Re: [RFC] ath10k: silence firmware file probing warnings

["Luis R. Rodriguez" <mcgrof@kernel.org>]

On Fri, Jul 22, 2016 at 08:51:36AM -0400, Prarit Bhargava wrote:
> On 07/22/2016 08:21 AM, Arend Van Spriel wrote:
> >> Another option to solve to problem would be stop requesting not
> >> available publicly firmware. However, I assume some drivers would
> >> like to preserve that option.
> > 
> > Actually, this is not the case with brcmfmac. We do need a firmware
> > file, ie. brcm/brcmfmac4356-pcie.bin, and also request for a nvram file,
> > ie. brcm/brcmfmac4356-pcie.txt. The latter is optional and the device
> > works fine without it.
> > 
> > What is still unclear to me is when request_firmware_direct() would fail
> > and in what circumstances the udev helper is a valid callback. Can you
> > explain such a scenario. Another question I have is what the reasons are
> > behind the 60 seconds timeout.
> 
> request_firmware_direct() will fail when the specified FW file is not present.
> This is different from request_firmware() which implements a usermode helper to
> potentially download firmware, or unpack a firmware image.
> 
> Re: 60 second timeout ... The 60 second timeout with request_firmware() is
> completely arbitrary.  There is no way for udev to signal back to the kernel
> that userspace helper has not completed its actions, so the kernel has a 60 dead
> man timer-ish delay.

Lets call it what it was: the 60 second timeout thing was simply a mistake.
Its no longer 60 seconds anyway, and in fact its accepted a dreaded issue.
What *we* should be doing is thinking about proper long term architecture now.
Async probe was one solution to some issues, a new flexible firmware API
that avoids the usermode helper 100% is another.

Distros stuck with the fallback option should review their strategies,
either disabling the fallback option, upgrade systemd, or use alternative
solutions (opensuse has a good one).

> >>>> However I wonder if changing that will not broke the case when
> >>>> driver is build-in in the kernel and f/w is not yet available when
> >>>> driver start to initialize. Or maybe nowadays this is not the case
> >>>> any longer, i.e. the MODULE_FIRMWARE macros assure proper f/w 
> >>>> images are build-in in the kernel or copied to initramfs?
> >>>
> >>> That is a nice idea, but I have not seen any change in that area. Could
> >>> have missed it.
> >>
> >> I believe this is how the things are already done, IOW switching to
> >> request_firmware_direct() in the driver should be no harm.
> > 
> > Ok. What are the consequences when:
> > - driver is built-in.
> > - driver+firmware present on initramfs.
> > - driver on initramfs, firmware only present on rootfs.
> > - driver+firmware only on rootfs.
> > 
> > I assume the third one would be considered a configuration issue.
> 
> I think your question here can be answered by reading drivers/base/Kconfig:88,
> and reading about those 4 config options.

No, this documentation is terrible, I've posted some patches to help with this
mess.

> I could paraphrase it butI think the
> Kconfig notes are better than I could explain it.  Note that this is how things
> currently work with request_firmware_nowait().  IIRC request_firmware_nowait()
> is just an asynchronous version of request_firmware().

... its a mess.

  Luis