linux-kernel - Re: [RFC PATCH 00/34] sun8i-codec fixes and new features

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Message-ID: <20200217120719.m37dldhe5fshcw27@gilmour.lan>
Date:   Mon, 17 Feb 2020 13:07:19 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Samuel Holland <samuel@...lland.org>,
        Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Mylène Josserand 
        <mylene.josserand@...e-electrons.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 00/34] sun8i-codec fixes and new features

On Mon, Feb 17, 2020 at 05:44:36PM +0800, Chen-Yu Tsai wrote:
> On Mon, Feb 17, 2020 at 5:14 PM Maxime Ripard <maxime@...no.tech> wrote:
> >
> > Hi,
> >
> > On Mon, Feb 17, 2020 at 12:42:16AM -0600, Samuel Holland wrote:
> > > The sun8i-codec driver, as used in the Allwinner A33 and A64, currently
> > > only exposes a small subset of the available hardware features. In order
> > > to use the A64 in a smartphone (the PinePhone), I've added the necessary
> > > functionality to the driver:
> > >   * The full set of supported DAI format options
> > >   * Support for AIF2 and AIF3
> > >   * Additional routing knobs
> > >   * Additional volume controls
> > >
> > > Unfortunately, due to preexisting issues with the driver, there are some
> > > breaking changes, as explained further in the commit messages:
> > >   * The LRCK inversion issue means we need a new compatible for the A64.
> > >   * Some controls are named inaccurately, so they are renamed.
> > >   * Likewise, the DAPM widgets used in device trees were either named
> > >     wrong, or the device trees were using the wrong widgets in the first
> > >     place. (Specifically, the links between the analog codec and digital
> > >     codec happen at the ADC and DAC, not AIF1.)
> > >
> > > I tended to take the philosophy of "while I'm breaking things, I might
> > > as well do them right", so I've probably made a few more changes than
> > > absolutely necessary. I'm not sure about where all of the policy
> > > boundaries are, about how far I should go to maintain compatibility. For
> > > example, for the DT widget usage, I could:
> > >   * Rename everything and update the DTS files (which is what I did)
> > >   * Keep the old (misleading/wrong) name for the widgets, but repurpose
> > >     them to work correctly
> > >       (i.e. "ADC Left" would be named "AIF1 Slot 0 Left ADC", but it
> > >        would work just like "ADC Left" does in this patchset)
> > >   * Keep the old widgets around as a compatibility layer, but add new
> > >     widgets and update the in-tree DTS files to use them
> > >       (i.e. "ADC Left" would have a path from "AIF1 Slot 0 Left ADC",
> > >        but "AIF1 Slot 0 Left ADC" would be a no-op widget)
> > >   * Something else entirely
> >
> > I'm not sure this is really a concern here. We need to maintain the
> > compatibility with old DT's, but those will have an A33 compatible
> > too, and as far as I can see, you're not changing anything for that
> > compatible, so we're in the clear?
> >
> > If not, then the third option would probably be the best, especially
> > since it's only a couple of them.
>
> Unfortunately the description for both chips are shared, and they're wrong.
> So we probably need a new compatible (or a new driver)... or like options
> 2 or 3, keep the DT visible endpoints (but deprecate them), and route them
> to a new set of proper widgets.

And hmm, it might be a bit wild, but since it's basically just a sed
on a string in DT, can't we leverage the dynamic DT stuff to rewrite
the property if we find the old one at probe? That would keep the
driver clean.

Maxime