netdev - Re: [PATCH v2 3/5] drivers: net: phy: Add MDIO driver

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Date:	Tue, 5 Jul 2016 15:49:50 +0200
From:	Andrew Lunn <andrew@...n.ch>
To:	Iyappan Subramanian <isubramanian@....com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, patches <patches@....com>,
	Matthias Brugger <matthias.bgg@...il.com>
Subject: Re: [PATCH v2 3/5] drivers: net: phy: Add MDIO driver

On Mon, Jun 06, 2016 at 10:12:35AM -0700, Iyappan Subramanian wrote:
> Hi Andrew,
> 
> Thanks for the review.
> 
> On Tue, May 31, 2016 at 6:11 PM, Andrew Lunn <andrew@...n.ch> wrote:
> > On Tue, May 31, 2016 at 05:10:38PM -0700, Iyappan Subramanian wrote:
> >> +static int xgene_mdio_reset(struct xgene_mdio_pdata *pdata)
> >> +{
> >> +     int ret;
> >> +
> >> +     if (pdata->mdio_id == XGENE_MDIO_RGMII) {
> >> +             if (pdata->dev->of_node) {
> >> +                     clk_prepare_enable(pdata->clk);
> >> +                     clk_disable_unprepare(pdata->clk);
> >> +                     clk_prepare_enable(pdata->clk);
> >
> > Hi Iyappan
> >
> > Is that a workaround for a hardware problem? If so, i would suggest
> > adding a comment, to stop people submitting a patch simplifying it.
> 
> Hardware expects this clock sequence.  I'll add comment as you suggested.

What exactly does the hardware require? Is this a workaround for a bug
in the clock generator? Or a workaround for a bug in the MDIO device?

If it is a clock generator bug, i think the fix should be in the clock
driver. If this is bug in the MDIO device, do you need a sleep in
there, so you actually have the clock ticking/not ticking for a time?
Since these calls can all sleep, you have no idea how long/sort the
clock will be enabled/disabled.

      Andrew