linux-kernel - RE: [PATCH v4 4/5] net: macb: add support for high speed interface

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Message-ID: <CO2PR07MB2469FDA06C3F8848290013B8C1E00@CO2PR07MB2469.namprd07.prod.outlook.com>
Date:   Mon, 24 Jun 2019 06:52:51 +0000
From:   Parshuram Raju Thombare <pthombar@...ence.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     "nicolas.ferre@...rochip.com" <nicolas.ferre@...rochip.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rafal Ciepiela <rafalc@...ence.com>,
        Anil Joy Varughese <aniljoy@...ence.com>,
        Piotr Sroka <piotrs@...ence.com>
Subject: RE: [PATCH v4 4/5] net: macb: add support for high speed interface

Hi Andrew,

>> +enum {
>> +	MACB_SERDES_RATE_5_PT_15625Gbps = 5,
>> +	MACB_SERDES_RATE_10_PT_3125Gbps = 10,
>> +};
>What do the units mean here? Why would you clock the SERDES at 15Tbps,
>or 3Tbps? 3.125Mbps would give you 2.5Gbps when using 8b/10b encoding.
>
MACB_SERDES_RATE_5_PT_15625Gbps is for 5.15625Gbps, I think this should be just
MACB_SERDES_RATE_5_Gbps and MACB_SERDES_RATE_10_Gbps. I will do it in next patch set.

>Xilinx documentation:
>https://urldefense.proofpoint.com/v2/url?u=https-
>3A__www.xilinx.com_support_documentation_ip-5Fdocumentation_usxgmii_v1-
>5F1_pg251-
>2Dusxgmii.pdf&d=DwIBAg&c=aUq983L2pue2FqKFoP6PGHMJQyoJ7kl3s3GZ-
>_haXqY&r=GTefrem3hiBCnsjCOqAuapQHRN8-rKC1FRbk0it-
>LDs&m=6V8fNIg49czRjfvVtDJ5BbR28p9UPlLLyB7fah7ypcw&s=LsDphgLBe1VDpM
>_K9pkuyal873WeKqHDv64NDRUWy1Q&e=
>seems to suggest USXGMII uses a fixed rate of 10.3125Gb/s. So why do
>you need to change the rate?
For USXGMII, Cadence MAC need to be correctly programmed for external serdes rate.

Regards,
Parshuram Thombare