lkml.org 
[lkml]   [2020]   [Jun]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v4 02/11] mfd: Add support for Kontron sl28cpld management controller
On Wed, 10 Jun 2020, Rob Herring wrote:

> On Wed, Jun 10, 2020 at 1:19 AM Lee Jones <lee.jones@linaro.org> wrote:
> >
> > On Wed, 10 Jun 2020, Michael Walle wrote:
> > > Am 2020-06-09 21:45, schrieb Lee Jones:
> > > > On Tue, 09 Jun 2020, Michael Walle wrote:
> > > > > > We do not need a 'simple-regmap' solution for your use-case.
> > > > > >
> > > > > > Since your device's registers are segregated, just split up the
> > > > > > register map and allocate each sub-device with it's own slice.
> > > > >
> > > > > I don't get it, could you make a device tree example for my
> > > > > use-case? (see also above)
> > > >
> > > > &i2cbus {
> > > > mfd-device@10 {
> > > > compatible = "simple-mfd";
> > > > reg = <10>;
> > > >
> > > > sub-device@10 {
> > > > compatible = "vendor,sub-device";
> > > > reg = <10>;
> > > > };
> > > > };
> > > >
> > > > The Regmap config would be present in each of the child devices.
> > > >
> > > > Each child device would call devm_regmap_init_i2c() in .probe().
> > >
> > > Ah, I see. If I'm not wrong, this still means to create an i2c
> > > device driver with the name "simple-mfd".
> >
> > Yes, it does.
>
> TBC, while fine for a driver to bind on 'simple-mfd', a DT compatible
> with that alone is not fine.

'simple-mfd' essentially means:

"This device doesn't do anything useful, but the children do."

When used with 'syscon' it means:

"Memory for this device is shared between all children"

Adding more specific/descriptive compatible strings is conceptually
fine, but they should not be forced to bind to a real driver using
them. Else we're creating drivers for the sake of creating drivers.

This is especially true with 'simple-mfd' is used without 'syscon'.

> > > Besides that, I don't like this, because:
> > > - Rob already expressed its concerns with "simple-mfd" and so on.
> >
> > Where did this take place? I'd like to read up on this.
> >
> > > - you need to duplicate the config in each sub device
> >
> > You can have a share a single config.
> >
> > > - which also means you are restricting the sub devices to be
> > > i2c only (unless you implement and duplicate other regmap configs,
> > > too). For this driver, SPI and MMIO may be viable options.
> >
> > You could also have a shared implementation to choose between different
> > busses.
>
> I think it is really the syscon mfd driver you want to generalize to
> other buses. Though with a quick look at it, there's not really a
> whole lot to share. The regmap lookup would be the main thing. You are
> going to need a driver instance for each bus type.

On it.

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

\
 
 \ /
  Last update: 2020-06-10 20:03    [W:0.177 / U:0.560 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site