Messages in this thread | | | Date | Thu, 3 Sep 2015 01:22:49 +0200 | From | "Luis R. Rodriguez" <> | Subject | Re: Problems loading firmware using built-in drivers with kernels that use initramfs. |
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On Wed, Sep 02, 2015 at 04:13:51PM -0700, Dmitry Torokhov wrote: > On Wed, Sep 2, 2015 at 2:03 PM, Arend van Spriel <arend@broadcom.com> wrote: > > On 09/02/2015 08:58 PM, Luis R. Rodriguez wrote: > >> > >> On Wed, Sep 02, 2015 at 02:13:49PM +0200, Arend van Spriel wrote: > >>> > >>> On 09/02/2015 02:09 PM, Arend van Spriel wrote: > >>>> > >>>> On 09/02/2015 03:19 AM, Luis R. Rodriguez wrote: > >>>>> > >>>>> On Mon, Aug 31, 2015 at 10:21:34PM +0800, Ming Lei wrote: > >>>>>> > >>>>>> On Sun, Aug 30, 2015 at 4:25 PM, Arend van Spriel > >>>>>> <arend@broadcom.com> wrote: > >>>>>>> > >>>>>>> Does this mean a built-in driver can not get firmware from initramfs > >>>>>>> or > >>>>>>> built in the kernel early. Seems a bit too aggressive. The problem > >>>>>>> stated in > >>>>>>> this thread is when the firmware is not on initramfs but only on the > >>>>>>> rootfs. > >>>>>> > >>>>>> > >>>>>> Yes, strictly speaking, user mode request can't be handled with defer > >>>>>> probe > >>>>>> during booting because we don't know how the user helper handles the > >>>>>> request, > >>>>> > >>>>> > >>>>> FWIW I have a strategy in mind to help us compartamentalize the user > >>>>> mode > >>>>> helper only to the dell-rbu driver, and as such phase out that code > >>>>> eventually > >>>>> completely. Its part of the goals I have with the extensible firmware > >>>>> API I've > >>>>> been proposing. > >>>>> > >>>>>> that said even checking if the firmware exists in current path doesn't > >>>>>> make sense for user mode request. > >>>>>> > >>>>>> So the patch should have used defer proble for direct load only > >>>>>> during booting. > >>>>> > >>>>> > >>>>> What exact guarantees would we be giving to callers if they follow up > >>>>> on probe > >>>>> with -EDEFER_PROBE ? I'd much prefer to try to avoid such uses in init > >>>>> / probe > >>>>> (note that unless you're using async probe since we batch both so it > >>>>> doesn't really > >>>>> matter where you place your code) all together and then for the few > >>>>> remaining > >>>>> stragglers understand the requirements and provide an interface that > >>>>> lets them > >>>>> claim their requirements and try to meets them. > >>>>> > >>>>> A grammatical hunt for drivers who call fw API on init / probe can be > >>>>> completed, although I know the hunt needs a bit more fine tuning it > >>>>> surely can > >>>>> be completed. If we don't have many callers the compexity added for > >>>>> only a > >>>>> few callers with rather loose criteria seems rather unnecessary, > >>>>> specially if > >>>>> we can change the drivers and make these driver sthe exception rather > >>>>> than > >>>>> a norm. > >>>>> > >>>>> Then as for drivers *needing* the fw at probe why not have a proper > >>>>> interface > >>>>> that does guarantee they get the requirements they ask for first ? For > >>>>> instance > >>>>> a new probe type specified by the driver could enable the core to wait > >>>>> for say > >>>>> an event and then tirgger a probe, kind of how we ended up defining > >>>>> the async > >>>>> probe type preference: > >>>>> > >>>>> static struct some_bus_driver some_driver = { > >>>>> .probe = some_probe, > >>>>> .id_table = some_id, > >>>>> .driver = { > >>>>> .name = DEVICE_NAME, > >>>>> .pm = &some_pm_ops, > >>>>> .probe_type = PROBE_PREFER_POST_FOO, > >>>>> }, > >>>>> }; > >>>>> > >>>>> Then we just don't try just hoping for completion but rather can do > >>>>> something > >>>>> about the criteria passed. > >>> > >>> > >>> So should the probe type indicate some event or should it just > >>> indicate what the driver needs, ie. .probe_type = > >>> PROBE_TYPE_NEED_FW. > >> > >> > >> Right so this is an open question. I suggested something like the above > >> since the deferred probe documentation on drivers/base/dd.c states: > >> > >> * Sometimes driver probe order matters, but the kernel doesn't always > >> have > >> * dependency information > >> > >> I'm alluding that we consider *avoiding* -EPROBE_DEFER for areas of the > >> kernel where some work can be done to not only list the dependency > >> the information from the driver but also we know we can get it from > >> the kernel. In this case I do believe we could not only express the > >> requirement but also wait for it in the kernel. Before we do that > >> though I think it'd be good to do a grammar hunt to determine exactly > >> how popular all this fw on probe needed really is. > > > > > > Ok. So some background why we need it in brcm80211 drivers. So as a wireless > > network device driver the answer we got when asking for an event to load > > firware is upon IF_UP for a registered net device. Because we try to do > > things smart we query the firmware running on the device for capabilities > > before we can register the net device hence we request the firmware during > > probe. This may be specific to wireless drivers (Intel has same approach if > > not mistaken) but I suspect there may be more. > > We have the same issue with input devices: before we can register one > we need to set their capabilities and to know their capabilities we > quite often need to load their firmware/config and query the device.
Should Arend's driver use async probe then?
IMHO its just as hacky as using -EPROBE_DEFER too, but its at least preemptively hacky. Sadly I can't think of clear and clever way for the kernel to know when firmware will be ready either... Would userspace know? Should the kernel learn this from userspace ?
For instance, if init is going to use initramfs it can pivot_root() and later send us a smoke signal when done, and it it doesn't it can also send us a smoke signal. In the absence of such a hint being implemented I suppose -EPROBE_DEFER, async probe or a notifier on pivot_root() is best effort we can do, but again *eh*.
Luis
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