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

[Florian Fainelli]

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