Re: [PATCH 2/6] wl1251: Use request_firmware_prefer_user() for loading NVS calibration data

["Luis R. Rodriguez" <mcgrof@kernel.org>]

On Tue, May 16, 2017 at 10:41:08AM +0200, Arend Van Spriel wrote:
> On 16-5-2017 1:13, Luis R. Rodriguez wrote:
> > On Fri, May 12, 2017 at 11:02:26PM +0200, Arend Van Spriel wrote:
> >> try again.. replacing email address from Michał
> >> On 12-5-2017 22:55, Arend Van Spriel wrote:
> >>> Let me explain the idea to refresh your memory (and mine). It started
> >>> when we were working on adding driver support for OpenWrt in brcmfmac.
> >>> The driver requests for firmware calibration data, but on routers it is
> >>> stored in flash. So after failing on the firmware request we now call a
> >>> platform specific API. That was my itch, but it was not bad enough to go
> >>> and scratch. Now for N900 case there is a similar scenario alhtough it
> >>> has additional requirement to go to user-space due to need to use a
> >>> proprietary library to obtain the NVS calibration data. My thought: Why
> >>> should firmware_class care?
> > 
> > Agreed.
> > 
> >>> So the idea is that firmware_class provides
> >>> a registry for modules that can produce a certain firmware "file". Those
> >>> modules can do whatever is needed. If they need to use umh so be it.
> >>> They would only register themselves with firmware_class on platforms
> >>> that need them. It would basically be replacing the fallback mechanism
> >>> and only be effective on certain platforms.
> > 
> > Sure, so it sounds like the work that Daniel Wagner and Tom Gundersen worked
> > [0] on which provides a firmwared with two modes: best-effort, and final-mode,
> > would address what you are looking for but without requiring any upstream
> > changes, *and* it also helps solve the rootfs race remote-proc folks had
> > concerns over.
> > 
> > The other added gain over this solution is if folks need their own proprietary
> > concoction they can just fork firmwared and have that do whatever it needs
> > for the specific device on the specific rootfs. That is, firmwared can be the
> > upstream solution if folks need it, but if folks need something custom they can
> > just mimic the implementation: best-effort, and and final-mode.
> > 
> > Yet another added gain over this solution we can do *not* support the
> > custom fallback mechanism as its not needed, the udev event should suffice
> > to let userspace do what it needs.
> > 
> > Lastly, if we did not want to deal with timeouts for the way the driver data
> > API implements it I think we might be able to do away with them for for async
> > requests if we assume there will be a daemon that spawns in final-mode eventually,
> > and since it *knows* when the rootfs is ready it should be able to do a final
> > lookup, if it returns -ENOENT; then indeed we know we can give up. Now, perhaps
> > how and if we want to deal with timeouts when using the driver data API for
> > the fallback mechanism is worth considering given it does not have a fallback
> > mechanism support yet. If we *add* them it would seem this would also put an
> > implicit race against userspace finishing initialization and running firmwared
> > in final-mode.
> 
> Just to be clear. When you are saying "rootfs" in this story, you mean
> any (mounted) file-system which may hold the firmware. At least that was
> one of the arguments. In kernel space we can not know how the system is
> setup in terms of mount points, let alone on which mounted file-system
> the firmware resides.

Right, wherever the hell that thing is on, which could be on a crypic fuse
drive waiting for some bits to be decrypted from Elon Musk on a spaceship on his
way to Mars, and only userspace knows how to decrypt this thing through some
evil proprietary thing, way way after a full bootup.

> > Johannes, do you recall the corner cases we spoke about regarding timeouts?
> > Does this match what we spoke about?
> > 
> >>> Let me know if this idea is still of interest and I will rebase what I
> >>> have for an RFC round.
> > 
> > Since no upstream delta is needed for firmwared I'd like to first encourage
> > evaluating the above. While distributions don't carry it yet that may be seen as
> > an issue but since what we are looking for are corner cases, only folks needing
> > to deploy a specific solution would need it or a custom proprietary solution.
> 
> Ok. I will go try and run firmwared in OpenWrt on a router platform.
> Have to steal one from a colleague :-p Will study firmwared.

The finale-mode is the trick.

> > [0] https://github.com/teg/firmwared.git
> > 
> > PS.
> > 
> > Note that firmware signing will require an additional file, the detached
> > signature. The driver data API does not currently support the fallback
> > mechanism so we would not have to worry about that yet but once we add
> > fallback support we'd need to consider this.
> 
> Do you have references to the firmware signing design. Is the idea to
> have one signature and all "firmware files" need to be signed with it?

Nope, I'm afraid a lot has been discussed so best we can do is wait.

 Luis