Re: [PATCH net-next] ethtool: Macro definition for SFF-8436/8636 Memory map max sizes

On Sat, Jun 11, 2016 at 3:51 PM, David Miller [off-list ref] wrote:

From: vidya@cumulusnetworks.com
Date: Mon,  6 Jun 2016 22:55:26 -0700

quoted

From: Vidya Sagar Ravipati <redacted>

This patch provides macro definitions for maximum possible
memory map size of QSFP+/QSFP28 EEPROMs as per SFF-8436/SFF-8636

According to SFF-8436/SFF-8636 specs, the common memory map for
managing external cable interfaces is arranged into a single
lower page address space of 128 bytes and multiple upper address pages
of 128 bytes each. The total size of memory map is up to 5 128 byte pages
defined by a "pages valid" register and switched via a "page select"
register for "optional pages". Memory of 256 bytes can be memory mapped
at a time and QSFP+/QSFP28  drivers can export upto 5*128 bytes of
eeprom dump.

QSFP+/QSFP28 Memory layout
           2-Wire Serial Address: 1010000x
           Lower Page 00h (128 bytes)
           ======================
           |Page Select Byte(127)|
           ======================
                    |
                    V
       ----------------------------------------
      |             |            |             |
      V             V            V             V
   ----------   ----------   ---------    ------------
  | Upper    | | Upper    | | Upper    | | Upper      |
  | Page 00h | | Page 01h | | Page 02h | | Page 03h   |
  |          | |(Optional)| |(Optional)| | (Optional) |
  |    ID    | |   AST    | |  User    | |  For       |
  |  Fields  | |  Table   | | EEPROM   | |  Cable     |
  -----------  -----------   ----------  --------------

Signed-off-by: Vidya Sagar Ravipati <redacted>

Why do we need these values in the header file at all?

As part of ethtool application, application is requesting  the drivers
to provide the supported eeprom size to allocate memory buffer for
getting complete dump.

In case of QSFP+/QSFP28, the size can be either 256 or 640 bytes(when
optional pages are supported) and it would be good to have same macros
across ethtool application and ethernet drivers for providing
eeprom_length field in  ETHTOOL_GMODULEINFO ioctl .

The application can probe the size by repeated eeprom calls, increasing
the buffer size each time as needed until success.