Date:	Wed, 2 Sep 2015 16:13:51 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Arend van Spriel <arend@...adcom.com>
Cc:	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ming Lei <ming.lei@...onical.com>,
	Takashi Iwai <tiwai@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
	"Jie, Yang" <yang.jie@...el.com>,
	"joonas.lahtinen@...ux.intel.com" <joonas.lahtinen@...ux.intel.com>,
	Tom Gundersen <teg@...m.no>, Al Viro <viro@...iv.linux.org.uk>,
	Kay Sievers <kay@...y.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Luis Rodriguez <mcgrof@...not-panic.com>,
	lkml <linux-kernel@...r.kernel.org>,
	yalin wang <yalin.wang2010@...il.com>
Subject: Re: Problems loading firmware using built-in drivers with kernels
 that use initramfs.

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

Thanks.

-- 
Dmitry
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