Re: [PATCH 3/5] firmware: revamp firmware documentation

Luis R. Rodriguez
2016-12-16T09:09:44Z

On Tue, Dec 13, 2016 at 08:26:41AM +0100, Rafał Miłecki wrote:
> On 12/13/2016 04:08 AM, Luis R. Rodriguez wrote:
> > Understanding this code is getting out of control without any
> > notes. Give the firmware_class driver a much needed documentation love,
> > and while at it convert it to the new sphinx documentation format.
>
> It does help to understand the class/API, thank you!

Glad it is helping!

> > +Even if you have these needs there are a few reasons why you may not be
> > +able to make use of built-in firmware:
> > +
> > +* Legalese - firmware is non-GPL compatible
> > +* Some firmware may be optional
> > +* Firmware upgrades are possible, therefore a new firmware would implicate
> > + a complete firmware rebuild.
>
> Could it be you meant "kernel rebuild" or "vmlinux rebuild" here?

Heh, yes... thanks, fixed!

> > diff --git a/Documentation/driver-api/firmware/fallback-mechanisms.rst b/Documentation/driver-api/firmware/fallback-mechanisms.rst
> > new file mode 100644
> > index 000000000000..edce1d76ce29
> > --- /dev/null
> > +++ b/Documentation/driver-api/firmware/fallback-mechanisms.rst
> > @@ -0,0 +1,195 @@
> > +===================
> > +Fallback mechanisms
> > +===================
> > +
> > +A fallback mechanism is supported to allow to overcome failures to do a direct
> > +filesystem lookup on the root filesystem or when the firmware simply cannot be
> > +installed for practical reasons on the root filesystem. The kernel
> > +configuration options related to supporting the firmware fallback mechanism are:
> > +
> > + * CONFIG_FW_LOADER_USER_HELPER: enables building the firmware fallback
> > + mechanism. Most distributions enable this option today. If enabled but
> > + CONFIG_FW_LOADER_USER_HELPER_FALLBACK is disabled, only the custom fallback
> > + mechanism is available and for the request_firmware_nowait() call.
> > + * CONFIG_FW_LOADER_USER_HELPER_FALLBACK: force enables each request to
> > + enable the kobject uevent fallback mechanism on all firmare API calls
> > + except request_firmware_direct(). Most distributions disable this option
> > + today. The call request_firmware_nowait() allows for one alternative
> > + fallback mechanism: if this kconfig option is enabled and your second
> > + argument to request_firmware_nowait(), uevent, is set to false you are
> > + informing the kernel that you have a custom fallback mechanism and it will
> > + manually load the firmware. Read below for more details.
>
> Yeah, it really asks for API simplification ;)

So up next once this is done is the new revamp with an extensible firmware API.

Luis