Re: [RFC PATCH 3/3] dt-bindings: display: add Amlogic Meson DRM Bindings

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Neil,

On Monday 28 Nov 2016 10:23:43 Neil Armstrong wrote:
> On 11/28/2016 09:33 AM, Laurent Pinchart wrote:
> > On Friday 25 Nov 2016 17:03:11 Neil Armstrong wrote:
> >> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
> >> ---
> >> 
> >>  .../bindings/display/meson/meson-drm.txt           | 134 +++++++++++++++
> >>  1 file changed, 134 insertions(+)
> >>  create mode 100644
> >> 
> >> Documentation/devicetree/bindings/display/meson/meson-drm.txt
> >> 
> >> diff --git
> >> a/Documentation/devicetree/bindings/display/meson/meson-drm.txt
> >> b/Documentation/devicetree/bindings/display/meson/meson-drm.txt new file
> >> mode 100644
> >> index 0000000..89c1b5f
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/display/meson/meson-drm.txt
> >> @@ -0,0 +1,134 @@
> >> +Amlogic Meson Display Controller
> >> +================================
> >> +
> >> +The Amlogic Meson Display controller is composed of several components
> >> +that are going to be documented below:
> >> +
> >> +DMC|---------------VPU (Video Processing Unit)------------|------
> >> HHI------|
> >> +   | vd1   _______     _____________    _____________     |              
> >> |
> >> +D  |-------|      |----|            |   |            |    |   HDMI PLL   
> >> |
> >> +D  | vd2   | VIU  |    | Video Post |   | Video Encs |<---|-----VCLK     
> >> |
> >> +R  |-------|      |----| Processing |   |            |    |              
> >> |
> >> +   | osd2  |      |    |            |---| Enci ------|----|-----
> >> VDAC------|
> >> +R  |-------| CSC  |----| Scalers    |   | Encp ------|----|----HDMI-
> >> TX----|
> >> +A  | osd1  |      |    | Blenders   |   |
> >> Encl-------|----|---------------|
> >> +M  |-------|______|----|____________|   |____________|    |              
> >> |
> >> +___|______________________________________________________|____________
> >> ___|
> >> +
> >> +
> >> +VIU: Video Input Unit
> >> +---------------------
> >> +
> >> +The Video Input Unit is in charge of the pixel scanout from the DDR
> >> memory.
> >> +It fetches the frames addresses, stride and parameters from the "Canvas"
> >> memory.
> >> +This part is also in charge of the CSC (Colorspace Conversion).
> >> +It can handle 2 OSD Planes and 2 Video Planes.
> >> +
> >> +VPP: Video Processing Unit
> > 
> > Do you mean "Video Post Processing" ? In your diagram above Video
> > Processing Unit is abbreviated VPU and covers the VIU, VPP and encoders.
> 
> Exact, I meant VPP here.
> 
> >> +--------------------------
> >> +
> >> +The Video Processing Unit is in charge if the scaling and blending of
> >> the
> >> +various planes into a single pixel stream.
> >> +There is a special "pre-blending" used by the video planes with a
> >> dedicated 
> >> +scaler and a "post-blending" to merge with the OSD Planes.
> >> +The OSD planes also have a dedicated scaler for one of the OSD.
> >> +
> >> +VENC: Video Encoders
> >> +--------------------
> >> +
> >> +The VENC is composed of the multiple pixel encoders :
> >> + - ENCI : Interlace Video encoder for CVBS and Interlace HDMI
> >> + - ENCP : Progressive Video Encoder for HDMI
> >> + - ENCL : LCD LVDS Encoder
> >> +The VENC Unit gets a Pixel Clocks (VCLK) from a dedicated HDMI PLL and
> >> clock
> >> +tree and provides the scanout clock to the VPP and VIU.
> >> +The ENCI is connected to a single VDAC for Composite Output.
> >> +The ENCI and ENCP are connected to an on-chip HDMI Transceiver.
> >> +
> >> +Device Tree Bindings:
> >> +---------------------
> >> +
> >> +VPU: Video Processing Unit
> >> +--------------------------
> >> +
> >> +Required properties:
> >> + - compatible: value should be different for each SoC family as :
> >> + 	- GXBB (S905) : "amlogic,meson-gxbb-vpu"
> >> + 	- GXL (S905X, S905D) : "amlogic,meson-gxl-vpu"
> >> + 	- GXM (S912) : "amlogic,meson-gxm-vpu"
> >> +	followed by the common "amlogic,meson-gx-vpu"
> >> + - reg: base address and size of he following memory-mapped regions :
> >> +	- vpu
> >> +	- hhi
> >> +	- dmc
> >> + - reg-names: should contain the names of the previous memory regions
> >> + - interrupts: should contain the VENC Vsync interrupt number
> >> +
> >> +- ports: A ports node with endpoint definitions as defined in
> >> +  Documentation/devicetree/bindings/media/video-interfaces.txt. The
> >> +  second port should be the output endpoints for VENC connectors.
> >> +
> >> +VENC CBVS Output
> >> +----------------------
> >> +
> >> +The VENC can output Composite/CVBS output via a decicated VDAC.
> >> +
> >> +Required properties:
> >> +  - compatible: value must be one of:
> >> + - compatible: value should be different for each SoC family as :
> > One of those two lines is redundant.
> 
> Will fix.
> 
> >> + 	- GXBB (S905) : "amlogic,meson-gxbb-venc-cvbs"
> >> + 	- GXL (S905X, S905D) : "amlogic,meson-gxl-venc-cvbs"
> >> + 	- GXM (S912) : "amlogic,meson-gxm-venc-cvbs"
> >> +	followed by the common "amlogic,meson-gx-venc-cvbs"
> >> +
> > 
> > No registers ? Are the encoders registers part of the VPU register space,
> > intertwined in a way that they can't be specified separately here ?
> 
> Exact, all the video registers on the Amlogic SoC are part of a long history
> of fixup/enhance from very old SoCs, it's quite hard to distinguish a Venc
> registers array since they are mixed with the multiple encoders
> registers...

