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

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Message-ID: <837cb555-f747-e8a8-ac1a-aa25ad213c0a@cogentembedded.com>
Date:   Fri, 8 Dec 2017 20:20:09 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     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>,
        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" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4.1] phylib: Add device reset GPIO support

Hello!

On 12/08/2017 12:53 PM, Geert Uytterhoeven wrote:

>> On 12/04/2017 03:35 PM, Geert Uytterhoeven wrote:
>>> From: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
>>> 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?
> 
> That's a consequence of moving it from drivers/of/of_mdio.c to here.

    Well, you shouldn't do code moves without some thinking. ;-)

> Not that it was deasserted that much longer in drivers/of/of_mdio.c, though...

    There it had a reason, here I'm not seeing one. Perhaps using GPIOD_ASIS 
(or GPIOD_OUT_HIGH) instead of GPIOD_OUT_LOW and dropping 
mdio_device_reset(mdiodev, 1) afterwards would make more sense here?

> Gr{oetje,eeting}s,
> 
>                          Geert

MBR, Sergei