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

[Sergei Shtylyov]

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@xxxxxxxxxxxxxxxxxx>
> > > 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@xxxxxxxxxxxxxxxxxx>
> > > Acked-by: Rob Herring <robh@xxxxxxxxxx>
> > > [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@xxxxxxxxx>
> >
> > [...]
> > > 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