[PATCH] Net: add mdio_i2c driver.

Clément Leger cleger at kalray.eu
Fri Nov 17 01:34:07 PST 2017

----- Mail original -----
> De: "Sascha Hauer" <s.hauer at pengutronix.de>
> À: "Clément Leger" <cleger at kalray.eu>
> Cc: "Barebox List" <barebox at lists.infradead.org>
> Envoyé: Vendredi 17 Novembre 2017 10:06:58
> Objet: Re: [PATCH] Net: add mdio_i2c driver.

> On Fri, Nov 17, 2017 at 09:52:14AM +0100, Clément Leger wrote:
>> Hi Sascha,
>> Indeed, I though about that and I was facing another problem.
>> The mdio to i2c driver does not have a specific address.
>> ie, it is not a device but rather a bus.
>> If I put the mdio_i2c  node under the i2c bus, then I should assign
>> it an i2c address. This address should represent the phy address.
>> However, this would means I would have one mdio-i2c driver per phy.
> Some AT24 EEPROMs have the same problem, they also use multiple
> addresses. AFAIK for them only the first address is provided in the
> "reg" property. See drivers/eeprom/at24c.c how the driver handles this
> situation.

>From what I see, they just create a bunch of i2c device according to
the number of address to take.
In the case of mdio-i2c, we do not know in advance how many phy will
be hidden behind the bus. I think I will have to go with the double
address description.
This will also avoid spurious i2c write by bus scanning done by phy
detection layer.

> Normally I think multi address devices should simply provide their
> reg space as reg = <start size>; like other devices do aswell. I don't
> know what the I2C core maked from this though.

It will not work and will not even compile (with dtc errors activated)
since the i2c controllers are almost always describe as:

  #address-cells = <1>;
  #size-cells = <0>;

So no size cell.

If you agree, I will go with the double device address (both in mdio-i2c and phy)


> Sascha
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