Re: [PATCH net-next 1/2] ethtool: add PHY Fast Link Down support

[Heiner Kallweit <hkallweit1@gmail.com>]

On 26.03.2019 09:24, Andrew Lunn wrote:
>>> +#define ETHTOOL_PHY_FAST_LINK_DOWN_ON	0
>>> +#define ETHTOOL_PHY_FAST_LINK_DOWN_OFF	0xff
>>> +
>>>  enum phy_tunable_id {
>>>  	ETHTOOL_PHY_ID_UNSPEC,
>>>  	ETHTOOL_PHY_DOWNSHIFT,
>>> +	ETHTOOL_PHY_FAST_LINK_DOWN,
>>>  	/*
>>>  	 * Add your fresh new phy tunable attribute above and remember to update
>>>  	 * phy_tunable_strings[] in net/core/ethtool.c
>>
>> It would be nice to have a short summary around here explaining how is
>> the value interpreted. While it's obvious from the second patch, one
>> shouldn't have to go into driver specific implementation to find out.
>>
>> I also wonder if the range 0-254 ms is sufficient. Would it be possible
>> that there is some other hardware which would support e.g. 300 ms?
> 
> The default, as defined by the 802.3 standard, is i think 750ms.
> 
Clause 40. From what I've found this applies to 1000BaseT only.

> The Marvel PHY also supports 50ms, 20ms and 0ms, if i remember
> correctly.
> 
0, 10, 20, 40ms (at least for 88E1540 and 88E6390)

> One problem we have here is discovery. How does the user find out the
> values the driver supports. For a netlink socket API, extended errors
> could be used to pass back a string indicating the supported
> values. For the old ethtool, i think all we have is -EINVAL, which is
> not very helpful.
> 
> 	Andrew
> .
> 
Heiner