netdev - Re: [patch net-next RFC 03/12] mlxsw: core: Add core environment module for port temperature reading

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Date:   Tue, 26 Jun 2018 20:18:21 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Vadim Pasternak <vadimp@...lanox.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "rui.zhang@...el.com" <rui.zhang@...el.com>,
        "edubezval@...il.com" <edubezval@...il.com>,
        "jiri@...nulli.us" <jiri@...nulli.us>
Subject: Re: [patch net-next RFC 03/12] mlxsw: core: Add core environment
 module for port temperature reading

> However, I have some concerns on this matter.
> Our hardware provides bulk reading of the modules temperature, means
> I can get all inputs by one hardware request, which is important optimization.
> Reading each module individually will be resulted in huge overhead and will
> require maybe some cashing of temperature inputs.  

Well, you can cache the SFP calibration values, and the 4 limit
values. To get an actually temperature you need to read 2 bytes from
the SFP module. I don't see why that would be expensive. You talk to
the firmware over PCIe right? So you have lots of bandwidth.

    Andrew