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

[Takashi Iwai]

On Wed, 26 Aug 2015 07:12:46 +0200,
Jie, Yang wrote:
> 
> > -----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.

It's possible -- and even with the normal request_firmware(), in
theory.  The missing piece is that you need to inform the helper to
retry the f/w loading.  Currently the direct f/w loader assumes that
the file is there and returns error if not present.

If we implement a retry, another question is how to trigger it,
i.e. how the helper can know when a fs is mounted a new file is
present.


Takashi
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