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SubjectRe: [PATCH v3 net-next] mdio_bus: Issue GPIO RESET to PHYs.
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Hi Florian,

On 21/04/17 04:23, Florian Fainelli wrote:
> Hi Roger,
>
> On 04/20/2017 07:11 AM, Roger Quadros wrote:
>> Some boards [1] leave the PHYs at an invalid state
>> during system power-up or reset thus causing unreliability
>> issues with the PHY which manifests as PHY not being detected
>> or link not functional. To fix this, these PHYs need to be RESET
>> via a GPIO connected to the PHY's RESET pin.
>>
>> Some boards have a single GPIO controlling the PHY RESET pin of all
>> PHYs on the bus whereas some others have separate GPIOs controlling
>> individual PHY RESETs.
>>
>> In both cases, the RESET de-assertion cannot be done in the PHY driver
>> as the PHY will not probe till its reset is de-asserted.
>> So do the RESET de-assertion in the MDIO bus driver.
>>
>> [1] - am572x-idk, am571x-idk, a437x-idk
>>
>> Signed-off-by: Roger Quadros <rogerq@ti.com>
>
> A few comments on the binding and the code, sorry for this late review.

No problem at all.
>
>> +Example :
>> +This example shows these optional properties, plus other properties
>> +required for the TI Davinci MDIO driver.
>> +
>> + davinci_mdio: ethernet@0x5c030000 {
>> + compatible = "ti,davinci_mdio";
>> + reg = <0x5c030000 0x1000>;
>> + #address-cells = <1>;
>> + #size-cells = <0>;
>> +
>> + reset-gpios = <&gpio2 5 GPIO_ACTIVE_LOW>;
>> + reset-delay-us = <2>; /* PHY datasheet states 1uS min */
>
> us is micro seconds, uS is micro siemens.

OK.

>
>> +
>> + ethphy0: ethernet-phy@1 {
>> + reg = <1>;
>> + };
>> +
>> + ethphy1: ethernet-phy@3 {
>> + reg = <3>;
>> + };
>> + };
>
>>
>> + /* de-assert bus level PHY GPIO resets */
>> + for (i = 0; i < bus->num_reset_gpios; i++) {
>> + gpiod = devm_gpiod_get_index(&bus->dev, "reset", i,
>> + GPIOD_OUT_LOW);
>> + if (IS_ERR(gpiod)) {
>> + err = PTR_ERR(gpiod);
>> + if (err != -ENOENT) {
>> + pr_err("mii_bus %s couldn't get reset GPIO\n",
>> + bus->id);
>
> Could we use dev_err(&bus->dev) here to better identify which MDIO bus
> is returning the problem?

Sure.
>
>> + return err;
>
> Should we somehow "unwind" the reset lines we were able to successfully
> take out of reset and therefore put back into reset state? How about
> mdiobus_unregister()? Should we have similar code there, if not for
> correctness to be more power efficient?

Al right.

>
>> + }
>> + } else {
>> + gpiod_set_value_cansleep(gpiod, 1);
>> + udelay(bus->reset_delay_us);
>> + gpiod_set_value_cansleep(gpiod, 0);
>
> Does that work even if the polarity of the reset line is active low?
>

Yes. The polarity needs to be specified at DT as explained by Andrew already.

cheers,
-roger

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