netdev - Re: [PATCH] net: sfp: read eeprom in maximum 16 byte increments

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Date:   Mon, 3 Jun 2019 21:52:47 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Russell King <rmk+kernel@...linux.org.uk>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: sfp: read eeprom in maximum 16 byte increments

On Sun, Jun 02, 2019 at 03:13:00PM +0100, Russell King wrote:
> Some SFP modules do not like reads longer than 16 bytes, so read the
> EEPROM in chunks of 16 bytes at a time.  This behaviour is not specified
> in the SFP MSAs, which specifies:
> 
>  "The serial interface uses the 2-wire serial CMOS E2PROM protocol
>   defined for the ATMEL AT24C01A/02/04 family of components."
> 
> and
> 
>  "As long as the SFP+ receives an acknowledge, it shall serially clock
>   out sequential data words. The sequence is terminated when the host
>   responds with a NACK and a STOP instead of an acknowledge."
> 
> We must avoid breaking a read across a 16-bit quantity in the diagnostic
> page, thankfully all 16-bit quantities in that page are naturally
> aligned.
> 
> Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew