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

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Message-ID: <E7B1D079BA13FB44A978CC8F69C7D6A9055A1C48@SHSMSX101.ccr.corp.intel.com>
Date:	Wed, 26 Aug 2015 05:12:46 +0000
From:	"Jie, Yang" <yang.jie@...el.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Takashi Iwai <tiwai@...e.de>
CC:	"Luis R. Rodriguez" <mcgrof@...e.com>,
	"Girdwood, Liam R" <liam.r.girdwood@...el.com>,
	"joonas.lahtinen@...ux.intel.com" <joonas.lahtinen@...ux.intel.com>,
	Tom Gundersen <teg@...m.no>, Ming Lei <ming.lei@...onical.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	Kay Sievers <kay@...y.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Luis Rodriguez <mcgrof@...not-panic.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: RE: Problems loading firmware using built-in drivers with kernels
 that use initramfs.

> -----Original Message-----
> From: Dmitry Torokhov [mailto:dmitry.torokhov@...il.com]
> Sent: Wednesday, August 26, 2015 3:58 AM
> To: Takashi Iwai
> Cc: Luis R. Rodriguez; Girdwood, Liam R; Jie, Yang;
> joonas.lahtinen@...ux.intel.com; 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@...e.de> 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.

Thanks,
~Keyon

> 
> 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