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

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Message-ID: <188848c4-7159-55b2-07b2-0f8c1391a484@st.com>
Date:   Fri, 9 Jun 2017 09:10:33 +0200
From:   Giuseppe CAVALLARO <peppe.cavallaro@...com>
To:     Joao Pinto <Joao.Pinto@...opsys.com>, <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>, <alexandre.torgue@...com>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH 2/2 net-next] net: stmmac: Improve documentation on AVB
 parameters

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

Regards
Peppe

> +			snps,low_credit = <0xFFB50000>;
>   			snps,priority = <0x1>;
>   		};
>   	};