In that case is there really a reason to model the encoders as separate nodes 
in DT ?

> The only separate registers are the VDAC and HDMI PHY, I may move them to
> these separate nodes since they are part of the HHI register space.
> 
> It is a problem if I move them in the next release ? Next release will
> certainly have HDMI support, and will have these refactorings.

Given that DT bindings are considered as a stable ABI, I'm afraid it's an 
issue.

> >> +- ports: A ports node with endpoint definitions as defined in
> >> +  Documentation/devicetree/bindings/media/video-interfaces.txt. The
> >> +  first port should be the input endpoints, connected ot the VPU node.
> >> +
> >> +Example:
> >> +
> >> +venc_cvbs: venc-cvbs {
> >> +	compatible = "amlogic,meson-gxbb-venc-cvbs";
> >> +	status = "okay";
> >> +
> >> +	ports {
> >> +		#address-cells = <1>;
> >> +		#size-cells = <0>;
> >> +
> >> +		enc_cvbs_in: port@0 {
> >> +			 #address-cells = <1>;
> >> +			 #size-cells = <0>;
> >> +			 reg = <0>;
> >> +
> >> +			 venc_cvbs_in_vpu: endpoint@0 {
> >> +				 reg = <0>;
> >> +				 remote-endpoint = <&vpu_out_venc_cvbs>;
> >> +			};
> >> +		};
> >> +	};
> >> +};
> >> +
> >> +vpu: vpu@d0100000 {
> >> +	compatible = "amlogic,meson-gxbb-vpu";
> >> +	reg = <0x0 0xd0100000 0x0 0x100000>,
> >> +	      <0x0 0xc883c000 0x0 0x1000>,
> >> +	      <0x0 0xc8838000 0x0 0x1000>;
> >> +	reg-names = "base", "hhi", "dmc";
> >> +	interrupts = <GIC_SPI 3 IRQ_TYPE_EDGE_RISING>;
> >> +
> >> +	ports {
> >> +		#address-cells = <1>;
> >> +		#size-cells = <0>;
> >> +
> >> +		vpu_out: port@1 {
> >> +			 #address-cells = <1>;
> >> +			 #size-cells = <0>;
> >> +			 reg = <1>;
> >> +
> >> +			 vpu_out_venc_cvbs: endpoint@0 {
> >> +				 reg = <0>;
> >> +				 remote-endpoint = <&venc_cvbs_in_vpu>;
> >> +			 };
> >> +		 };
> >> +	};
> >> +};
> 
> Thanks for the review !

-- 
Regards,

Laurent Pinchart