linux-kernel - Re: [PATCH v5 2/2] dt-bindings: mediatek: mt6359: add codec document

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Date:   Mon, 7 Sep 2020 21:37:12 +0800
From:   Tzung-Bi Shih <tzungbi@...gle.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Jiaxin Yu <jiaxin.yu@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Takashi Iwai <tiwai@...e.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ALSA development <alsa-devel@...a-project.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, howie.huang@...iatek.com,
        eason.yen@...iatek.com, shane.chien@...iatek.com,
        bicycle.tsai@...iatek.com
Subject: Re: [PATCH v5 2/2] dt-bindings: mediatek: mt6359: add codec document

On Thu, Aug 20, 2020 at 3:40 AM Mark Brown <broonie@...nel.org> wrote:
>
> On Wed, Aug 19, 2020 at 11:42:27PM +0800, Tzung-Bi Shih wrote:
>
> > But I found struct mfd_cell also contains member .of_compatible.  What
> > is the difference if we use compatible string (as is) for this device
> > instead of falling back to use device name to match?
>
> That's for binding the MFD subdevice to an OF node, you don't need to do
> that for a device like this - you can just use the of_node of the parent
> to get at the properties.

There is an issue we overlooked.  In sound/soc/codecs/mt6359.c,
mt6359_parse_dt() cannot read the DT properties
(https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git/tree/sound/soc/codecs/mt6359.c?h=for-next#n2640).

The original DTS is as following:
pmic {
  compatible = "mediatek,mt6359";

  mt6359codec: mt6359codec {
    compatible = "mediatek,mt6359-sound";  (1)
    mediatek,dmic-mode = <1>;
    mediatek,mic-type-0 = <2>;
  }
}
After removing the line at (1), mt6359_parse_dt() cannot read the DT properties.

The PMIC drivers/mfd/mt6397-core.c:
- "mediatek,mt6359"
- has the struct mfd_cell of mt6359-sound
- adds all mfd_cells via devm_mfd_add_devices().

The audio codec sound/soc/codecs/mt6359.c:
- "mediatek,mt6359-sound"


Here are a few options we can come out with.
1. adds back the compatible string in the DTS
2. gets of_node of parent in mt6359.c, and iterates all children nodes
to get the desired properties
3. parses all children nodes in the PMIC driver, and put them into
either platform_data or device properties
(https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git/tree/include/linux/mfd/core.h?h=for-next#n77)
- The PMIC is common for several sub-devices.  It makes less sense to
handle subdevice specific logic in the common code.
4. others

Could you share with us what would you suggest for fixing the issue?