On October 17, 2016 12:31:54 AM PDT, Raju Lakkaraju <raju.lakkar...@microsemi.com> wrote: >Hi Andrew, > >Thank you for code review and comments. > >On Fri, Oct 14, 2016 at 02:12:32PM +0200, Andrew Lunn wrote: >> EXTERNAL EMAIL >> >> >> On Fri, Oct 14, 2016 at 05:10:32PM +0530, Raju Lakkaraju wrote: >> > From: Raju Lakkaraju <raju.lakkar...@microsemi.com> >> > >> > 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. >> >> 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. 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. -- Florian