linux-kernel - Re: [PATCH] ALSA: hda: fix SND_INTEL_DSP

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Message-ID: <CAK8P3a0PXXHXLK36SB_4eia6z0u3nbBPanATwZEhposKOScqcw@mail.gmail.com>
Date:   Tue, 5 Jan 2021 20:06:18 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Kai Vehmanen <kai.vehmanen@...ux.intel.com>
Cc:     Takashi Iwai <tiwai@...e.de>, Jaroslav Kysela <perex@...ex.cz>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Takashi Iwai <tiwai@...e.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Daniel Baluta <daniel.baluta@....com>,
        ALSA Development Mailing List <alsa-devel@...a-project.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        sound-open-firmware@...a-project.org
Subject: Re: [PATCH] ALSA: hda: fix SND_INTEL_DSP_CONFIG dependency

On Tue, Jan 5, 2021 at 4:39 PM Kai Vehmanen
<kai.vehmanen@...ux.intel.com> wrote:

> > Could it be part of the device specific driver_data?
>
> This would certainly be a clean way and allow to remove the Intel-specific
> calls from sof_pci_probe(). As a short-term solution, IS_REACHABLE()
> seems ok as well.

I looked at it some more and my conclusion is that the problem is
the way the drivers mix device specific and generic data: The generic
acpi or pci driver should never need to know about individual devices
and their dependencies. Instead of just exporting some generic
helper functions, these are the top-level drivers and the device
specific drivers are the ones exporting the data.

It's a common mistake,  but it always leads to complexity like this
and we tend to end up having to undo it all.

I prototyped a patch to do this for the acpi driver, and it seems
much more straightforward this way, please have a look.

commit a83ecfed5b31dfc862e04c9bf77d2107a1047c9b
Author: Arnd Bergmann <arnd@...db.de>
Date:   Tue Jan 5 19:47:35 2021 +0100

    ASoC: SOF: Intel: avoid reverse module dependency

    The SOF-ACPI driver is backwards from the normal Linux model, it has a
    generic driver that knows about all the specific drivers, as opposed to
    having hardware specific drivers that link against a common framework.

    This requires ugly Kconfig magic and leads to missed dependencies as
    seen in this link error:

    arm-linux-gnueabi-ld: sound/soc/sof/sof-pci-dev.o: in function
`sof_acpi_probe':
    sof-pci-dev.c:(.text+0x1c): undefined reference to
`snd_intel_dsp_driver_probe'

    Change it to use the normal probe order of starting with a specific
    device in a driver, turning the sof-acpi-dev.c driver into a library.

    Signed-off-by: Arnd Bergmann <arnd@...db.de>

 sound/soc/sof/intel/Kconfig  |  34 +++---------
 sound/soc/sof/intel/bdw.c    |  51 ++++++++++++++++--
 sound/soc/sof/intel/byt.c    | 104 ++++++++++++++++++++++++++++++++----
 sound/soc/sof/intel/shim.h   |  10 ++--
 sound/soc/sof/sof-acpi-dev.c | 122 ++-----------------------------------------
 5 files changed, 156 insertions(+), 165 deletions(-)

The PCI driver is left as an exercise to the reader.

      Arnd