linux-kernel - Re: [RFC resend 1/4] dt-bindings: display: mediatek: add drm binding

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Date:   Thu, 19 Oct 2017 15:06:37 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     ulrich.hecht+renesas@...il.com, ck.hu@...iatek.com,
        airlied@...ux.ie, robh+dt@...nel.org, mark.rutland@....com,
        linux@...linux.org.uk, catalin.marinas@....com,
        will.deacon@....com, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Matthias Brugger <mbrugger@...e.com>
Subject: Re: [RFC resend 1/4] dt-bindings: display: mediatek: add drm binding

On Thu, 2017-10-19 at 15:53 +0300, Laurent Pinchart wrote:
> Hi Matthias,
> 
> Thank you for the patch.
> 
> On Thursday, 19 October 2017 14:26:07 EEST Matthias Brugger wrote:
> > DRM subysystem and clock driver shared the same compatible mmsys.
> > This stopped does not work, as only the first driver for a compatible
> > gets probed. We change the comaptible to the new DRM identifier to fix
> > this.
> > 
> > Signed-off-by: Matthias Brugger <mbrugger@...e.com>
> > ---
> >  .../devicetree/bindings/display/mediatek/mediatek,disp.txt          | 6 +++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git
> > a/Documentation/devicetree/bindings/display/mediatek/mediatek,disp.txt
> > b/Documentation/devicetree/bindings/display/mediatek/mediatek,disp.txt
> > index 383183a89164..6db652463e64 100644
> > --- a/Documentation/devicetree/bindings/display/mediatek/mediatek,disp.txt
> > +++ b/Documentation/devicetree/bindings/display/mediatek/mediatek,disp.txt
> > @@ -27,6 +27,7 @@
> > Documentation/devicetree/bindings/display/mediatek/mediatek,dpi.txt.
> > 
> >  Required properties (all function blocks):
> >  - compatible: "mediatek,<chip>-disp-<function>", one of
> > +	"mediatek,<chip>-dispsys"    - central component for the DRM system
> >  	"mediatek,<chip>-disp-ovl"   - overlay (4 layers, blending, csc)
> >  	"mediatek,<chip>-disp-rdma"  - read DMA / line buffer
> >  	"mediatek,<chip>-disp-wdma"  - write DMA
> > @@ -71,6 +72,11 @@ mmsys: clock-controller@...00000 {
> >  	#clock-cells = <1>;
> >  };
> > 
> > +dispsys: display-system {
> > +	compatible = "mediatek,mt2701-dispsys";
> > +	mediatek,mmsys = <&mmsys>;
> > +}
> 
> So this node doesn't correspond to an IP core but is meant as a top-level 
> entry point for the operating system. This leads me to three questions.
> 
> 1. Is there any IP core in the Mediatek display subsystem that could be 
> considered (or at least used) as a top-level entry point ? That would be my 
> preferred solution as I'm not fond of DT nodes not describing hardware.

At least on MT8173 that node is MMSYS, which it is currently matching
against. The issue, if I understand correctly, is that the clocks
provided by this same region were previously created via CLK_OF_DECLARE,
and are now changed to a separate clock driver that matches to the same 
node.

> 2. If there's no such IP core, are all the display subsystem IP cores grouped 
> together in one MMIO register range ? If so we could move them as children of 
> this new display system node which, even if doesn't describe an IP core, would 
> describe the way the display IP cores are grouped in the hardware, and would 
> thus be a hardware description.
> 
> 3. If the answer to the second question is also negative, shouldn't this 
> display system node reference all other display IP DT nodes (through direct 
> phandles and/or OF graph bindings) ?
> 
> >  ovl0: ovl@...0c000 {
> >  	compatible = "mediatek,mt8173-disp-ovl";
> >  	reg = <0 0x1400c000 0 0x1000>;
> 

regards
Philipp