Re: [PATCH] [v2] power/fsl: add MDIO dt binding for FMan

Hello Scott,


On 12/22/2014 03:42 AM, Scott Wood wrote:

On Mon, 2014-12-22 at 03:37 -0600, Emil Medve wrote:

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Hello Scott,


On 12/22/2014 02:32 AM, Scott Wood wrote:

quoted

On Mon, 2014-12-22 at 02:20 -0600, Emil Medve wrote:

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For the purpose of an example in the binding document, I suggest we just
stick with the IEEE standard frequency.

The whole reason for this property existing in the device tree is
non-standard frequencies.

While the standard claims 2.5 MHz, most MDIO controllers and PHY devices
support frequencies well beyond the standard. Specifying a lower then
the standard frequency for the benefit of some errata is just one side
of this property

The erratum was (until now) the only claimed reason for it.  If there
are other reasons why one would specify a different frequency (in
particular, that relate to hardware description), please elaborate.

From memory, the 1 Gb/s Vitesse PHY(s) we have on some of our DS boards

support 12.5 MHz. I can dig out more specs for specifics on other PHY(s)

2.5 MHz is slow and even more so for high speed interfaces. With both
polling and interrupts (both MDIO and/or PHY) we've noticed (or blamed)
in the past some Ethernet performance issues on this very slowness

As of right now I'm not aware of another way to specify/coordinate the
MDC speed so setting a default (common denominator) in the DT that is
different then the IEEE standard seems ok

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We can continue this conversation about errata handling when we submit
the code relevant to this binding (and the FMan v3 support)

It affects the binding, so let's discuss it now please.

I think this specific (unpublished yet) errata has less bearing on the
binding then you might believe. This is mostly about providing a
common/default frequency supported by all the devices on some board

What reason other than an erratum would there be for the standard
frequency not being supported?

This is not about not supporting the standard frequency. This is about
the default frequency being different then the standard


Cheers,