[PATCH] net: phy: marvell: Fix bits clear bug

[PATCH] net: phy: marvell: Fix bits clear bug

[Hansen Yang]

The correct way to clear bits before setting some of them is using
"& = ~BIT_MASK".
The wrong operation "& = BIT_MASK" will clear other bits.

m88e1116r_config_init() calls marvell_set_polarity() to config
MDI crossover mode by modifying reg MII_M1011_PHY_SCR, then it
calls marvell_set_downshift() to config downshift by modifying
the same reg. According to the bug, marvell_set_downshift()
clears other bits and set MDI Crossover Mode to Manual MDI
configuration. If we connect two devices both using this driver
with a wrong Ethernet cable, they can't automatically adjust
their crossover mode. Finally they fail to link.

Signed-off-by: Hansen Yang <yanghansen1@163.com>
---
 drivers/net/phy/marvell.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/phy/marvell.c b/drivers/net/phy/marvell.c
index a7796134e3be..6ab8fe339043 100644
--- a/drivers/net/phy/marvell.c
+++ b/drivers/net/phy/marvell.c
@@ -282,7 +282,7 @@ static int marvell_set_downshift(struct phy_device *phydev, bool enable,
 	if (reg < 0)
 		return reg;
 
-	reg &= MII_M1011_PHY_SRC_DOWNSHIFT_MASK;
+	reg &= ~MII_M1011_PHY_SRC_DOWNSHIFT_MASK;
 	reg |= ((retries - 1) << MII_M1011_PHY_SCR_DOWNSHIFT_SHIFT);
 	if (enable)
 		reg |= MII_M1011_PHY_SCR_DOWNSHIFT_EN;
-- 
2.17.1

Re: [PATCH] net: phy: marvell: Fix bits clear bug

[Heiner Kallweit]

On 02.11.2019 15:15, Hansen Yang wrote:
> The correct way to clear bits before setting some of them is using
> "& = ~BIT_MASK".
> The wrong operation "& = BIT_MASK" will clear other bits.
> 
> m88e1116r_config_init() calls marvell_set_polarity() to config
> MDI crossover mode by modifying reg MII_M1011_PHY_SCR, then it
> calls marvell_set_downshift() to config downshift by modifying
> the same reg. According to the bug, marvell_set_downshift()
> clears other bits and set MDI Crossover Mode to Manual MDI
> configuration. If we connect two devices both using this driver
> with a wrong Ethernet cable, they can't automatically adjust
> their crossover mode. Finally they fail to link.
> 
Function marvell_set_downshift() doesn't exist any longer.
Note that all new developments should be against net-next.

If you want to submit this as a fix for stable:
- annotate patch as [PATCH net]
- add Fixes tag
- mention that fix applies up to 5.4 only

> Signed-off-by: Hansen Yang <yanghansen1@163.com>
> ---
>  drivers/net/phy/marvell.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/phy/marvell.c b/drivers/net/phy/marvell.c
> index a7796134e3be..6ab8fe339043 100644
> --- a/drivers/net/phy/marvell.c
> +++ b/drivers/net/phy/marvell.c
> @@ -282,7 +282,7 @@ static int marvell_set_downshift(struct phy_device *phydev, bool enable,
>  	if (reg < 0)
>  		return reg;
>  
> -	reg &= MII_M1011_PHY_SRC_DOWNSHIFT_MASK;
> +	reg &= ~MII_M1011_PHY_SRC_DOWNSHIFT_MASK;
>  	reg |= ((retries - 1) << MII_M1011_PHY_SCR_DOWNSHIFT_SHIFT);
>  	if (enable)
>  		reg |= MII_M1011_PHY_SCR_DOWNSHIFT_EN;
> 

Heiner