netdev - Re: [PATCH 2/2 net-next] net: stmmac: Improve documentation on AVB parameters

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Date:   Fri, 7 Jul 2017 09:54:00 +0100
From:   Joao Pinto <Joao.Pinto@...opsys.com>
To:     Giuseppe CAVALLARO <peppe.cavallaro@...com>,
        Joao Pinto <Joao.Pinto@...opsys.com>, <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>, <alexandre.torgue@...com>
Subject: Re: [PATCH 2/2 net-next] net: stmmac: Improve documentation on AVB
 parameters


Hi Peppe,

Às 8:09 AM de 7/7/2017, Giuseppe CAVALLARO escreveu:
> Hi Joao
> 
> On 7/5/2017 12:34 PM, Joao Pinto wrote:
>> Hi Peppe,
>>
>> Às 8:10 AM de 6/9/2017, Giuseppe CAVALLARO escreveu:
>>> Hi Joao
>>>
>>> On 6/8/2017 8:02 PM, Joao Pinto wrote:
>>>> This patch fixes the description of the DT AVB parameters and gives
>>>> an accurate example. It was also included the base values that were
>>>> used to get the example' CBS paremeter values.
>>>>
>>>> Signed-off-by: Joao Pinto<jpinto@...opsys.com>
>>>> ---
>>>>    Documentation/devicetree/bindings/net/stmmac.txt | 24 ++++++++++++++++--------
>>>>    1 file changed, 16 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/net/stmmac.txt
>>>> b/Documentation/devicetree/bindings/net/stmmac.txt
>>>> index c3a7be6..707426d 100644
>>>> --- a/Documentation/devicetree/bindings/net/stmmac.txt
>>>> +++ b/Documentation/devicetree/bindings/net/stmmac.txt
>>>> @@ -109,10 +109,10 @@ Optional properties:
>>>>                  [Attention] Queue 0 is reserved for legacy traffic
>>>>                  and so no AVB is available in this queue.
>>>>            - Configure Credit Base Shaper (if AVB Mode selected):
>>>> -            - snps,send_slope: enable Low Power Interface
>>>> -            - snps,idle_slope: unlock on WoL
>>>> -            - snps,high_credit: max write outstanding req. limit
>>>> -            - snps,low_credit: max read outstanding req. limit
>>>> +            - snps,send_slope: Send Slope Credit value
>>>> +            - snps,idle_slope:  Idle Slope Credit value
>>>> +            - snps,high_credit: High Credit value
>>>> +            - snps,low_credit: Low Credit value
>>>>            - snps,priority: TX queue priority (Range: 0x0 to 0xF)
>>>>    Examples:
>>>>    @@ -143,10 +143,18 @@ Examples:
>>>>              queue1 {
>>>>                snps,avb-algorithm;
>>>> -            snps,send_slope = <0x1000>;
>>>> -            snps,idle_slope = <0x1000>;
>>>> -            snps,high_credit = <0x3E800>;
>>>> -            snps,low_credit = <0xFFC18000>;
>>>> +            /*
>>>> +             *  Example AVB parameters based on:
>>>> +             *   Allocated Bandwidth: 40%
>>>> +             *   Maximum Frame size: 1000 bytes
>>>> +             *   Maximum Interference size: 1500 bytes
>>>> +             *   Port Transmit Rate: 8
>>>> +             *   Scaling Factor: 1024
>>>> +             */
>>>> +            snps,idle_slope = <0xCCC>;
>>>> +            snps,send_slope = <0x1333>;
>>>> +            snps,high_credit = <0x4B0000>;
>>> Thanks for having taken care about this changes, please, as required, add a
>>> cover-letter
>>> and give more information about these values that can be tuned by user and, for
>>> example,
>>> the snps,high_credit could be as default = 0xbe4000 that is a reasonable value
>>> because
>>> comes from 1522 * 8 * 1024 and LOW credit is the two complement.
>>>                        ^^^^^
>>>                      frame size ---> maximum is 16
>> I calculate the hi credit this way:
>>
>>    HiCredit = BW / 100 * MaxInterferenceSize * 8 * Scaling
>>
>> Can I assume that you are considering 100% bandwidth for this example channel?
>> If so, it is not correct, since the maximum bandwidth should be 75%, leaving at
>> least 25% for default channel 0 (I think this is assured in the hardware).
> 
> ok, I did not remember that so I let you detail with a right example this part 
> in the doc.
> 
> Well done and thanks.

No problem! I will send an example soon. Thanks.

Joao

> 
> Peppe
> 
>> Thanks,
>> Joao
>>
>>> Regards
>>> Peppe
>>>
>>>> +            snps,low_credit = <0xFFB50000>;
>>>>                snps,priority = <0x1>;
>>>>            };
>>>>        };
>>>
>>
>