Re: [PATCH net-next 1/2] net: phy: Add Speed downshift set driver for Microsemi PHYs.

Hi Florian,

Thank you for review comments.

On Mon, Oct 17, 2016 at 05:38:46AM -0700, Florian Fainelli wrote:

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On October 17, 2016 12:31:54 AM PDT, Raju Lakkaraju [off-list ref] wrote:

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Hi Andrew,

Thank you for code review and comments.

On Fri, Oct 14, 2016 at 02:12:32PM +0200, Andrew Lunn wrote:

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On Fri, Oct 14, 2016 at 05:10:32PM +0530, Raju Lakkaraju wrote:

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From: Raju Lakkaraju <redacted>

For operation in cabling environments that are incompatible with
1000BAST-T, VSC8531 device provides an automatic link speed
downshift operation. When enabled, the device automatically changes
its 1000BAST-T auto-negotiation to the next slower speed after
a configured number of failed attempts at 1000BAST-T.
This feature is useful in setting up in networks using older cable
installations that include only pairs A and B, and not pairs C and

D.

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Any reason not to just turn this on by default when auto-neg is
enabled?

Downshift can enable by default when auto-neg enabled. This is good
idea.
But we would like to provide option to customer can choose whether this
feature need to enable or disable and also configure failure attempts.

Do you have any other suggestion how to configure failure attempts?

Is the speed downshift feature similar to what Intel and Broadcom refer to as wirespeed? I have seen cases with Broadcom PHYs where we had to turn such a feature on to allow auto-negotiation to complete with 4-wire cables, but this had the downside of impacting normal autoneg, so it is left disabled.

Yes. I check the Broadcom wirespeed code. Downshift is similar to wirespeed.
But Broadcom wirespeed configuration in Ethernet controller. 

I would expect the number of customers using this feature to be fairly limited, so having a tunable to turn this downshift on/off may be acceptable. Ethtool supports a number of tunable parameters now (such as rx_copybreak), there may be room for using something similar for boolean flags like these.

This implementation shows little bit specific to Ethernet controller.
Do you have any PHY specific examples?

In another mail thread, you proposed similar to net device features.
Shall i implement that suggestion here?

--
Florian

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Thanks,
Raju.