netdev - RE: "asix: Don't reset PHY on if_up for ASIX 88772" breaks net on arndale platform

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Date:	Wed, 12 Nov 2014 10:49:36 +0100
From:	"Stam, Michel [FINT]" <M.Stam@...ro.nl>
To:	"Ben Hutchings" <ben@...adent.org.uk>,
	"Charles Keepax" <ckeepax@...nsource.wolfsonmicro.com>
Cc:	"Riku Voipio" <riku.voipio@....fi>, <davem@...emloft.net>,
	<linux-usb@...r.kernel.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-samsung-soc@...r.kernel.org>
Subject: RE: "asix: Don't reset PHY on if_up for ASIX 88772" breaks net on arndale platform

Hello Ben,

Regarding the code snippet;

Good question, The original code didn't do this either, which is why I left it as it is. It could cause undesirable behaviour, agreed.

After a quick driver examination: I do see that asix_set_sw_mii and asix_set_hw_mii are called prior to the actual write (asix_mdio_write), it may be that this takes care of ensuring data is written to the chip, as asix_write_cmd waits for usbnet_write_cmd to send (and acknowledge) a USB CONTROL MSG. A lock to the phy is held during this time.

If I recall my USB knowledge, control messages are acknowledged, which would ensure data is written to the chip. Whether the ASIX requires further delay I would not know. I would have to dive deeper into the timings of the ASIX chip and the driver behaviour to see if that would be the case.

Kind regards,

Michel Stam
-----Original Message-----
From: Ben Hutchings [mailto:ben@...adent.org.uk] 
Sent: Wednesday, November 12, 2014 1:23 AM
To: Charles Keepax
Cc: Stam, Michel [FINT]; Riku Voipio; davem@...emloft.net; linux-usb@...r.kernel.org; netdev@...r.kernel.org; linux-kernel@...r.kernel.org; linux-samsung-soc@...r.kernel.org
Subject: Re: "asix: Don't reset PHY on if_up for ASIX 88772" breaks net on arndale platform

On Tue, 2014-11-04 at 20:09 +0000, Charles Keepax wrote:
> On Tue, Nov 04, 2014 at 11:23:06AM +0100, Stam, Michel [FINT] wrote:
> > Hello Riku,
> > 
> > >Fixing a bug (ethtool support) must not cause breakage elsewhere 
> > >(in
> > this case on arndale). This is now a regression of functionality 
> > from 3.17.
> > >
> > >I think it would better to revert the change now and with less 
> > >hurry
> > introduce a ethtool fix that doesn't break arndale.
> > 
> > I don't fully agree here;
> > I would like to point out that this commit is a revert itself. 
> > Fixing the armdale will then cause breakage in other 
> > implementations, such as ours. Blankly reverting breaks other peoples' implementations.
> > 
> > The PHY reset is the thing that breaks ethtool support, so any fix 
> > that appeases all would have to take existing PHY state into account.
[...]
> --- a/drivers/net/usb/asix_devices.c
> +++ b/drivers/net/usb/asix_devices.c
> @@ -299,6 +299,7 @@ static int ax88772_reset(struct usbnet *dev)  {
>         struct asix_data *data = (struct asix_data *)&dev->data;
>         int ret, embd_phy;
> +       int reg;
>         u16 rx_ctl;
> 
>         ret = asix_write_gpio(dev,
> @@ -359,8 +360,10 @@ static int ax88772_reset(struct usbnet *dev)
>         msleep(150);
> 
>         asix_mdio_write(dev->net, dev->mii.phy_id, MII_BMCR, BMCR_RESET);
> -       asix_mdio_write(dev->net, dev->mii.phy_id, MII_ADVERTISE,
> -                       ADVERTISE_ALL | ADVERTISE_CSMA);
> +       reg = asix_mdio_read(dev->net, dev->mii.phy_id, MII_ADVERTISE);
> +       if (!reg)
> +               reg = ADVERTISE_ALL | ADVERTISE_CSMA;
> +       asix_mdio_write(dev->net, dev->mii.phy_id, MII_ADVERTISE, 
> + reg);
[...]

Why is there no sleep after setting the RESET bit?  Doesn't that make the following register writes unreliable?

Ben.

--
Ben Hutchings
Experience is directly proportional to the value of equipment destroyed.
                                                         - Carolyn Scheppner