Re: [RFT PATCH 1/2] net: dsa: mv88e6xxx: Add EEE support

[Florian Fainelli <f.fainelli@gmail.com>]

On 23/02/15 10:52, Guenter Roeck wrote:
> On Mon, Feb 23, 2015 at 09:45:01AM -0800, Florian Fainelli wrote:
>> On 23/02/15 08:26, Guenter Roeck wrote:
>>> EEE configuration is similar for the various MV88E6xxx chips.
>>> Add generic support for it.
>>>
>>> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
>>
>> Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
>>
>>> ---
>>> Applies to net-next.
>>>
>>> The code seems to be working, at least according to ethtool, but some
>>> more testing with other chip types would be useful. Also, I am not sure
>>> what to do with phy_init_eee.
>>
>> phy_init_eee() is to be used in case you have a PHY which is not managed
>> by the switch indirect or direct accesses, it looks like you are just
>> fine with the current code.
>>
>> One possible improvement could be ironing out the EEE
>> enabling/resolution by ensuring that the link partner also supports EEE?
>> Not sure if there is an existing register returning that from the
>> switch, or if you need to do a direct read to the PHY?
>>
> 
> EEE configuration on Marvell switches is independent from link partner
> capabilities. In the hardware available to me, EEE is enabled by
> default with a strapping pin on the chip. Making it dependent on link
> partner capabilities would be odd because it would mean that, if the
> link is down or if the link partner doesn't support it, it could be
> disabled, but it could no longer be re-enabled. This is what
> phy_init_eee enforces today. I dropped calling it because I thought
> that this behavior would be odd and inconsistent.
> 
> Question for me is if it makes sense to have phy_init_eee depend on
> the link status or on link partner capabilities in the first place.
> Personally I think it should only depend on local PHY capabilities,
> and that it should be possible to configure EEE even if the link
> is down or if the (current) link partner doesn't support it.

Completely agree with that.

BTW, the clock stop thing is also poorly handled imho because you would
want the PHY library to tell you whether your PHY supports TX clock
stopping, and not having to discover that by doing a first call with
phy_init_eee(phydev, 1), see that it fails, retry with
phy_init_eee(phydev, 0), but that's for another series of patches:

https://github.com/ffainelli/linux/tree/phy-eee-tx-clk

> 
> Consider the following: Assume both ends are configured to have EEE
> disabled, even if the PHYs support it. Both ends run linux and call
> phy_init_eee() to check for EEE capabilities. I have not tested it,
> but I suspect that it is not currently possible to enable EEE on either
> end because both ends believe that the link partner doesn't support it.
> I'll test that theory once I get a system where I can control both ends.

Well, it will work the first time you enable EEE and all of these
conditions are met: link is negotiated, your PHY reports EEE capability,
your link partner advertises EEE, and subsequent link up/down events
should maintain EEE operation. I agree that this needs revisiting
because you would certainly want to advertise EEE all the time if you
support it and have configured it, and enable it as soon as you find a
link partner that can also support EEE.
-- 
Florian