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

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Message-ID: <6d6e6c18-c713-7d7d-a332-da73cca84cbe@gmail.com>
Date:   Mon, 27 Aug 2018 15:36:50 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>,
        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 08/27/2018 03:26 PM, Russell King - ARM Linux wrote:
> 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.

You are right, I got things mixed up here, the controller's limitation
is actually 63 bytes per transfer, I will be rewording the commit
message accordingly.
-- 
Florian