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Date: Mon, 24 Apr 2023 10:52:00 +0100
From: Lee Jones <lee@...nel.org>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: Herve Codina <herve.codina@...tlin.com>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
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
On Fri, 21 Apr 2023, Krzysztof Kozlowski wrote:
> On 21/04/2023 09:45, Lee Jones wrote:
> > On Fri, 21 Apr 2023, Herve Codina wrote:
> >
> >> 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 ?
> >
> > Why wouldn't it be?
> >
> > $ git grep ".compatible" -- drivers/pinctrl/
> >
> >> In this case, it will looks like this:
> >> framer@...0000 {
> >> compatible = "lantiq,pef2256";
> >> reg = <0x2000000 0x100>;
> >> ...
> >> pinctrl {
> >> compatible = "lantiq,pef2256-pinctrl";
>
> If you do not have any resources, there is no point in having separate
> compatible for separate device node.
That's a new rule. Is that documented somewhere? I'm sure we already
have device nodes for devices whom only operate on shared resources.
> Anyway this discussions should not be about DT. How Linux drivers are
> implementing DT is not really a guide how to write DT. Since these
> series were brought there were some DT decisions made based how you want
> to write the driver. No, please don't. I also do not see any problems in
> handling more-or-less complex driver structures without poking the DT.
> We have already many such device families.
--
Lee Jones [李琼斯]
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