netdev - Re: [PATCH net-next v2 2/4] Documentation: net: phy: Add a paragraph about pause frames/flow control

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Date:   Mon, 28 Nov 2016 09:33:34 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Sebastian Frias <sf84@...oste.net>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, andrew@...n.ch,
        martin.blumenstingl@...glemail.com, mans@...sr.com,
        alexandre.torgue@...com, peppe.cavallaro@...com,
        timur@...eaurora.org, jbrunet@...libre.com
Subject: Re: [PATCH net-next v2 2/4] Documentation: net: phy: Add a paragraph
 about pause frames/flow control

On 11/28/2016 02:38 AM, Sebastian Frias wrote:
> On 27/11/16 19:44, Florian Fainelli wrote:
>> Describe that the Ethernet MAC controller is ultimately responsible for
>> dealing with proper pause frames/flow control advertisement and
>> enabling, and that it is therefore allowed to have it change
>> phydev->supported/advertising with SUPPORTED_Pause and
>> SUPPORTED_AsymPause.
>>
>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>> ---
>>  Documentation/networking/phy.txt | 18 ++++++++++++++++--
>>  1 file changed, 16 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/networking/phy.txt b/Documentation/networking/phy.txt
>> index 4b25c0f24201..9a42a9414cea 100644
>> --- a/Documentation/networking/phy.txt
>> +++ b/Documentation/networking/phy.txt
>> @@ -127,8 +127,9 @@ Letting the PHY Abstraction Layer do Everything
>>   values pruned from them which don't make sense for your controller (a 10/100
>>   controller may be connected to a gigabit capable PHY, so you would need to
>>   mask off SUPPORTED_1000baseT*).  See include/linux/ethtool.h for definitions
>> - for these bitfields. Note that you should not SET any bits, or the PHY may
>> - get put into an unsupported state.
>> + for these bitfields. Note that you should not SET any bits, except the
>> + SUPPORTED_Pause and SUPPORTED_AsymPause bits (see below), or the PHY may get
>> + put into an unsupported state.
>>  
>>   Lastly, once the controller is ready to handle network traffic, you call
>>   phy_start(phydev).  This tells the PAL that you are ready, and configures the
>> @@ -139,6 +140,19 @@ Letting the PHY Abstraction Layer do Everything
>>   When you want to disconnect from the network (even if just briefly), you call
>>   phy_stop(phydev).
>>  
>> +Pause frames / flow control
>> +
>> + The PHY does not participate directly in flow control/pause frames except by
>> + making sure that the SUPPORTED_Pause and SUPPORTED_AsymPause bits are set in
>> + MII_ADVERTISE to indicate towards the link partner that the Ethernet MAC
>> + controller supports such a thing. Since flow control/pause frames generation
>> + involves the Ethernet MAC driver, it is recommended that this driver takes care
>> + of properly indicating advertisement and support for such features by setting
>> + the SUPPORTED_Pause and SUPPORTED_AsymPause bits accordingly. This can be done
>> + either before or after phy_connect() 
> 
> If the bits are set after phy_connect(), how does the PHY framework knows there's
> an update to the bits? Should some call be made?

You would most likely either call phy_start() to start the PHY state
machine (again) or have to re-negotiate the link with e.g:
genphy_restart_aneg().
-- 
Florian