netdev - Re: [PATCH net-next v5 1/5] net: sfp: add SFP

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Message-ID: <20210114145953.GS1551@shell.armlinux.org.uk>
Date:   Thu, 14 Jan 2021 14:59:53 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Marek Behún <kabel@...nel.org>
Cc:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net,
        pali@...nel.org
Subject: Re: [PATCH net-next v5 1/5] net: sfp: add SFP_PASSWORD address

On Thu, Jan 14, 2021 at 05:43:27AM +0100, Marek Behún wrote:
> Add SFP_PASSWORD = 0x7b to the diagnostics enumerator. This address is
> described in SFF-8436 and SFF-8636.

However, as I mentioned previously, these are not relevant for SFPs,
but are for QSFPs, and QSFPs have a totally different layout.

The data structure for this enum is described by SFF-8472, and it lists

	Vendor Specific Locations [Address A2h, Bytes 120-126]

This is what the SFP_VSL definition covers.

SFF-8436 defines the layout for "QSFP+ 10 Gbs 4X PLUGGABLE TRANSCEIVER":

                            Table 17 - Lower Memory Map (A0h)
       Address       Description         Type         Passive Copper,     Optical
                                                      Active Copper,      Module                                                      Active Optical
       0             Identifier (1       Read-Only    R                   R
                     Byte)
       1-2           Status (2 Bytes)     Read-Only    See Table 18
       3-21          Interrupt Flags      Read-Only    See Tables 19-21
                     (19 Bytes)
...
       123-126       Password Entry       Read/Write   O                  O
                     Area (optional) 4
                     Bytes
       127           Page Select Byte     Read/Write   R                  R

So, SFF-8436 is not relevant - not only is it for a different address
but the whole format is different.

SFF-8636 is "Specification for Management Interface for Cabled
Environments" and defines:

                             2-Wire Serial Address 1010000x
                                     Lower Page 00h
                            0 Identifier
                        1- 2 Status
                        3- 21 Interrupt Flags
...
                      123-126 Password Entry Area (Optional)
                      127     Page Select Byte

So again, SFF-8636 is not relevant for the same reasons as SFF-8436.

We're left with SFF-8472, which mentions no password entry area, but
leaves the area from 120-127 open as "vendor specific", so I don't
think it is appropriate to start adding vendor specific definitions as
if they were generic to sfp.h

I would instead suggest defining this inside mdio-i2c.c as

#define ROLLERBALL_PASSWORD	(SFP_VSL + 3)

rather than trying to make this appear generic.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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