Re: [RFC][PATCH -mm 3/3] PM: Disable _request_firmware before hibernation/suspend

Michael-Luke Jones
2007-05-28T12:26:37Z

On 28 May 2007, at 12:51, Kay Sievers wrote:

> Either the whole idea of userspace firmware-loading should be
> considered
> as a problem impossible to do right because of its unsolvable side
> effects. Or at least releasing loaded firmware should be the exception
> for drivers which can be sure, that the firmware is not needed in
> situations we try to work around here.

I don't believe that it is impossible. What is needed is some
thought, and maybe a loose spec.

We need to think about safe ways of solving a simple problem: what to
do when userspace is unable to respond to a kernel uevent request. We
now have a timeout, whether it be handled synchronously or in the
background. I don't think either solution is good enough.

[RFC] Possible Plan:

1) request_firmware() should stick around unmodified but be marked
__deprecated.

2) request_firmware_nowait() as it stands should probably be removed.
After all, it only has 2 in-kernel users at the moment.

3) uevent interface should be notified when userspace handlers are /
are not available so that events can be queued to be handled when
userspace does turn up and re-register a hotplug event handler.

4) request_firmware_async() introduced: asynchronous firmware loading
interface built on basis of 3, such that problems at early boot and
suspend / resume are avoided. Also request_firmware_async() taught to
retain firmware in memory by default such that subsequent calls do
not require a call to userspace if userspace is unavailable.

6) Documentation on correct firmware loading behaviour for driver
authors written, together with migration notes for existing users of
request_firmware().

7) Existing uses of request_firmware() converted.

*Grumble ahead*
Unfortunately, I don't properly understand the uevent interface, so
some of the above may be inaccurate. This is *not* my fault as there
is no decent documentation (and btw, telling me to write the
documentation is not the answer to that problem).

Michael-Luke