[PATCH] net: phy: allow scanning busses with missing phys

[PATCH] net: phy: allow scanning busses with missing phys

[Alexandre Belloni]

Some MDIO busses will error out when trying to read a phy address with no
phy present at that address. In that case, probing the bus will fail
because __mdiobus_register() is scanning the bus for all possible phys
addresses.

In case MII_PHYSID1 returns -EIO or -ENODEV, consider there is no phy at
this address and set the phy ID to 0xffffffff which is then properly
handled in get_phy_device().

Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
---
 drivers/net/phy/phy_device.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index ac23322a32e1..9e4ba8e80a18 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -535,8 +535,17 @@ static int get_phy_id(struct mii_bus *bus, int addr, u32 *phy_id,
 
 	/* Grab the bits from PHYIR1, and put them in the upper half */
 	phy_reg = mdiobus_read(bus, addr, MII_PHYSID1);
-	if (phy_reg < 0)
+	if (phy_reg < 0) {
+		/* if there is no device, return without an error so scanning
+		 * the bus works properly
+		 */
+		if (phy_reg == -EIO || phy_reg == -ENODEV) {
+			*phy_id = 0xffffffff;
+			return 0;
+		}
+
 		return -EIO;
+	}
 
 	*phy_id = (phy_reg & 0xffff) << 16;
 
-- 
2.17.0

Re: [PATCH] net: phy: allow scanning busses with missing phys

[Florian Fainelli]

On 04/24/2018 09:09 AM, Alexandre Belloni wrote:
> Some MDIO busses will error out when trying to read a phy address with no
> phy present at that address. In that case, probing the bus will fail
> because __mdiobus_register() is scanning the bus for all possible phys
> addresses.
> 
> In case MII_PHYSID1 returns -EIO or -ENODEV, consider there is no phy at
> this address and set the phy ID to 0xffffffff which is then properly
> handled in get_phy_device().

Humm, why not have your MDIO bus implementation do the scanning itself
in a reset() callback, which happens before probing the bus, and based
on the results, set phy_mask accordingly such that only PHYs present are
populated?

My only concern with your change is that we are having a special
treatment for EIO and ENODEV, so we must make sure MDIO bus drivers are
all conforming to that.

> 
> Suggested-by: Andrew Lunn <andrew@lunn.ch>
> Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
> ---
>  drivers/net/phy/phy_device.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index ac23322a32e1..9e4ba8e80a18 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -535,8 +535,17 @@ static int get_phy_id(struct mii_bus *bus, int addr, u32 *phy_id,
>  
>  	/* Grab the bits from PHYIR1, and put them in the upper half */
>  	phy_reg = mdiobus_read(bus, addr, MII_PHYSID1);
> -	if (phy_reg < 0)
> +	if (phy_reg < 0) {
> +		/* if there is no device, return without an error so scanning
> +		 * the bus works properly
> +		 */
> +		if (phy_reg == -EIO || phy_reg == -ENODEV) {
> +			*phy_id = 0xffffffff;
> +			return 0;
> +		}
> +
>  		return -EIO;
> +	}
>  
>  	*phy_id = (phy_reg & 0xffff) << 16;
>  
> 

-- 
Florian

Re: [PATCH] net: phy: allow scanning busses with missing phys

[Andrew Lunn]

On Tue, Apr 24, 2018 at 09:37:09AM -0700, Florian Fainelli wrote:
> 
> 
> On 04/24/2018 09:09 AM, Alexandre Belloni wrote:
> > Some MDIO busses will error out when trying to read a phy address with no
> > phy present at that address. In that case, probing the bus will fail
> > because __mdiobus_register() is scanning the bus for all possible phys
> > addresses.
> > 
> > In case MII_PHYSID1 returns -EIO or -ENODEV, consider there is no phy at
> > this address and set the phy ID to 0xffffffff which is then properly
> > handled in get_phy_device().
> 
> Humm, why not have your MDIO bus implementation do the scanning itself
> in a reset() callback, which happens before probing the bus, and based
> on the results, set phy_mask accordingly such that only PHYs present are
> populated?

Hi Florian

Seems a bit odd have the driver do this, when the core could.

> My only concern with your change is that we are having a special
> treatment for EIO and ENODEV, so we must make sure MDIO bus drivers are
> all conforming to that.
 
I don't see how it could be a problem. It used to be any error was a
real error, and would stop the bus from loading. It now means there is
nothing there. The only possible side effect is an mdio bus driver
might remain loaded without any devices if all reads return
ENODEV/EIO, were as before it would probably never load. 

	    Andrew

Re: [PATCH] net: phy: allow scanning busses with missing phys

[Florian Fainelli]

On 04/24/2018 11:01 AM, Andrew Lunn wrote:
> On Tue, Apr 24, 2018 at 09:37:09AM -0700, Florian Fainelli wrote:
>>
>>
>> On 04/24/2018 09:09 AM, Alexandre Belloni wrote:
>>> Some MDIO busses will error out when trying to read a phy address with no
>>> phy present at that address. In that case, probing the bus will fail
>>> because __mdiobus_register() is scanning the bus for all possible phys
>>> addresses.
>>>
>>> In case MII_PHYSID1 returns -EIO or -ENODEV, consider there is no phy at
>>> this address and set the phy ID to 0xffffffff which is then properly
>>> handled in get_phy_device().
>>
>> Humm, why not have your MDIO bus implementation do the scanning itself
>> in a reset() callback, which happens before probing the bus, and based
>> on the results, set phy_mask accordingly such that only PHYs present are
>> populated?
> 
> Hi Florian
> 
> Seems a bit odd have the driver do this, when the core could.

