Re: Problems loading firmware using built-in drivers with kernels that use initramfs.

From: Dmitry Torokhov
Date: Wed Sep 02 2015 - 19:13:57 EST

On Wed, Sep 2, 2015 at 2:03 PM, Arend van Spriel <arend@xxxxxxxxxxxx> 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@xxxxxxxxxxxx> 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 =
>> 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.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at