linux-kernel - Re: [PATCH v3 0/3] Convert Microchip's HLCDC Text based DT bindings to JSON schema

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Date: Fri, 19 Jan 2024 22:33:47 +0100
From: Sam Ravnborg <sam@...nborg.org>
To: Dharma.B@...rochip.com
Cc: Linux4Microchip@...rochip.com, linux-pwm@...r.kernel.org,
	alexandre.belloni@...tlin.com, dri-devel@...ts.freedesktop.org,
	Nicolas.Ferre@...rochip.com, Conor.Dooley@...rochip.com,
	thierry.reding@...il.com, krzysztof.kozlowski+dt@...aro.org,
	claudiu.beznea@...on.dev, airlied@...il.com, lee@...nel.org,
	u.kleine-koenig@...gutronix.de, devicetree@...r.kernel.org,
	conor+dt@...nel.org, tzimmermann@...e.de, mripard@...nel.org,
	robh+dt@...nel.org, linux-arm-kernel@...ts.infradead.org,
	bbrezillon@...nel.org, linux-kernel@...r.kernel.org,
	daniel@...ll.ch
Subject: Re: [PATCH v3 0/3] Convert Microchip's HLCDC Text based DT bindings
 to JSON schema

Hi Dharma,

On Fri, Jan 19, 2024 at 08:41:04AM +0000, Dharma.B@...rochip.com wrote:
> Hi Sam,
> On 19/01/24 1:00 am, Sam Ravnborg wrote:
> > [You don't often get email from sam@...nborg.org. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> > 
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> > 
> > Hi Dharma et al.
> > 
> > On Thu, Jan 18, 2024 at 02:56:09PM +0530, Dharma Balasubiramani wrote:
> >> Converted the text bindings to YAML and validated them individually using following commands
> >>
> >> $ make dt_binding_check DT_SCHEMA_FILES=Documentation/devicetree/bindings/
> >> $ make dtbs_check DT_SCHEMA_FILES=Documentation/devicetree/bindings/
> >>
> >> changelogs are available in respective patches.
> >>
> >> Dharma Balasubiramani (3):
> >>    dt-bindings: display: convert Atmel's HLCDC to DT schema
> >>    dt-bindings: atmel,hlcdc: convert pwm bindings to json-schema
> >>    dt-bindings: mfd: atmel,hlcdc: Convert to DT schema format
> > 
> > I know this is a bit late to ask - sorry in advance.
> > 
> > The binding describes the single IP block as a multi functional device,
> > but it is a single IP block that includes the display controller and a
> > simple pwm that can be used for contrast or backlight.
> yes.
> > 
> > If we ignore the fact that the current drivers for hlcdc uses an mfd
> > abstraction, is this then the optimal way to describe the HW?
> > 
> > 
> > In one of my stale git tree I converted atmel lcdc to DT, and here
> Are you referring the "bindings/display/atmel,lcdc.txt"?
Correct.

> > I used:
> > 
> > +  "#pwm-cells":
> > +    description:
> > +      This PWM chip use the default 3 cells bindings
> > +      defined in ../../pwm/pwm.yaml.
> > +    const: 3
> > +
> > +  clocks:
> > +    maxItems: 2
> > +
> > +  clock-names:
> > +    maxItems: 2
> > +    items:
> > +      - const: lcdc_clk
> > +      - const: hclk
> > 
> > This proved to be a simple way to describe the HW.
> > 
> > To make the DT binding backward compatible you likely need to add a few
> > compatible that otherwise would have been left out - but that should do
> > the trick.
> again you mean the compatibles from atmel,lcdc binding?

If the new binding describes the full IP, as I suggest, then I assume
you need to add the compatible "atmel,hlcdc-pwm" to be backward
compatible. Otherwise users assuming the old binding will fail to find
the pwm info. I am not sure how important this is - but at least then
the device trees can be updated out of sync with the current users.

I hope this explains what I tried to say, otherwise do not hesitate to
get back to me.

	Sam