RE: Problems loading firmware using built-in drivers with kernels that use initramfs.

From: Jie, Yang
Date: Wed Aug 26 2015 - 01:13:06 EST

> -----Original Message-----
> From: Dmitry Torokhov [mailto:dmitry.torokhov@xxxxxxxxx]
> Sent: Wednesday, August 26, 2015 3:58 AM
> To: Takashi Iwai
> Cc: Luis R. Rodriguez; Girdwood, Liam R; Jie, Yang;
> joonas.lahtinen@xxxxxxxxxxxxxxx; Tom Gundersen; Ming Lei; Al Viro; Greg
> Kroah-Hartman; Kay Sievers; Linus Torvalds; David Woodhouse; Luis
> Rodriguez; lkml
> Subject: Re: Problems loading firmware using built-in drivers with kernels
> that use initramfs.
> On Tue, Aug 25, 2015 at 12:46 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> > On Tue, 25 Aug 2015 21:34:08 +0200,
> > Luis R. Rodriguez wrote:
> >>
> >> On Tue, Aug 25, 2015 at 10:17:00AM +0100, David Woodhouse wrote:
> >> > Luis, did you tell me the other day that you made the kernel get
> >> > firmware directly from the file system? This regression would be yours
> then?
> >>
> >> I didn't implement that, Linus did in 2012 (see commit abb139e75c2c
> >> titled
> >> "firmware: teach the kernel to load firmware files directly from the
> >> filesystem"). But we used to fallback to a userspace helper when the
> >> fw was not present and then Takashi made this optional via commit
> >> 7b1269f778782d titled "firmware: Make user-mode helper optional".
> >> Takashi noted in the Kconfig "The user-mode helper is no longer
> >> required unless you have a special firmware file that resides in a
> >> non-standard path". It was not clarified why that's true though, or
> >> what you'd need to do to ensure that the fw would be available. It
> >> would be good for us to elaborate on that.
> >
> > The recent udev already dropped the firmware loading feature.
> Note that even when we had udev helper to load the firmware it was not
> always reliable depending on the exact point where we requested firmware.
> If request happened in probe() path before we mounted root fs then we'd
> never get it loaded because we'd be waiting for devices settle before
> mounting rootfs.

For request in probe(), is it possible to use request_firmware_nowait() to
wait rootfs mounted or timeout in another thread?

It looks usermodehelper_disabled is 0(at probe()) at this case then no waiting occurs
here in our testing.


> Either build firmware in the kernel or ramdisk (so it is always available), or
> make sure request_firmware() calls are not in driver's
> probe() paths.
> Thanks.
> --
> Dmitry