linux-kernel - Re: [RFC PATCH 1/6] dt-bindings: display: imx: Add EPDC

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Message-ID: <20220214234517.121e1167@aktux>
Date:   Mon, 14 Feb 2022 23:45:17 +0100
From:   Andreas Kemnade <andreas@...nade.info>
To:     Rob Herring <robh@...nel.org>
Cc:     p.zabel@...gutronix.de, airlied@...ux.ie, daniel@...ll.ch,
        shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
        festevam@...il.com, linux-imx@....com,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, alistair@...stair23.me,
        samuel@...lland.org, josua.mayer@....eu,
        letux-kernel@...nphoenux.org
Subject: Re: [RFC PATCH 1/6] dt-bindings: display: imx: Add EPDC

Hi Rob,

On Fri, 11 Feb 2022 09:46:27 -0600
Rob Herring <robh@...nel.org> wrote:

> On Sun, Feb 06, 2022 at 09:00:11AM +0100, Andreas Kemnade wrote:
> > Add a binding for the Electrophoretic Display Controller found at least
> > in the i.MX6.  
> 
> The first version was in i.MX50 (I helped design the register 
> interface). Is that version compatible?
> 
it has some differences, but that could be detected by EPDC_VERSION
register. I do not own such a device, so I cannot fully check. I have
not seen any driver with devicetree for IMX5. For now I am rejecting
anything which has a EPDC version which I cannot check. 

> > The timing subnode is directly here to avoid having display parameters
> > spread all over the plate.
> > 
> > Supplies are organized the same way as in the fbdev driver in the
> > NXP/Freescale kernel forks. The regulators used for that purpose,
> > like the TPS65185, the SY7636A and MAX17135 have typically a single bit to
> > start a bunch of regulators of higher or negative voltage with a
> > well-defined timing. VCOM can be handled separately, but can also be
> > incorporated into that single bit.
> > 
> > Signed-off-by: Andreas Kemnade <andreas@...nade.info>
> > ---
> >  .../bindings/display/imx/fsl,mxc-epdc.yaml    | 159 ++++++++++++++++++
> >  1 file changed, 159 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/display/imx/fsl,mxc-epdc.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/display/imx/fsl,mxc-epdc.yaml b/Documentation/devicetree/bindings/display/imx/fsl,mxc-epdc.yaml
> > new file mode 100644
> > index 000000000000..7e0795cc3f70
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/display/imx/fsl,mxc-epdc.yaml
> > @@ -0,0 +1,159 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/display/imx/fsl,mxc-epdc.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Freescale i.MX6 EPDC
> > +
> > +maintainers:
> > +  - Andreas Kemnade <andreas@...nade.info>
> > +
> > +description: |
> > +  The EPDC is a controller for handling electronic paper displays found in
> > +  i.MX6 SoCs.
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - fsl,imx6sl-epdc
> > +      - fsl,imx6sll-epdc  
> 
> Not compatible with each other?
> 
differences are detectable by EPDC_VERSION register, so probably so
problem. NXP/Freescale kernel uses
fsl,imx6dl-epdc
and 
fsl,imx7d-epdc (used also by imx6 devices with EPDC_VERSION = 3.0)
in their drivers.

fsl,imx6dl-epdc
fsl,imx6sl-epdc
fsl,imx6sll-epdc
fsl,imx7d-epdc
in their dtsis.

But the general rule is to use as less as possible compatible strings
if differences can be probed properly, so only one should be
sufficient? Which one?

Regards,
Andreas