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

From: Arend Van Spriel
Date: Tue May 16 2017 - 04:42:20 EST

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 MichaÅ
>> 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.

> 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.

> [0]
> 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?