linux-kernel - Re: [PATCH v4.1] phylib: Add device reset GPIO support

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Date:   Thu, 7 Dec 2017 20:40:37 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Geert Uytterhoeven <geert+renesas@...der.be>,
        "David S . Miller" <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Simon Horman <horms@...ge.net.au>,
        Magnus Damm <magnus.damm@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Richard Leitner <richard.leitner@...data.com>,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4.1] phylib: Add device reset GPIO support

On 12/07/2017 08:20 PM, Sergei Shtylyov wrote:

>> The PHY devices sometimes do have their reset signal (maybe even power
>> supply?) tied to some GPIO and sometimes it also does happen that a boot
>> loader does not leave it deasserted. So far this issue has been attacked
>> from (as I believe) a wrong angle: by teaching the MAC driver to manipulate
>> the GPIO in question; that solution, when applied to the device trees, led
>> to adding the PHY reset GPIO properties to the MAC device node, with one
>> exception: Cadence MACB driver which could handle the "reset-gpios" prop
>> in a PHY device subnode. I believe that the correct approach is to teach
>> the 'phylib' to get the MDIO device reset GPIO from the device tree node
>> corresponding to this device -- which this patch is doing...
>>
>> Note that I had to modify the AT803x PHY driver as it would stop working
>> otherwise -- it made use of the reset GPIO for its own purposes...
>>
>> Signed-off-by: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
>> Acked-by: Rob Herring <robh@...nel.org>
>> [geert: Propagate actual errors from fwnode_get_named_gpiod()]
>> [geert: Avoid destroying initial setup]
>> [geert: Consolidate GPIO descriptor acquiring code]
>> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> [...]
>> diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
>> index 2df7b62c1a36811e..8f8b7747c54bc478 100644
>> --- a/drivers/net/phy/mdio_bus.c
>> +++ b/drivers/net/phy/mdio_bus.c
> [...]
>> @@ -48,9 +49,26 @@
>>   int mdiobus_register_device(struct mdio_device *mdiodev)
>>   {
>> +    struct gpio_desc *gpiod = NULL;
>> +
>>       if (mdiodev->bus->mdio_map[mdiodev->addr])
>>           return -EBUSY;
>> +    /* Deassert the optional reset signal */
> 
>     Umm, but why deassert it here for such a short time?
> 
>> +    if (mdiodev->dev.of_node)
>> +        gpiod = fwnode_get_named_gpiod(&mdiodev->dev.of_node->fwnode,
>> +                           "reset-gpios", 0, GPIOD_OUT_LOW,
>> +                           "PHY reset");
>> +    if (PTR_ERR(gpiod) == -ENOENT)
>> +        gpiod = NULL;
>> +    else if (IS_ERR(gpiod))
>> +        return PTR_ERR(gpiod);
> 
>     Hm, returning on error with reset deasserted?

    Oops, error means we couldn't drive the GPIO at all...
    The 1st question remains though...

[...]

MBR, Sergei