0fa732 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -467,7 +467,9 @@ static bool sc16is7xx_regmap_volatile(struct device *dev, unsigned int reg)
 {
 	switch (reg >> SC16IS7XX_REG_SHIFT) {
 	case SC16IS7XX_RHR_REG:
+	case SC16IS7XX_IER_REG: /* Shared address space with DLH */
 	case SC16IS7XX_IIR_REG:
+	case SC16IS7XX_MCR_REG: /* Shared address space with XON1 */
 	case SC16IS7XX_LSR_REG:
 	case SC16IS7XX_MSR_REG:
 	case SC16IS7XX_TXLVL_REG:
-- 
2.53.0