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

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Date:	Wed, 2 Sep 2015 14:09:51 +0200
From:	Arend van Spriel <arend@...adcom.com>
To:	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Ming Lei <ming.lei@...onical.com>
CC:	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>,
	"Dmitry Torokhov" <dmitry.torokhov@...il.com>,
	"joonas.lahtinen@...ux.intel.com" <joonas.lahtinen@...ux.intel.com>,
	Tom Gundersen <teg@...m.no>, Al Viro <viro@...iv.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	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 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.

That sounds good to me and learning about the async probe type. We do a 
schedule work in our module_init to avoid the probe being done in init 
context. Guess we can change that using the async probe type :-p

Regards,
Arend
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