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

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Date:	Thu, 7 Jul 2016 15:58:57 -0700
From:	Iyappan Subramanian <isubramanian@....com>
To:	Russell King - ARM Linux <linux@...linux.org.uk>
Cc:	Andrew Lunn <andrew@...n.ch>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>, patches <patches@....com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	David Miller <davem@...emloft.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 3/5] drivers: net: phy: Add MDIO driver

Hi Russell,

On Thu, Jul 7, 2016 at 7:14 AM, Russell King - ARM Linux
<linux@...linux.org.uk> wrote:
> On Thu, Jul 07, 2016 at 04:03:02PM +0200, Andrew Lunn wrote:
>> > Wed, Jul 06, 2016 at 04:44:44PM -0700, Iyappan Subramanian wrote:
>> > Hi Andrew,
>> >
>> > On Tue, Jul 5, 2016 at 6:49 AM, Andrew Lunn <andrew@...n.ch> wrote:
>> > > 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?
>> >
>> > Hardware requires a clock pulse.  There is no bug.
>>
>> And how are you guaranteeing a pulse? You enable/disable/enable
>> without any sleeps, so it could all happen within a single clock
>> cycle?
>
> It's still really not good, because it does this:
>
> - prepare + enable
> - disable + unprepare
> - prepare + enable
>
> So every time the reset function is called, the prepare and enable
> counts against the clock get incremented.  That's a bug.  This needs
> a better solution.

I'll fix this by adding disable + unprepare on the port shutdown and
resubmit the patches.

>
> --
> RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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