[PATCH v2] i2c: mediatek: fix WRRD for SoCs without auto_restart option

[PATCH v2] i2c: mediatek: fix WRRD for SoCs without auto_restart option

[Roman Vivchar via B4 Relay]

From: Roman Vivchar <rva333@protonmail.com>

MediaTek mt65xx family SoCs have no auto restart, however, they still
support the WRRD mode in the hardware. Because auto_restart is set to 0,
the WRRD mode will be never enabled, leading to read errors.

Fix this by removing auto_restart check from the WRRD enable path.

Fixes: b49218365280 ("i2c: mediatek: fix potential incorrect use of I2C_MASTER_WRRD")
Cc: stable@vger.kernel.org
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Roman Vivchar <rva333@protonmail.com>
---
This is a preparation for the mt6572/6595 upstreaming.

mt65xx family SoCs don't have auto restart, but vendor kernels keep using
WRRD mode. Lack of the WRRD mode makes i2c reads impossible from both
userspace and kernel drivers.

Without patch (mt6595, da9210 buck at 0x68):
~ # i2cget -y 1 0x68 0x00
Error: Read failed
~ # i2cget -y 1 0x68 0x01
Error: Read failed

With patch:
~ # i2cget -y 1 0x68 0x00
0x80
~ # i2cget -y 1 0x68 0x01
0x00

Same behavior observed on mt6572 devices.

This change doesn't affect SoCs with auto restart option.
---
Changes in v2:
- Add Fixes and Reviewed-by tags
- Add Cc stable
- Link to v1: https://patch.msgid.link/20260624-6572-6595-i2c-v1-1-9155cebaae20@protonmail.com
---
 drivers/i2c/busses/i2c-mt65xx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-mt65xx.c b/drivers/i2c/busses/i2c-mt65xx.c
index 126040ca05f1..307925fb78e3 100644
--- a/drivers/i2c/busses/i2c-mt65xx.c
+++ b/drivers/i2c/busses/i2c-mt65xx.c
@@ -1258,7 +1258,7 @@ static int mtk_i2c_transfer(struct i2c_adapter *adap,
 	i2c->auto_restart = i2c->dev_comp->auto_restart;
 
 	/* checking if we can skip restart and optimize using WRRD mode */
-	if (i2c->auto_restart && num == 2) {
+	if (num == 2) {
 		if (!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
 		    msgs[0].addr == msgs[1].addr) {
 			i2c->auto_restart = 0;

---
base-commit: 8cd9520d35a6c38db6567e97dd93b1f11f185dc6
change-id: 20260623-6572-6595-i2c-6ec9c4e6a6a6

Best regards,
--  
Roman Vivchar <rva333@protonmail.com>

Re: [PATCH v2] i2c: mediatek: fix WRRD for SoCs without auto_restart option

[Andi Shyti]

Hi Roman,

On Thu, Jul 09, 2026 at 04:31:29PM +0300, Roman Vivchar via B4 Relay wrote:
> From: Roman Vivchar <rva333@protonmail.com>
> 
> MediaTek mt65xx family SoCs have no auto restart, however, they still
> support the WRRD mode in the hardware. Because auto_restart is set to 0,
> the WRRD mode will be never enabled, leading to read errors.
> 
> Fix this by removing auto_restart check from the WRRD enable path.
> 
> Fixes: b49218365280 ("i2c: mediatek: fix potential incorrect use of I2C_MASTER_WRRD")
> Cc: stable@vger.kernel.org
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> Signed-off-by: Roman Vivchar <rva333@protonmail.com>

merged to i2c/i2c-fixes.

Thanks,
Andi