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

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Date:   Fri, 21 Apr 2023 09:26:45 +0200
From:   Herve Codina <herve.codina@...tlin.com>
To:     Lee Jones <lee@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     Rob Herring <robh+dt@...nel.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

Hi Lee, Krzysztof,

On Thu, 20 Apr 2023 14:47:03 +0100
Lee Jones <lee@...nel.org> wrote:

> 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?

The pinctrl part has no specific compatible string.
Not sure that a compatible string for pinctrl can be accepted
as there is only one pinctrl subnode and no specific reg for this
subnode.

The DT looks like this:
    framer@...0000 {
      compatible = "lantiq,pef2256";
      reg = <0x2000000 0x100>;
      ...
      pinctrl {
        pef2256_rpa_sypr: rpa-pins {
          pins = "RPA";
          function = "SYPR";
        };
      };

      pef2256_codec0: codec-0 {
        compatible = "lantiq,pef2256-codec";
        #sound-dai-cells = <0>;
        sound-name-prefix = "PEF2256_0";
      };
    };

Krzysztof, is it acceptable to have a compatible string in the pinctrl node ?
In this case, it will looks like this:
    framer@...0000 {
      compatible = "lantiq,pef2256";
      reg = <0x2000000 0x100>;
      ...
      pinctrl {
        compatible = "lantiq,pef2256-pinctrl";
        pef2256_rpa_sypr: rpa-pins {
          pins = "RPA";
          function = "SYPR";
        };
      };

      pef2256_codec0: codec-0 {
        compatible = "lantiq,pef2256-codec";
        #sound-dai-cells = <0>;
        sound-name-prefix = "PEF2256_0";
      };
    };

Best regards,
Hervé