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
[off-list ref] wrote:

On Thu, Jul 07, 2016 at 04:03:02PM +0200, Andrew Lunn wrote:

quoted

quoted

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 [off-list ref] wrote:

quoted

On Mon, Jun 06, 2016 at 10:12:35AM -0700, Iyappan Subramanian wrote:

quoted

Hi Andrew,

Thanks for the review.

On Tue, May 31, 2016 at 6:11 PM, Andrew Lunn [off-list ref] wrote:

quoted

On Tue, May 31, 2016 at 05:10:38PM -0700, Iyappan Subramanian wrote:

quoted

+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.

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