Re: [PATCH v2] firmware loader: allow disabling of udev as firmware loader

[Takashi Iwai <tiwai@suse.de>]

At Thu, 5 Jun 2014 22:54:33 +0800,
Ming Lei wrote:
> 
> On Thu, Jun 5, 2014 at 10:32 PM, Tom Gundersen <teg@jklm.no> wrote:
> > On Thu, Jun 5, 2014 at 4:24 PM, Ming Lei <ming.lei@canonical.com> wrote:
> >> On Thu, Jun 5, 2014 at 10:05 PM, Takashi Iwai <tiwai@suse.de> wrote:
> >>> At Thu, 5 Jun 2014 21:59:52 +0800,
> >>> Ming Lei wrote:
> >>>>
> >>>> On Thu, Jun 5, 2014 at 9:47 PM, Takashi Iwai <tiwai@suse.de> wrote:
> >>>> > At Thu, 5 Jun 2014 21:31:56 +0800,
> >>>> > Ming Lei wrote:
> >>>> >>
> >>>> >> On Thu, Jun 5, 2014 at 8:25 PM, Tom Gundersen <teg@jklm.no> wrote:
> >>>> >> >
> >>>> >> > On 5 Jun 2014 14:18, "Ming Lei" <ming.lei@canonical.com> wrote:
> >>>> >> >>
> >>>> >> >> On Wed, Jun 4, 2014 at 11:48 PM, Takashi Iwai <tiwai@suse.de> wrote:
> >>>> >> >> > [The patch was originally proposed by Tom Gundersen, and rewritten
> >>>> >> >> >  afterwards by me; most of changelogs below borrowed from Tom's
> >>>> >> >> >  original patch -- tiwai]
> >>>> >> >> >
> >>>> >> >> > Currently (at least) the dell-rbu driver selects FW_LOADER_USER_HELPER,
> >>>> >> >> > which means that distros can't really stop loading firmware through
> >>>> >> >> > udev without breaking other users (though some have).
> >>>> >> >> >
> >>>> >> >> > Ideally we would remove/disable the udev firmware helper in both the
> >>>> >> >> > kernel and in udev, but if we were to disable it in udev and not the
> >>>> >> >> > kernel, the result would be (seemingly) hung kernels as no one would
> >>>> >> >> > be around to cancel firmware requests.
> >>>> >> >> >
> >>>> >> >> > This patch allows udev firmware loading to be disabled while still
> >>>> >> >> > allowing non-udev firmware loading, as done by the dell-rbu driver, to
> >>>> >> >> > continue working. This is achieved by only using the fallback
> >>>> >> >> > mechanism when the uevent is suppressed.
> >>>> >> >> >
> >>>> >> >> > The patch renames the user-selectable Kconfig from FW_LOADER_USER_HELPER
> >>>> >> >> > to FW_LOADER_USER_HELPER_FALLBACK, and the former is reverse-selected
> >>>> >> >> > by the latter or the drivers that need userhelper like dell-rbu.
> >>>> >> >> >
> >>>> >> >> > Also, the "default y" is removed together with this change, since it's
> >>>> >> >> > been deprecated in udev upstream, thus rather better to disable it
> >>>> >> >> > nowadays.
> >>>> >> >> >
> >>>> >> >> > Tested with
> >>>> >> >> >     FW_LOADER_USER_HELPER=n
> >>>> >> >> >     LATTICE_ECP3_CONFIG=y
> >>>> >> >> >     DELL_RBU=y
> >>>> >> >> > and udev without the firmware loading support, but I don't have the
> >>>> >> >> > hardware to test the lattice/dell drivers, so additional testing would
> >>>> >> >> > be appreciated.
> >>>> >> >> >
> >>>> >> >> > Reviewed-by: Tom Gundersen <teg@jklm.no>
> >>>> >> >> > Cc: Ming Lei <ming.lei@canonical.com>
> >>>> >> >> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> >>>> >> >> > Cc: Abhay Salunke <Abhay_Salunke@dell.com>
> >>>> >> >> > Cc: Stefan Roese <sr@denx.de>
> >>>> >> >> > Cc: Arnd Bergmann <arnd@arndb.de>
> >>>> >> >> > Cc: Kay Sievers <kay@vrfy.org>
> >>>> >> >> > Signed-off-by: Takashi Iwai <tiwai@suse.de>
> >>>> >> >> > ---
> >>>> >> >> >  drivers/base/Kconfig          | 10 ++++++++--
> >>>> >> >> >  drivers/base/firmware_class.c | 15 ++++++++++-----
> >>>> >> >> >  include/linux/firmware.h      |  2 +-
> >>>> >> >> >  3 files changed, 19 insertions(+), 8 deletions(-)
> >>>> >> >> >
> >>>> >> >> > diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> >>>> >> >> > index 8fa8deab6449..d0bb32e4c416 100644
> >>>> >> >> > --- a/drivers/base/Kconfig
> >>>> >> >> > +++ b/drivers/base/Kconfig
> >>>> >> >> > @@ -144,15 +144,21 @@ config EXTRA_FIRMWARE_DIR
> >>>> >> >> >           some other directory containing the firmware files.
> >>>> >> >> >
> >>>> >> >> >  config FW_LOADER_USER_HELPER
> >>>> >> >> > +       bool
> >>>> >> >> > +
> >>>> >> >> > +config FW_LOADER_USER_HELPER_FALLBACK
> >>>> >> >> >         bool "Fallback user-helper invocation for firmware loading"
> >>>> >> >> >         depends on FW_LOADER
> >>>> >> >> > -       default y
> >>>> >> >> > +       select FW_LOADER_USER_HELPER
> >>>> >> >> >         help
> >>>> >> >> >           This option enables / disables the invocation of user-helper
> >>>> >> >> >           (e.g. udev) for loading firmware files as a fallback after the
> >>>> >> >> >           direct file loading in kernel fails.  The user-mode helper is
> >>>> >> >> >           no longer required unless you have a special firmware file
> >>>> >> >> > that
> >>>> >> >> > -         resides in a non-standard path.
> >>>> >> >> > +         resides in a non-standard path. Moreover, the udev support has
> >>>> >> >> > +         been deprecated upstream.
> >>>> >> >> > +
> >>>> >> >> > +         If you are unsure about this, say N here.
> >>>> >> >>
> >>>> >> >> It may be safer to say Y here for fallback if not sure.
> >>>> >> >
> >>>> >> > Saying Y here will be actively harmful if the firmware loader is disabled in
> >>>> >> > udev (which I guess most distros will do as soon as they can), so I think we
> >>>> >>
> >>>> >> If fallback is triggered, it means that the firmware can't be found
> >>>> >> in default direct rootfs path, so it is better to continue to look for it
> >>>> >> from userspace.
> >>>> >>
> >>>> >> Also it won't a big problem for hanging the request user context
> >>>> >> for some while(60sec at default) if udev is disabled, will it?
> >>>> >>
> >>>> >> BTW, are you sure most distros will do that in the near future?
> >>>> >>
> >>>> >> > should advice people to say N unless they really know what they are doing
> >>>> >> > and that their userspace can cope with it.
> >>>> >>
> >>>> >> That is why I suggest to say Y if someone isn't sure.
> >>>> >
> >>>> > For the time being, having default this Y causes more troubles.
> >>>>
> >>>> I am wondering why default Y may cause more troubles, as we
> >>>> know, it has been default Y for long long time.
> >>>
> >>> More trouble = more bug reports.  At least, a handful distros suffer.
> >>> I don't know the situation with Ubuntu, though.
> >>
> >> Looks recently not see related report, :-)
> >
> > Ubuntu currently enables the firmware loader in both the kernel and in
> > udev, so would not yet have a problem here at the moment. However, I
> > spoke with Martin Pitt and he told me that both Debian and Ubuntu
> > would like to switch this off in udev once it is possible (i.e., once
> > this patch has been merged I guess). Fedora already did, and speaking
> > for Arch we definitely would like to do the same. I did not check with
> > other distros, but I'm pretty sure "everyone" will disable this in
> > udev by the next cycle. At which point having it enabled in the kernel
> > will cause real problems and bug reports.
> 
> That won't cover the case of old distributions with new kernel, do
> you want to break/confuse these users?

