linux-kernel - Re: [RFC PATCH 0/5] Add CONFIG symbol as module attribute

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Message-ID: <40f70582-c16a-7de0-cfd6-c7d5ff9ead71@metux.net>
Date:   Wed, 3 Jul 2019 14:16:44 +0200
From:   "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
To:     Luis Chamberlain <mcgrof@...nel.org>,
        Christoph Hellwig <hch@....de>
Cc:     Brendan Higgins <brendanhiggins@...gle.com>,
        Cristina Moraru <cristina.moraru09@...il.com>,
        "vegard.nossum@...il.com" <vegard.nossum@...il.com>,
        Valentin Rothberg <valentinrothberg@...il.com>,
        Hannes Reinecke <hare@...e.de>,
        Sam Ravnborg <sam@...nborg.org>,
        Michal Marek <mmarek@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Tom Gundersen <teg@...m.no>, Kay Sievers <kay@...y.org>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        backports@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "rafael.j.wysocki" <rafael.j.wysocki@...el.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Takashi Iwai <tiwai@...e.de>,
        Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Johannes Berg <johannes@...solutions.net>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Paul Bolle <pebolle@...cali.nl>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        Sathya Prakash Veerichetty <sathya.prakash@...adcom.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Laurence Oberman <loberman@...hat.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Tejun Heo <tj@...nel.org>,
        Jej B <James.Bottomley@...senpartnership.com>,
        Theodore Ts'o <tytso@....edu>,
        Daniel Jonsson <danijons@...dent.chalmers.se>,
        Andrzej Wasowski <wasowski@....dk>
Subject: Re: [RFC PATCH 0/5] Add CONFIG symbol as module attribute

On 28.06.19 20:40, Luis Chamberlain wrote:

Hi folks,

> The solution puts forward a mechanism to add a kconfig_symb where we> are 100% certain we have a direct module --> config mapping.
Okay, but IIRC this will add more boilerplate those modules.

And I wonder whether target binaries are the right place for those
things at all - IMHO that's something one wants to derive from the
source code  / .config's. At least in the cases I'm imagining, I don't
even have an actual kernel running on the corresponding target yet.
(eg. in crosscompile situations)

OTOH, a more pressing problem for me is identifying the right drivers
and corresponding config options (usually plural, as certain subsystems
have to be enabled, too) by hardware information like DT, ACPI, DMI,
PCI, etc. For now, I have to do that manually, which is pretty time
consuming.

In embedded world, we often have scenarios where we want a really
minimal kernel, but need to enable/disable certain hi-level peripherals
in the middle of the project (eg. "oh, we also need ethernet, but we
wanna drop usb"). There we'll have to find out what actual chip is,
its corresponding driver, required subsystems, etc, and also kick off
everything we don't need anymore.

I've thought about implementing some actual dependency tracking
(at least recording the auto-enabled symbols), but didn't expect that
to become practically usable anytime soon, so I went for a different
approach: writing a little tool that allows modeling hilevel features
and corresponding (potentially board-specific) config syms, so the whole
.config for certain board and usecase can be autogenerated by just some
small meta-configuration:

   https://github.com/metux/kmct

Maybe this could also help for your usecase ?


--mtx

-- 
Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@...ux.net -- +49-151-27565287