linux-kernel - Re: [PATCH v6 3/7] mfd: Add support for the Lantiq PEF2256 framer

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Date:   Thu, 20 Apr 2023 14:47:03 +0100
From:   Lee Jones <lee@...nel.org>
To:     Herve Codina <herve.codina@...tlin.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, alsa-devel@...a-project.org,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v6 3/7] mfd: Add support for the Lantiq PEF2256 framer

On Thu, 20 Apr 2023, Herve Codina wrote:

> On Thu, 20 Apr 2023 13:39:46 +0100
> Lee Jones <lee@...nel.org> wrote:
> 
> > On Mon, 17 Apr 2023, Herve Codina wrote:
> > 
> > > The Lantiq PEF2256 is a framer and line interface component designed to
> > > fulfill all required interfacing between an analog E1/T1/J1 line and the
> > > digital PCM system highway/H.100 bus.
> > > 
> > > Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> > > ---
> > >  drivers/mfd/Kconfig         |  16 +
> > >  drivers/mfd/Makefile        |   1 +
> > >  drivers/mfd/pef2256-regs.h  | 250 ++++++++++
> > >  drivers/mfd/pef2256.c       | 950 ++++++++++++++++++++++++++++++++++++  
> > 
> > 95% of this driver needs to be moved somewhere else.
> > 
> > What is a Framer?  Perhaps sound/ is a good candidate?
> 
> The pef2256 framer is a device that transfers data to/from a TDM (time-slots
> data) from/to quite old telecommunication lines (E1 in my case).
> Several subsystem can set/get data to/from the TDM. Each device using their
> own time-slots set.
> 
> On my use-case, I have some audio consumer and a not yet upstreamed HDLC
> consumer. Both of them uses the framer to know the E1 link state.
> The framer needs to be initialized 'globally' and not by a specific consumer
> as several consumers can use the framer.

I can't think of a good place for this.

If all else fails, it's drivers/misc

> > >  include/linux/mfd/pef2256.h |  52 ++
> > >  5 files changed, 1269 insertions(+)
> > >  create mode 100644 drivers/mfd/pef2256-regs.h
> > >  create mode 100644 drivers/mfd/pef2256.c
> > >  create mode 100644 include/linux/mfd/pef2256.h  
> > 
> > [...]
> > 
> > > +static int pef2256_add_audio_devices(struct pef2256 *pef2256)
> > > +{
> > > +	const char *compatible = "lantiq,pef2256-codec";
> > > +	struct mfd_cell *audio_devs;
> > > +	struct device_node *np;
> > > +	unsigned int count = 0;
> > > +	unsigned int i;
> > > +	int ret;
> > > +
> > > +	for_each_available_child_of_node(pef2256->dev->of_node, np) {
> > > +		if (of_device_is_compatible(np, compatible))
> > > +			count++;
> > > +	}  
> > 
> > Converting Device Tree nodes into MFD cells to register with the
> > Platform Device API is not a reasonable use-case of MFD.
> > 
> > Have the CODEC driver match on "lantiq,pef2256-codec" and let it
> > instantiate itself.
> 
> As the framer is going to used by several subsystem, I cannot instantiate
> it in the specific ASoC subsystem.
> 
> > 
> > Your first version using of_platform_populate() was closer to the mark.
> 
> The issue was that I need MFD cells for the pinctrl part.

Why can't it be represented in DT?

> > > +	if (!count)
> > > +		return 0;
> > > +
> > > +	audio_devs = kcalloc(count, sizeof(*audio_devs), GFP_KERNEL);
> > > +	if (!audio_devs)
> > > +		return -ENOMEM;
> > > +
> > > +	for (i = 0; i < count; i++) {
> > > +		(audio_devs + i)->name = "lantiq-pef2256-codec";
> > > +		(audio_devs + i)->of_compatible = compatible;
> > > +		(audio_devs + i)->id = i;
> > > +	}
> > > +
> > > +	ret = mfd_add_devices(pef2256->dev, 0, audio_devs, count, NULL, 0, NULL);
> > > +	kfree(audio_devs);
> > > +	return ret;
> > > +}  

-- 
Lee Jones [李琼斯]