Message-ID: <1494180748.13734.6.camel@paulk.fr>
Date:   Sun, 07 May 2017 20:12:28 +0200
From:   Paul Kocialkowski <contact@...lk.fr>
To:     Stephen Warren <swarren@...dotorg.org>,
        Thierry Reding <thierry.reding@...il.com>
Cc:     linux-kernel@...r.kernel.org, alsa-devel@...a-project.org,
        linux-tegra@...r.kernel.org, Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Alexandre Courbot <gnurou@...il.com>,
        Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH 3/3] sound: ASoC: tegra: Select tegra30 i2s and ahub for
 tegra124 SoC

Hi,

Le mardi 25 avril 2017 à 10:57 -0600, Stephen Warren a écrit :
> On 04/24/2017 12:41 PM, Paul Kocialkowski wrote:
> > Le lundi 24 avril 2017 à 09:35 -0600, Stephen Warren a écrit :
> > > On 04/24/2017 09:07 AM, Paul Kocialkowski wrote:
> > > > Le mercredi 19 avril 2017 à 16:00 -0600, Stephen Warren a écrit :
> > > > > On 04/18/2017 10:38 AM, Paul Kocialkowski wrote:
> > > > > > Le mardi 18 avril 2017 à 10:15 -0600, Stephen Warren a écrit :
> > > > > > > On 04/18/2017 09:11 AM, Paul Kocialkowski wrote:
> > > > > > > > This selects the tegra30 i2s and ahub controllers for the
> > > > > > > > tegra124
> > > > > > > > SoC.
> > > > > > > > These are needed when building without ARCH_TEGRA_3x_SOC set.
> > > > > > > > diff --git a/sound/soc/tegra/Kconfig b/sound/soc/tegra/Kconfig
> > > > > > > > index efbe8d4c019e..bcd18d2cf7a7 100644
> > > > > > > > --- a/sound/soc/tegra/Kconfig
> > > > > > > > +++ b/sound/soc/tegra/Kconfig
> > > > > > > > @@ -46,7 +46,7 @@ config SND_SOC_TEGRA20_SPDIF
> > > > > > > > 
> > > > > > > >  config SND_SOC_TEGRA30_AHUB
> > > > > > > >  	tristate
> > > > > > > > -	depends on SND_SOC_TEGRA && ARCH_TEGRA_3x_SOC
> > > > > > > > +	depends on SND_SOC_TEGRA && (ARCH_TEGRA_3x_SOC ||
> > > > > > > > ARCH_TEGRA_124_SOC)
> > > > > > > 
> > > > > > > Is this really a compile-time dependency?
> > > > > > 
> > > > > > From a quick look at the code, I doubt this is really a build
> > > > > > dependency.
> > > > > > 
> > > > > > > If so, don't we need to add T210 and T186 entries into that ||
> > > > > > > condition
> > > > > > > too,
> > > > > > > since we could be building a kernel with just T210/T186 support
> > > > > > > and no
> > > > > > > T124
> > > > > > > support?
> > > > > > 
> > > > > > In the spirit of this patch, adding entries for other tegra
> > > > > > platforms
> > > > > > would
> > > > > > make
> > > > > > sense. Would you prefer that we leave out the dependency from
> > > > > > SND_SOC_TEGRA30_*
> > > > > > and only select the right I2S driver to use in each codec driver?
> > > > > > 
> > > > > > If not, we'd have to list all relevant platforms both in the
> > > > > > I2S/AHUB
> > > > > > drivers
> > > > > > and in each codec's rules (which is not necessarily and issue, but
> > > > > > there's
> > > > > > no
> > > > > > need to have artificial platform dependencies).
> > > > > > 
> > > > > > What do you think?
> > > > > 
> > > > > I think we should just remove most of these "depends on" since they're
> > > > > mostly set up to reflect runtime requirements rather than build time
> > > > > requirements. The only points I'd make are:
> > > > 
> > > > I definitely agree we should do that for all the codec Kconfig options.
> > > > 
> > > > > 1)
> > > > > 
> > > > > Everything should "depends on SND_SOC_TEGRA" simply so the options
> > > > > don't
> > > > > show up and clutter menuconfig menus unless SND_SOC_TEGRA is enabled.
> > > > 
> > > > Agreed.
> > > > 
> > > > > 2)
> > > > > 
> > > > > SND_SOC_TEGRA30_I2S does need the Tegra30 AHUB driver in order to
> > > > > compile/link, since it directly calls functions in that driver. This
> > > > > is
> > > > > already handled by SND_SOC_TEGRA30_I2S doing "select
> > > > > SND_SOC_TEGRA30_AHUB".
> > > > 
> > > > Agreed.
> > > > 
> > > > > 3)
> > > > > 
> > > > > The machine drivers all do e.g. "select SND_SOC_TEGRA30_I2S if
> > > > > ARCH_TEGRA_3x_SOC". This was an attempt to make the machine drivers
> > > > > only
> > > > > pull in the relevant drivers for the SoC(s) being compiled for. I'm
> > > > > not
> > > > > sure this still makes sense; this won't work on kernels that only
> > > > > support T124/T210/T186 since ARCH_TEGRA_3x_SOC isn't enabled then.
> > > > > Should we just remove all those and make sure the defconfigs are
> > > > > updated
> > > > > to make sure the relevant I2S/AHUB/SPDIF/AC97 drivers are explicitly
> > > > > enabled? Perhaps we should default all the I2S/AHUB/SPDIF/AC97 to y
> > > > > (which will only apply if SND_SOC_TEGRA is enabled)?
> > > > 
> > > > I think it would be easier for everyone to just auto-select the machine
> > > > drivers
> > > > automatically based on the architecture (so we could have the list of
> > > > ARCH_TEGRA_*_SOC here) when SND_SOC_TEGRA is selected.
> > > 
> > > I don't think selecting the machine drivers is the correct approach,
> > > since then they can't be disabled.
> > > 
> > > Making certain machine drivers "default y if ARCH_TEGRA_nn_SOC" would
> > > address that,
> > 
> > That's right, my mistake. Let's take that as the solution I'm backing then.
> > 
> > >  but still isn't very scalable since we need to go back and
> > > edit the Kconfig every time we define a new SoC, in order to add that
> > > SoC into the default statement.
> > 
> > Well, that's what platform bringup is all about, isn't it? I think it makes
> > a
> > lot more sense to have to add a new platform once (and it's not like one
> > will
> > forget to look at the sound part when adding a new platform) rather than
> > requiring users to hand-pick the option.
> 
> Personally I'd expect all the Tegra machine drivers to be enabled in the 
> upstream defconfig files all the time, such that we don't need to make 
> the Kconfig options default y, nor have users manually turn the relevant 
> options on, at all.

