Re: [PATCH] Fix genphy_restart_aneg() for Micrel's ksz9031.

From: Sascha Hauer <s.hauer@pengutronix.de>
To: Guillermo Rodriguez Garcia <guille.rodriguez@gmail.com>
Cc: barebox@lists.infradead.org, Philipp Zabel <pza@pengutronix.de>,
	Trent Piepho <tpiepho@kymetacorp.com>
Subject: Re: [PATCH] Fix genphy_restart_aneg() for Micrel's ksz9031.
Date: Wed, 15 Jun 2016 07:49:10 +0200	[thread overview]
Message-ID: <20160615054910.GC9677@pengutronix.de> (raw)
In-Reply-To: <CABDcavasLdCoH5gxWMrysjyVnGd5K_F+2=gi6CS1Xmaegkib8g@mail.gmail.com>

On Tue, Jun 14, 2016 at 09:39:23AM +0200, Guillermo Rodriguez Garcia wrote:
> Hi Sascha,
> 
> 2016-06-14 8:39 GMT+02:00 Sascha Hauer <s.hauer@pengutronix.de>:
> > Hi Guillermo,
> >
> > On Mon, Jun 13, 2016 at 07:29:15PM +0200, Guillermo Rodriguez Garcia wrote:
> >> From: grodriguez <guille.rodriguez@gmail.com>
> >>
> >> Commit da89ee8f2e04 ("Center FLP timing at 16ms") breaks
> >> genphy_restart_aneg() for Micrel's ksz9031. According to the
> >> datasheet, the ksz9031 requires a wait of 1ms after clearing
> >> the PDOWN bit and before read/write access to any PHY registers.
> >> ---
> >>  drivers/net/phy/phy.c |    9 ++++++++-
> >>  1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > I must say that I am not overly happy with this patch as it leaks in phy
> > specific stuff into a somewhat generic function. Anyway, I see the need
> > for this patch and so I applied it.
> 
> Yes, I understand perfectly and I feel the same.
> The alternative was to create a custom genphy_restart_aneg for micrel
> PHYs only add the delay there, however I am not sure it is worth the
> trouble just for a 1ms delay which will be virtually unnoticeable
> anyway.

There's also the case when Micrel phy support is disabled. In this case
a Micrel phy is then handled by the generic phy, so we still need the
delay in the generic code, or we would have to remove the BMCR_PDOWN
setting from the generic code also.

> 
> Also I am not completely sure that this only applies to Micrel. See
> this for example in the SMSC911x driver from the Linux kernel:
> http://lxr.free-electrons.com/source/drivers/net/ethernet/smsc/smsc911x.c#L1364
> 
> Anyway if you would prefer this to be moved to micrel.c I would be
> happy to prepare a patch for that; just let me know.

Your patch is fine for now. Let's see what unforseen problems it
generates before changing it again ;)

Sascha

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