On 19 June 2018 at 17:14, Yang Zhang yang.zhang@96boards.org wrote:
On 18 June 2018 at 14:22, Ard Biesheuvel ard.biesheuvel@linaro.org wrote:
On 18 June 2018 at 14:21, Arnd Bergmann arnd@arndb.de wrote:
On Mon, Jun 18, 2018 at 9:45 AM, Linus Walleij linus.walleij@linaro.org wrote:
This is a proposal for how to handle the non-discoverable 96boards plug-in expansion boards called "mezzanines" in the Linux kernel. It is a working RFC series meant for discussion at the moment.
The RFC was done on the brand new Ultra96 board from Xilinx with a Secure96 mezzanine expansion board. The main part is in patch 4, the rest is enabling and examples.
The code can be obtained from here:
https://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-integrator.git/...
You can for example probably augment the DTS file for any upstream-supported 96board and get the Secure96 going with it with minor efforts.
Hi Linus,
Thanks for your work on solving this long-standing problem. I've just read through your patches briefly and have a few thoughts:
I really like the idea of having C code deal with the mezzanine connector itself, acting as an intermediate to tie a number of boards to a number of add-on cards, this seems much simpler than trying to do everything with overlays or one of the other more generic mechanisms.
I don't like the idea of having the bus driver contain a list of
possible add-ons, this seems to go against our usual driver model. What I think we want instead is to make the connector itself a proper bus_type, to allow drivers to register against it as loadable modules, and devices (maybe limited to one device) being created as probed from DT or some other method as you describe.
- You export symbols in the mezzanine_* namespace, which I think is a bit too generic and should perhaps contain something related to 96boards in its name to make it less ambiguous. I suspect we would add a number of further connectors for hats, capes, lures etc, which could all be described as mezzanines. One open question is how we structure the commonality between the various connectors, but we can defer that until we have more than one or two of them.
Hello all,
We should also consider firmware use of the mezzanines. For instance, the Secure96 has a RNG which UEFI may want to use so the early boot code can access is for KASLR. It also has a TPM, which should not be reset/reinitialized/etc by the OS if we want to make meaningful use of it.
Also, given that we can (and do) already describe topologies involving mezzanines by ignoring the connector altogether (which is not entirely unreasonable given the fact that we [as Linaro/96boards] dropped the ball on this one and did not mandate discoverability for mezzanines).
The design guideline has been reviewed by many inside/outside linaro through the mezzanine@lists.96boards.org and 96b-spec-sig 96b-spec-sig@96boards.org published as recommended/strongly recommended item from day one. 'dropping the ball' is a strong conclusion.
Apologies for using a term that you seem to take issue with. Are you saying the spec currently recommends it?