Re: loading firmware while usermodehelper disabled.

From: Marek Vasut
Date: Sat Dec 31 2011 - 13:39:29 EST

> On Fri, Dec 30, 2011 at 3:54 PM, Dave Jones <davej@xxxxxxxxxx> wrote:
> > We're getting a bunch of reports against Fedora 16
> > (still using 3.1) which look like some drivers are trying to
> > load firmware on resume from suspend, while usermodehelper
> > is disabled.
> Ok, buggy drivers. You *must*not* load firmware in your resume path,
> since there is no actual guarantee that any particular device will be
> resumed after the disk that contains the firmware images.
> So it's very simple: drivers that load firmware at resume time are
> buggy. No ifs, buts, or maybes about it.
> > Here are some example traces:
> >
> >
> It's isight_firmware_load(), in the isight_firmware driver. The driver
> doesn't actually do anything but load the firmware, and is apparently
> not very good at that either.
> It should either fake a disconnect and reconnect of the device (and
> let the reconnect then load the firmware through udev or something) or
> it should just save the firmware image in memory from the original
> load, and make the resume just re-initialize it - not load it.


maybe we should implement such thing into the firmware loader itself? Allow it
-- for example via some node in /dev -- to force loading firmware into some
buffer in kernel just before suspend so it'll certainly be readily available at
resume time?


> It's also possible that it could be considered a USB layer bug, and
> the USB layer should just not rebind the devices directly in the
> resume function, but do it somehow later. HOWEVER, that would only
> work for "random" USB devices that aren't in use by user space (like
> disks etc might be). So I think that in general the real solution is
> always just "make sure that the firmware is in memory before the
> suspend even happens".
> Greg - has the USB resume logic been changed lately?
> Matthew? Any comments about that particular driver?
> >
> Same issue, different driver. Again, it's USB, and it's possible that
> USB just makes it really hard to do this correctly (ie the "save
> firmware image across suspend so that you don't have to load it at
> resume time").
> It's also possible that we should blame the firmware code, which is
> expressly written to encourage these kinds of bugs. It may be that i
> tshould be the firmware code that has a "get_firmware()" +
> "put_firmware()" model, and it should cache the firmware explicitly if
> the config supports suspend, so that a firmware read at resume time
> would actually work. The whole "request_firmware()" interface really
> is very prone to these kinds of bugs.
> But it's possible this could be fixed at the driver level by doing the
> caching there.
> In this case it's the rtl8192cu driver, so Larry, Chaoming, John etc
> added to the cc for that one.
> > This possibly sounds like the problem that
> > caca9510ff4e5d842c0589110243d60927836222 was trying to fix, but that
> > patch is present in the kernels
> > being reported.
> No, caca9510ff4e is only for the case where you actually compile the
> firmware *into* the kernel, so it's part of the kernel image. That's
> useful mainly for avoiding modules and initrd images, thus allowing
> things like having root directly on a disk that needs firmware to be
> loaded. Quite unusual, and it doesn't really work all that well.
> Oh, and some people use it for the Radeon firmware with the radeon DRM
> code built it.
> It really does need to be fixed at a driver level (possibly with the
> help of firmware/usb support infrastructure).
> Linus
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