On Fri, Jun 26, 2020 at 06:33:55PM +0100, Adrian Pop wrote:
> >
> > Is page 03h valid for a QSFP DD? Do we add pages 10h and 11h after
> > page 03h, or instead of? How do we indicate to user space what pages
> > of data have been passed to it?
> >
> > Andrew
>
> >From QSFP-DD CMIS Rev 4.0: "In particular, support of the Lower Memory
> and of Page 00h is required for all modules, including passive copper
> cables. These pages are therefore always implemented. Additional
> support for Pages 01h, 02h and bank 0 of Pages 10h and 11h is required
> for all paged memory modules."
>
> According to the same document, page 0x03 contains "User EEPROM
> (NVRs)". Byte 142, bit 2, page 0x01 indicates if the user page 0x03
> was implemented. I did not find anything about page 0x02 (where the
> user EEPROM is stored) in the documentation for QSFP. I suppose it is
> always implemented? If we really want to have it so it is similar to
> QSFP, one could send 896 bytes (instead of 768) and just fill that
> portion with 0 in case it's not implemented. Note that this is just an
> idea, I'm not aware of best practices in cases like this.
It does seem common to only return a subset of the pages. This patch
for example. We need some clear rules to known what the kernel has
passed to user space, so we can both correctly interpret when a subset
has been passed, and also ensure all drivers are doing the same thing.
Currently we have:
* ---------- ---------- --------- ------------
* | Upper | | Upper | | Upper | | Upper |
* | Page 00h | | Page 01h | | Page 02h | | Page 03h |
* | | |(Optional)| |(Optional)| | (Optional) |
* | | | | | | | |
* | | | | | | | |
* | ID | | AST | | User | | For |
* | Fields | | Table | | EEPROM | | Cable |
* | | | | | Data | | Assemblies |
* | | | | | | | |
* | | | | | | | |
* ----------- ----------- ---------- --------------
You are saying pages 00h, 01h and 02h are mandatory for QSPF-DD. Page
03h is optional, but when present, it seems to contain what is page
02h above. Since the QSPF KAPI has it, QSPF-DD KAPI should also have
it. So i would suggest that pages 10h and 11h come after that.
If a driver wants to pass a subset, it can, but it must always trim
from the right, it cannot remove pages from the middle.
Andrew
