linux-kernel - Re: [RFC v0 7/8] Input: ims-pcu: use firmware

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Date:	Wed, 3 Aug 2016 18:03:34 +0200
From:	"Luis R. Rodriguez" <mcgrof@...nel.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jeff Mahoney <jeffm@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Takashi Iwai <tiwai@...e.de>
Cc:	"Luis R. Rodriguez" <mcgrof@...nel.org>,
	Daniel Wagner <daniel.wagner@...-carit.de>,
	Arend van Spriel <arend.vanspriel@...adcom.com>,
	Bjorn Andersson <bjorn.andersson@...aro.org>,
	Daniel Wagner <wagi@...om.org>,
	Bastien Nocera <hadess@...ess.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Johannes Berg <johannes.berg@...el.com>,
	Kalle Valo <kvalo@...eaurora.org>,
	Ohad Ben-Cohen <ohad@...ery.com>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	David Woodhouse <dwmw2@...radead.org>,
	Julia Lawall <julia.lawall@...6.fr>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	linux-kselftest@...r.kernel.org,
	linux-wireless <linux-wireless@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v0 7/8] Input: ims-pcu: use firmware_stat instead of
 completion

On Wed, Aug 03, 2016 at 12:42:14AM -0700, Dmitry Torokhov wrote:
> On Tue, Aug 2, 2016 at 12:41 AM, Luis R. Rodriguez <mcgrof@...nel.org> wrote:
> > On Tue, Aug 02, 2016 at 08:53:55AM +0200, Daniel Wagner wrote:
> >> On 08/02/2016 08:34 AM, Luis R. Rodriguez wrote:
> >> >On Tue, Aug 02, 2016 at 07:49:19AM +0200, Daniel Wagner wrote:
> >> >>>The sysdata API's main goal rather is to provide a flexible API first,
> >> >>>compartamentalizing the usermode helper was secondary. But now it seems
> >> >>>I may just also add devm support too to help simplify code further.
> >> >>
> >> >>I missed the point that you plan to add usermode helper support to
> >> >>the sysdata API.
> >> >
> >> >I had no such plans, when I have asked folks so far about "hey are you
> >> >really in need for it, OK what for? " and "what extended uses do you
> >> >envision?" so I far I have not gotten any replies at all. So -- instead
> >> >sysdata currently ignores it.
> >>
> >> So you argue for the remoteproc use case with 100+ MB firmware that
> >> if there is a way to load after pivot_root() (or other additional
> >> firmware partition shows up) then there is no need at all for
> >> usermode helper?
> >
> > No, I'm saying I'd like to hear valid uses cases for the usermode helper and so
> > far I have only found using coccinelle grammar 2 explicit users, that's it. My
> > patch series (not yet merge) then annotates these as valid as I've verified
> > through their documentation they have some quirky requirement.
> 
> In certain configurations (embedded) people do not want to use
> initramfs nor modules nor embed firmware into the kernel. In this case
> usermode helper + firmware calss timeout handling provides necessary
> wait for the root filesystem to be mounted.
> 
> If we solve waiting for rootfs (or something else that may contain
> firmware) then these cases will not need to use usermode helper.

Given most distributions already disable FW_LOADER_USER_HELPER_FALLBACK and
grammar shows we only have 2 explicit users of the usermode helper I'd
prefer if we indeed could just compartamentalize the usermode helper
and not rely on it further. Furthermore I think its possible address
this issue, and suggested at least one idea how for now. With a bit
further review I'm in hope we can address this well, not only
for the firmware API but for all other kernel_read_file*() users.

  Luis