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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Wed, 29 Apr 2020 10:24:45 +0200
Message-ID: <CAK8P3a3vri_-tdEy3x6tRGUjb_k-+Mc+Jt9bQpgFvqm2RN+cJA@mail.gmail.com>
Subject: Re: [PATCH] ASoC: SOF: sort out Kconfig, again
To:     Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Cc:     Daniel Baluta <daniel.baluta@nxp.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        ALSA Development Mailing List <alsa-devel@alsa-project.org>,
        Kai Vehmanen <kai.vehmanen@linux.intel.com>,
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        Fabio Estevam <festevam@gmail.com>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        YueHaibing <yuehaibing@huawei.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Takashi Iwai <tiwai@suse.com>, Mark Brown <broonie@kernel.org>,
        Ranjani Sridharan <ranjani.sridharan@linux.intel.com>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        sound-open-firmware@alsa-project.org,
        Shawn Guo <shawnguo@kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        NXP Linux Team <linux-imx@nxp.com>
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On Wed, Apr 29, 2020 at 1:00 AM Pierre-Louis Bossart
<pierre-louis.bossart@linux.intel.com> wrote:
> >>> Thanks Arnd, do you mind sharing your config?
> >>
> >> https://pastebin.com/HRX5xi3R
> >
> > will give it a try, thanks!
> >
> >>> We noticed last week that
> >>> there's a depend/select confusion might be simpler to fix, see
> >>> https://github.com/thesofproject/linux/pull/2047/commits
> >>>
> >>> If I look at the first line I see a IMX_DSP=n which looks exactly like
> >>> what we wanted to fix.
> >>
> >> Yes, I think that fix addresses the build warning as well, but looking
> >> more closely I don't think it's what you want: If you do this on
> >> a config that has the IMX_DSP disabled, it would appear to the
> >> user that you have enabled the drivers, but the actual code is still
> >> disabled.
> >
> > Are you sure? we added a select IMX_DSP, so not sure how it can be
> > disabled?
>
> I just tested Arnd's config with the patch we came up with for SOF
> (attached) and it makes the unmet dependency go away and builds fine.
> the problem is really using select IMX_DSP if it can be disabled by
> something else. My proposal looks simpler but I will agree it's not
> necessarily super elegant to move the dependency on IMX_BOX into SOF, so
> no sustained objection from me on Arnd's proposal.

Ok, thanks for testing!

I looked at the bigger picture again and found that the more fundamental
problem is the dependency reversal in sound/soc/sof/sof-of-dev.c, where
you have common code that knows about and links against a hardware
specific driver. This is something we try hard do avoid in general in the
kernel, as it causes all kinds of problems:

- Expressing the Kconfig dependencies is rather unnatural and error-prone,
  as you found

- Adding multiple new drivers at the same time leads to merge conflicts

- A kernel that supports multiple SoC families, like all general-purpose
  distros do, and Android is going to do in the future means that you have
  to load every hardware specific module in order to just use one of them.

- In Android's case, it also breaks the model of having one vendor provide
  support for a new SoC by enabling additional modules they ship in
  their vendor specific partition

I think this is all solved by moving the "module_platform_driver()"
and of_device_id array for each driver into the module that defines
the corresponding sof_dev_desc structure, and have those drivers
call the exported sof_of_probe() and sof_of_remove() functions.

      Arnd