From: Michael Walle <michael@walle.cc>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: "Lee Jones" <lee.jones@linaro.org>,
"Ranjani Sridharan" <ranjani.sridharan@linux.intel.com>,
david.m.ertman@intel.com, shiraz.saleem@intel.com,
"Rob Herring" <robh+dt@kernel.org>,
"Mark Brown" <broonie@kernel.org>,
"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
devicetree <devicetree@vger.kernel.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
linux-hwmon@vger.kernel.org, linux-pwm@vger.kernel.org,
linux-watchdog@vger.kernel.org,
"linux-arm Mailing List" <linux-arm-kernel@lists.infradead.org>,
"Linus Walleij" <linus.walleij@linaro.org>,
"Bartosz Golaszewski" <bgolaszewski@baylibre.com>,
"Jean Delvare" <jdelvare@suse.com>,
"Guenter Roeck" <linux@roeck-us.net>,
"Thierry Reding" <thierry.reding@gmail.com>,
"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
"Wim Van Sebroeck" <wim@linux-watchdog.org>,
"Shawn Guo" <shawnguo@kernel.org>, "Li Yang" <leoyang.li@nxp.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Jason Cooper" <jason@lakedaemon.net>,
"Marc Zyngier" <maz@kernel.org>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>
Subject: Re: [PATCH v4 02/11] mfd: Add support for Kontron sl28cpld management controller
Date: Mon, 08 Jun 2020 17:41:51 +0200 [thread overview]
Message-ID: <7d7feb374cbf5a587dc1ce65fc3ad672@walle.cc> (raw)
In-Reply-To: <CAHp75VdiH=J-ovCdh1RFJDW_bJM8=pbXRaHmB691GLb-5oBmYQ@mail.gmail.com>
Am 2020-06-08 12:02, schrieb Andy Shevchenko:
> +Cc: some Intel people WRT our internal discussion about similar
> problem and solutions.
>
> On Mon, Jun 8, 2020 at 11:30 AM Lee Jones <lee.jones@linaro.org> wrote:
>> On Sat, 06 Jun 2020, Michael Walle wrote:
>> > Am 2020-06-06 13:46, schrieb Mark Brown:
>> > > On Fri, Jun 05, 2020 at 10:07:36PM +0200, Michael Walle wrote:
>> > > > Am 2020-06-05 12:50, schrieb Mark Brown:
>
> ...
>
>> Right. I'm suggesting a means to extrapolate complex shared and
>> sometimes intertwined batches of register sets to be consumed by
>> multiple (sub-)devices spanning different subsystems.
>>
>> Actually scrap that. The most common case I see is a single Regmap
>> covering all child-devices.
>
> Yes, because often we need a synchronization across the entire address
> space of the (parent) device in question.
>
>> It would be great if there was a way in
>> which we could make an assumption that the entire register address
>> space for a 'tagged' (MFD) device is to be shared (via Regmap) between
>> each of the devices described by its child-nodes. Probably by picking
>> up on the 'simple-mfd' compatible string in the first instance.
>>
>> Rob, is the above something you would contemplate?
>>
>> Michael, do your register addresses overlap i.e. are they intermingled
>> with one another? Do multiple child devices need access to the same
>> registers i.e. are they shared?
No they don't overlap, expect for maybe the version register, which is
just there once and not per function block.
>>
>> > > > But, there is more in my driver:
>> > > > (1) there is a version check
>>
>> If we can rid the Regmap dependency, then creating an entire driver to
>> conduct a version check is unjustifiable. This could become an inline
>> function which is called by each of the sub-devices instead, for
>> example.
sounds good to me. (although there would then be a probe fail per
sub-device
if the version is not supported)
>> > > > (2) there is another function for which there is no suitable linux
>> > > > subsystem I'm aware of and thus which I'd like to us sysfs
>> > > > attributes for: This controller supports 16 non-volatile
>> > > > configuration bits. (this is still TBD)
>>
>> There is a place for everything in Linux.
>>
>> What do these bits configure?
- hardware strappings which have to be there before the board powers up,
like clocking mode for different SerDes settings
- "keep-in-reset" bits for onboard peripherals if you want to save power
- disable watchdog bits (there is a watchdog which is active right from
the start and supervises the bootloader start and switches to failsafe
mode if it wasn't successfully started)
- special boot modes, like eMMC, etc.
Think of it as a 16bit configuration word.
>> > > TBH I'd also say that the enumeration of the subdevices for this
>> > > device should be in the device rather than the DT, they don't
>> > > seem to be things that exist outside of this one device.
>> >
>> > We're going circles here, formerly they were enumerated in the MFD.
>> > Yes, they are devices which aren't likely be used outside a
>> > "sl28cpld", but there might there might be other versions of the
>> > sl28cpld with other components on different base addresses. I
>> > don't care if they are enumerated in DT or MFD, actually, I'd
>> > prefer the latter. _But_ I would like to have the device tree
>> > properties for its subdevices, e.g. the ones for the watchdog or
>> > whatever components there might be in the future.
>>
>> [...]
>>
>> > MFD core can
>> > match a device tree node today; but only one per unique compatible
>> > string. So what should I use to differentiate the different
>> > subdevices?
>>
>> Right. I have been aware of this issue. The only suitable solution
>> to this would be to match on 'reg'.
see below (1)
>>
>> FYI: I plan to fix this.
>>
>> If your register map needs to change, then I suggest that this is
>> either a new device or at least a different version of the device and
>> would also have to be represented as different (sub-)mfd_cell.
>>
>> > Rob suggested the internal offset, which I did here.