Why it breaks?  They can just select it.

> > For distro kernels that's not a problem, as they know what to do, but
> > I guess for random kernel users we should give them the correct
> > recommendation.
> 
> Also I remember that android users put firmware under their
> special path.

And, they are sure what Kconfig options to take.

> >>>> It only falls back if the request fw is _not_ found from direct loading,
> >>>> so it is reasonable to try to continue to look for it from user space.
> >>
> >>> Some drivers fall back to different firmware (e.g. different revision
> >>> suffix) if the requested file isn't found.  So, this happens in
> >>> reality.
> >>
> >> So do you think the fallback is better or worse? For CPU microcode
> >> case, maybe it is fine, but for other devices, maybe it is better to
> >> get a firmware for working at least.
> >
> > What usecase do you have in mind here? For people using stock udev,
> > enabling the fallback will not give any benefit, but it will soon
> 
> Again, we have old distributions, also it should make sense to fall back
> to userspace for non-exist firmwares under default path.
> 
> > start giving real problems...
> 
> If there isn't firmwares at default path for devices, the device may
> not work, and that is the real problem.

Ming, we're discussing about the help text for people who aren't sure
what to select.  Which chance would you bet as such a target?  A
newbie, or a bearded techy sticking with old distros?

For people who are using the old distros *and* with non-standard
firmware paths, they must be sure what they're doing and what they
must select.


thanks,

Takashi