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

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