>>
>> FWIW, I don't like this idea. DTs should not have to be modified
>> (either in the first instance or subsequently) or specifically
>> designed to patch inadequacies in any given OS.
How does (1) play together with this? What do you propose the "reg"
property should contain?
>>
>> > But then, there is less use in duplicating the offsets in the MFD
>> > just to have the MFD enumerate the subdevices and then match
>> > the device tree nodes against it. I can just use
>> > of_platform_populate() to enumerate the children and I won't
>> > have to duplicate the base addresses.
>>
>> Which is fine. However this causes a different issue for you. By
>> stripping out the MFD code you render the MFD portion seemingly
>> superfluous. Another issue driver authors commonly contend with.
Yeah, I agree.
-michael
next prev parent reply other threads:[~2020-06-08 15:41 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-04 21:10 [PATCH v4 00/11] Add support for Kontron sl28cpld Michael Walle
2020-06-04 21:10 ` [PATCH v4 01/11] dt-bindings: mfd: Add bindings for sl28cpld Michael Walle
2020-06-09 16:28 ` Rob Herring
2020-06-04 21:10 ` [PATCH v4 02/11] mfd: Add support for Kontron sl28cpld management controller Michael Walle
2020-06-05 6:57 ` Lee Jones
2020-06-05 9:51 ` Michael Walle
2020-06-05 10:50 ` Mark Brown
2020-06-05 20:07 ` Michael Walle
2020-06-06 11:46 ` Mark Brown
2020-06-06 12:45 ` Michael Walle
2020-06-08 8:28 ` Lee Jones
2020-06-08 10:02 ` Andy Shevchenko
2020-06-08 15:41 ` Michael Walle [this message]
2020-06-08 18:56 ` Lee Jones
2020-06-08 21:09 ` Michael Walle
2020-06-09 6:47 ` Lee Jones
2020-06-09 14:38 ` Michael Walle
2020-06-09 14:42 ` Mark Brown
2020-06-09 15:01 ` Michael Walle
2020-06-09 17:15 ` Rob Herring
2020-06-09 17:29 ` Mark Brown
2020-06-09 18:41 ` Lee Jones
2020-06-09 15:19 ` Lee Jones
2020-06-09 15:30 ` Michael Walle
2020-06-09 19:45 ` Lee Jones
2020-06-10 7:10 ` Michael Walle
2020-06-10 7:19 ` Lee Jones
2020-06-10 7:49 ` Michael Walle
2020-06-10 7:56 ` Lee Jones
2020-06-10 9:27 ` Michael Walle
2020-06-10 18:30 ` Lee Jones
2020-06-10 17:16 ` Rob Herring
2020-06-10 18:02 ` Lee Jones
2020-06-08 18:20 ` Lee Jones
2020-06-09 16:54 ` Rob Herring
2020-06-09 18:52 ` Lee Jones
2020-06-05 8:01 ` Andy Shevchenko
2020-06-05 8:02 ` Andy Shevchenko
2020-06-05 10:09 ` Michael Walle
2020-06-05 10:48 ` Andy Shevchenko
2020-06-05 11:51 ` Michael Walle
2020-06-04 21:10 ` [PATCH v4 03/11] irqchip: add sl28cpld interrupt controller support Michael Walle
2020-06-05 1:26 ` kernel test robot
2020-06-05 8:07 ` Andy Shevchenko
2020-06-08 15:12 ` kernel test robot
2020-06-04 21:10 ` [PATCH v4 04/11] watchdog: add support for sl28cpld watchdog Michael Walle
2020-06-05 8:14 ` Andy Shevchenko
2020-06-05 10:24 ` Michael Walle
2020-06-05 10:50 ` Andy Shevchenko
2020-06-05 13:52 ` Guenter Roeck
2020-06-05 14:09 ` Andy Shevchenko
2020-06-05 15:05 ` Guenter Roeck
2020-06-05 16:04 ` Andy Shevchenko
2020-06-05 16:34 ` Guenter Roeck
2020-06-04 21:10 ` [PATCH v4 05/11] pwm: add support for sl28cpld PWM controller Michael Walle
2020-06-05 8:15 ` Andy Shevchenko
2020-06-05 8:49 ` Lee Jones
2020-06-05 9:33 ` Andy Shevchenko
2020-06-05 11:39 ` Michael Walle
2020-06-05 18:17 ` Michael Walle
2020-06-08 7:46 ` Lee Jones
2020-06-04 21:10 ` [PATCH v4 06/11] gpio: add support for the sl28cpld GPIO controller Michael Walle
2020-06-05 12:00 ` Andy Shevchenko
2020-06-05 12:42 ` Michael Walle
2020-06-05 13:15 ` Andy Shevchenko
2020-06-05 18:44 ` Michael Walle
2020-06-05 21:19 ` Andy Shevchenko
2020-06-04 21:10 ` [PATCH v4 07/11] hwmon: add support for the sl28cpld hardware monitoring controller Michael Walle
2020-06-05 12:06 ` Andy Shevchenko
2020-06-04 21:10 ` [PATCH v4 08/11] arm64: dts: freescale: sl28: enable sl28cpld Michael Walle
2020-06-04 21:10 ` [PATCH v4 09/11] arm64: dts: freescale: sl28: map GPIOs to input events Michael Walle
2020-06-04 21:10 ` [PATCH v4 10/11] arm64: dts: freescale: sl28: enable LED support Michael Walle
2020-06-04 21:10 ` [PATCH v4 11/11] arm64: dts: freescale: sl28: enable fan support Michael Walle
2020-06-05 6:13 ` [PATCH v4 00/11] Add support for Kontron sl28cpld Lee Jones
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