I think I was previously mistaken about what the machine drivers are, so I got a
good occasion to find out about them an learn something new. Thanks!

Agreed regarding the machine drivers, they should indeed all be enabled in the
defconfig by default.

> > > > Not only does this preserve existing configs (including external ones
> > > > that
> > > > aren't part of the kernel tree), it also clearly maps which machine
> > > > driver
> > > > to use for which SoC instead of having users do it by hand.
> > > 
> > > The machine drivers aren't terribly tied to SoCs by design; most of them
> > > would work on pretty much any SoC. They're only tied to SoCs as a
> > > side-effect of a machine driver being tied to a certain CODEC, and
> > > certain CODECS just by chance are only used (so far) on specific boards,
> > > which have specific SoCs.
> > 
> > I'm a bit confused: aren't the machine driver (i2s/ahub/spdif/ac97) tied to
> > specific hardware blocks that are found in specific SoCs and not in others?
> > I
> > can see these blocks haven't evolved much across generations, but they're
> > still
> > either part of a specific SoC or not, aren't they?
> > 
> > The compatible strings in the common SoC dts seem to indicate that only one
> > of
> > these blocks is found at a time.
> 
> There are SoC-specific drivers for the components (Tegra20 I2S, Tegra30 
> I2S, etc.), but the *machine* drivers generally don't know anything 
> about that. DT instantiates the correct component drivers for the SoC, 
> and the machine driver just uses whatever it's linked to without caring 
> too-much/at-all about whether it's hooked to a Tegra20 I2S or a Tegra30 
> I2S device.

That makes sense now. Regarding the SoC-specific components, would you agree
with auto-selecting those based on ARCH_TEGRA_xx_SOC so that only the required
drivers are pulled-in? Otherwise, I'm also fine with explicitely enabling them
in the defconfig at this point.

Cheers,

-- 
Paul Kocialkowski, developer of free digital technology and hardware support

Website: https://www.paulk.fr/
Coding blog: https://code.paulk.fr/
Git repositories: https://git.paulk.fr/ https://git.code.paulk.fr/
Download attachment "signature.asc" of type "application/pgp-signature" (834 bytes)

Powered by blists - more mailing lists