linux-kernel - Re: [PATCH 1/3] ARM: dts: NSP: Enable SFP on bcm958625hr

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Message-ID: <20180827222646.GF30658@n2100.armlinux.org.uk>
Date:   Mon, 27 Aug 2018 23:26:46 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Jon Mason <jonmason@...adcom.com>,
        "maintainer:BROADCOM IPROC ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>, andrew@...n.ch
Subject: Re: [PATCH 1/3] ARM: dts: NSP: Enable SFP on bcm958625hr

On Mon, Aug 27, 2018 at 01:03:42PM -0700, Florian Fainelli wrote:
> Enable the SFP connected to port 5 of the switch and wire up all GPIOs
> to the SFP cage. Because of a hardware limitation of the i2c controller
> on the iProc SoCs which prevents large i2c (> 256 bytes) transactions to
> work, we use the i2c-gpio interface instead, which does not have that
> limitation. This allows us to read the SFP module EEPROM, which would
> not be possible otherwise since it exceeds that size during a single
> read transfer.

We shouldn't exceed 256 bytes, since 256 bytes is the "page" size
of the EEPROM.  The most that we read in one block is either
ETH_MODULE_SFF_8079_LEN or (ETH_MODULE_SFF_8472_LEN - 
ETH_MODULE_SFF_8079_LEN), both of which result in no more than 256
byte reads.

-- 
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