Re: [[PATCH v2] 1/9] dt-bindings: pwm: Document Synopsys DesignWare snps,pwm

[Ben Dooks]

On 27/07/2022 13:02, Krzysztof Kozlowski wrote:
> On 27/07/2022 12:32, Ben Dooks wrote:
> > On 26/07/2022 12:05, Krzysztof Kozlowski wrote:
> > > On 26/07/2022 12:12, Ben Dooks wrote:
> > > > On 26/07/2022 11:05, Krzysztof Kozlowski wrote:
> > > > > On 25/07/2022 23:21, Ben Dooks wrote:
> > > > > > Add documentation for the bindings for Synopsys' DesignWare PWM block
> > > > > > as we will be adding DT/platform support to the Linux driver soon.
> > > > > >
> > > > > > Signed-off-by: Ben Dooks <ben.dooks@xxxxxxxxxx>
> > > > > > --
> > > > >
> > > > > This is not proper delimiter and causes the changelog to end up in commit.
> > > > >
> > > > > Correct also wrong formatting of subject PATCH.
> > > >
> > > > I realised that once sent and forgot the cover letter.
> > > > Maybe I'll try some more post covid recovery.
> > > >
> > > > > > v2:
> > > > > > - fix #pwm-cells to be 3
> > > > > > - fix indentation and ordering issues
> > > > > > ---
> > > > > >     .../devicetree/bindings/pwm/snps,pwm.yaml     | 40 +++++++++++++++++++
> > > > > >     1 file changed, 40 insertions(+)
> > > > > >     create mode 100644 Documentation/devicetree/bindings/pwm/snps,pwm.yaml
> > > > > >
> > > > > > diff --git a/Documentation/devicetree/bindings/pwm/snps,pwm.yaml b/Documentation/devicetree/bindings/pwm/snps,pwm.yaml
> > > > > > new file mode 100644
> > > > > > index 000000000000..594085e5e26f
> > > > > > --- /dev/null
> > > > > > +++ b/Documentation/devicetree/bindings/pwm/snps,pwm.yaml
> > > > > > @@ -0,0 +1,40 @@
> > > > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > > > +# Copyright (C) 2022 SiFive, Inc.
> > > > > > +%YAML 1.2
> > > > > > +---
> > > > > > +$id: http://devicetree.org/schemas/pwm/snps,pwm.yaml#
> > > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > > > +
> > > > > > +title: Synopsys PWM controller
> > > > > > +
> > > > > > +maintainers:
> > > > > > +  - Ben Dooks <ben.dooks@xxxxxxxxxx>
> > > > > > +
> > > > > > +allOf:
> > > > > > +  - $ref: pwm.yaml#
> > > > > > +
> > > > > > +properties:
> > > > > > +  compatible:
> > > > > > +    const: snps,pwm
> > > > >
> > > > > This is very generic compatible. I doubt that you cover here all
> > > > > Synopsys PWM designs, past and future. You need a specific compatible.
> > > >
> > > >    From what I can get from the documentation (2.13a) there hasn't been
> > > > a huge external interface change and what has been added is all part
> > > > of synthesis time options.
> > >
> > > But you have some specific version, right? Usually these blocks are
> > > versioned, so you must include it. I would even argue that such generic
> > > compatible should not be used as fallback at all, because it is simply
> > > to generic (PWM is not some model name but common acronym),
> >
> > I suppose dw-apb-timers is the actual document name, but that's already
> > been used for the timer mode in a number of SoCs so probably isn't going
> > to be useful. dw-apb-timers-pwm might be a better prefix if snps,pwm is
> > not going to be acceptable. (Yes, the block can be built as either a
> > PWM or a generic interrupt generating timer at IP generation time)

The first thing I'd like to get sorted is should we rename this to
snps,dw-apb-timers-pwm so we can rename the file and the compatible
that goes with it.

> > As for the version numbers, we could have the -v.vv suffix for these
> > blocks, but the v2.xx log has 22 entries already and only one feature
> > for programming (which is also a configurable one so can't be just
> > enabled by default - it's the 0/100 mode flag in the control registers).
> >
> > I'm not sure what the v1.xx timers had, but I don't have access to this
> > information and we're getting these documents as second-generation so I
> > am not sure if we can get a v1.xx at-all (I suspect this is also going
> > to have a number of revisions and about 1 useful register api change
> > which would be the "new mode" double counter method which we currently
> > rely on having being implicitly enabled by the IP builder (again this
> > feature is still something that can be configured on IP genaration))
>
> But why would you need v1.xx documentation?

I believe the driver should cover a large part of the v1.xx cores
as well, we just don't have any documentation for these to verify
this.

> > Given the configurability of the core, the version numbers might be
> > usable at some point, but it does seem to be a lot of churn for what
> > currently can be described by one boolean for the 0/100 feature that
> > might-be available. Is there a way of saying the compatible string
> > can be dw-apb-timers-pwm-2.[0-9][0-9][a-z] ?
>
> I don't understand why. Aren't you documenting here only v2.13a version?

The document as-such should cover everything I have a log for, we've not
had time to test the extension for 0or100% which was introduced in 2.11a
spec. The earliest history I have is 2.02d. I will go and see if I can
find someone who can go look for anything earlier.

As a note, it does look like all the v2.xx cores have the IP version
register in them so we can auto-detect the version from that, at least
for the DT/platform case.

> Best regards,
> Krzysztof