I could see arguments for doing it in either location, if this is done
in the driver, the driver is responsible for knowing what addresses will
respond, which does not seem to big of a stretch. If done by core, we
lift the driver from taking care of that. Either way is fine, really.

> 
>> My only concern with your change is that we are having a special
>> treatment for EIO and ENODEV, so we must make sure MDIO bus drivers are
>> all conforming to that.
>  
> I don't see how it could be a problem. It used to be any error was a
> real error, and would stop the bus from loading. It now means there is
> nothing there. The only possible side effect is an mdio bus driver
> might remain loaded without any devices if all reads return
> ENODEV/EIO, were as before it would probably never load. 

Right, though that does not seem to be a big problem.

> 
> 	    Andrew
> 


-- 
Florian

Re: [PATCH] net: phy: allow scanning busses with missing phys

[Alexandre Belloni]

On 24/04/2018 09:37:09-0700, Florian Fainelli wrote:
> 
> 
> On 04/24/2018 09:09 AM, Alexandre Belloni wrote:
> > Some MDIO busses will error out when trying to read a phy address with no
> > phy present at that address. In that case, probing the bus will fail
> > because __mdiobus_register() is scanning the bus for all possible phys
> > addresses.
> > 
> > In case MII_PHYSID1 returns -EIO or -ENODEV, consider there is no phy at
> > this address and set the phy ID to 0xffffffff which is then properly
> > handled in get_phy_device().
> 
> Humm, why not have your MDIO bus implementation do the scanning itself
> in a reset() callback, which happens before probing the bus, and based
> on the results, set phy_mask accordingly such that only PHYs present are
> populated?
> 
> My only concern with your change is that we are having a special
> treatment for EIO and ENODEV, so we must make sure MDIO bus drivers are
> all conforming to that.
> 

That was what I was doing in [1] but it seems that Andrew preferred this way.

The third solution I was seeing was to return phy_reg instead of -EIO so
the MDIO driver can return -ENODEV and that would be passed to
get_phy_device(). __mdiobus_register() seems to handle -ENODEV properly.

My coccinelle-fu is not great but the following drivers can return
-ENODEV from their read callback:

drivers/net/ethernet/marvell/mvmdio.c
drivers/net/ethernet/hisilicon/hix5hd2_gmac.c (seeing the error message,
this has probably been copy pasted)

[1] https://marc.info/?l=linux-netdev&m=152183609927933&w=2

> > 
> > Suggested-by: Andrew Lunn <andrew@lunn.ch>
> > Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
> > ---
> >  drivers/net/phy/phy_device.c | 11 ++++++++++-
> >  1 file changed, 10 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> > index ac23322a32e1..9e4ba8e80a18 100644
> > --- a/drivers/net/phy/phy_device.c
> > +++ b/drivers/net/phy/phy_device.c
> > @@ -535,8 +535,17 @@ static int get_phy_id(struct mii_bus *bus, int addr, u32 *phy_id,
> >  
> >  	/* Grab the bits from PHYIR1, and put them in the upper half */
> >  	phy_reg = mdiobus_read(bus, addr, MII_PHYSID1);
> > -	if (phy_reg < 0)
> > +	if (phy_reg < 0) {
> > +		/* if there is no device, return without an error so scanning
> > +		 * the bus works properly
> > +		 */
> > +		if (phy_reg == -EIO || phy_reg == -ENODEV) {
> > +			*phy_id = 0xffffffff;
> > +			return 0;
> > +		}
> > +
> >  		return -EIO;
> > +	}
> >  
> >  	*phy_id = (phy_reg & 0xffff) << 16;
> >  
> > 
> 
> -- 
> Florian

-- 
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

Re: [PATCH] net: phy: allow scanning busses with missing phys

[Florian Fainelli]

On 04/24/2018 09:09 AM, Alexandre Belloni wrote:
> Some MDIO busses will error out when trying to read a phy address with no
> phy present at that address. In that case, probing the bus will fail
> because __mdiobus_register() is scanning the bus for all possible phys
> addresses.
> 
> In case MII_PHYSID1 returns -EIO or -ENODEV, consider there is no phy at
> this address and set the phy ID to 0xffffffff which is then properly
> handled in get_phy_device().
> 
> Suggested-by: Andrew Lunn <andrew@lunn.ch>
> Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
-- 
Florian

Re: [PATCH] net: phy: allow scanning busses with missing phys

[David Miller]

From: Alexandre Belloni <alexandre.belloni@bootlin.com>
Date: Tue, 24 Apr 2018 18:09:04 +0200

> Some MDIO busses will error out when trying to read a phy address with no
> phy present at that address. In that case, probing the bus will fail
> because __mdiobus_register() is scanning the bus for all possible phys
> addresses.
> 
> In case MII_PHYSID1 returns -EIO or -ENODEV, consider there is no phy at
> this address and set the phy ID to 0xffffffff which is then properly
> handled in get_phy_device().
> 
> Suggested-by: Andrew Lunn <andrew@lunn.ch>
> Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Applied, thank you.