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From: Lee Jones <lee.jones@linaro.org>
To: Michael Walle <michael@walle.cc>
Cc: "Andy Shevchenko" <andy.shevchenko@gmail.com>,
	"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, 8 Jun 2020 19:56:51 +0100
Message-ID: <20200608185651.GD4106@dell> (raw)
In-Reply-To: <7d7feb374cbf5a587dc1ce65fc3ad672@walle.cc>

On Mon, 08 Jun 2020, Michael Walle wrote:

> 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.

Then what's stopping you having each device Regmap their own space?

The issues I wish to resolve using 'simple-mfd' are when sub-devices
register maps overlap and intertwine.

> > > > > > 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)

I don't see an issue with that.  I would put that check inside a
shared call though, complete with support for locking.

> > > > > >  (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.

And you wish for users to be able to view these at run-time?

Can they adapt any of them on-the-fly or will the be RO?

> > > > > 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?

Whatever is in the 'reg' property contained in the Device Tree node.
Either the full address or an offset would be suitable.

Caveat: All this thinking has been done on-the-fly.  I would need to
look at some examples of existing devices and start coding before I
could really think the solution through.

Happy to discuss and/or take recommendations though.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog

  reply index

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
2020-06-08 18:56                   ` Lee Jones [this message]
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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