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Date: Fri, 10 May 2024 12:14:55 +0200
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Subject: Re: [PATCH v2 2/3] dt-bindings: arm: mediatek: mmsys: Add OF graph
 support for board path
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References: <20240409120211.321153-1-angelogioacchino.delregno@collabora.com>
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From: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
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Il 10/05/24 11:34, CK Hu (胡俊光) ha scritto:
> On Thu, 2024-05-09 at 11:27 +0200, AngeloGioacchino Del Regno wrote:
>> Il 09/05/24 07:42, CK Hu (胡俊光) ha scritto:
>>> On Wed, 2024-05-08 at 15:03 +0200, AngeloGioacchino Del Regno
>>> wrote:
>>>> Il 08/05/24 09:19, CK Hu (胡俊光) ha scritto:
>>>>> On Tue, 2024-05-07 at 16:07 +0200, AngeloGioacchino Del Regno
>>>>> wrote:
>>>>>> Il 07/05/24 08:59, CK Hu (胡俊光) ha scritto:
>>>>>>> On Thu, 2024-05-02 at 10:50 +0200, AngeloGioacchino Del
>>>>>>> Regno
>>>>>>> wrote:
>>>>>>>> Il 25/04/24 04:23, CK Hu (胡俊光) ha scritto:
>>>>>>>>> Hi, Angelo:
>>>>>>>>>
>>>>>>>>> On Tue, 2024-04-09 at 14:02 +0200, AngeloGioacchino Del
>>>>>>>>> Regno
>>>>>>>>> wrote:
>>>>>>>>>> Document OF graph on MMSYS/VDOSYS: this supports up
>>>>>>>>>> to
>>>>>>>>>> three
>>>>>>>>>> DDP
>>>>>>>>>> paths
>>>>>>>>>> per HW instance (so potentially up to six displays
>>>>>>>>>> for
>>>>>>>>>> multi-
>>>>>>>>>> vdo
>>>>>>>>>> SoCs).
>>>>>>>>>>
>>>>>>>>>> The MMSYS or VDOSYS is always the first component in
>>>>>>>>>> the
>>>>>>>>>> DDP
>>>>>>>>>> pipeline,
>>>>>>>>>> so it only supports an output port with multiple
>>>>>>>>>> endpoints -
>>>>>>>>>> where
>>>>>>>>>> each
>>>>>>>>>> endpoint defines the starting point for one of the
>>>>>>>>>> (currently
>>>>>>>>>> three)
>>>>>>>>>> possible hardware paths.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: AngeloGioacchino Del Regno <
>>>>>>>>>> angelogioacchino.delregno@collabora.com>
>>>>>>>>>> ---
>>>>>>>>>>       .../bindings/arm/mediatek/mediatek,mmsys.yaml |
>>>>>>>>>> 23
>>>>>>>>>> +++++++++++++++++++
>>>>>>>>>>       1 file changed, 23 insertions(+)
>>>>>>>>>>
>>>>>>>>>> diff --git
>>>>>>>>>> a/Documentation/devicetree/bindings/arm/mediatek/medi
>>>>>>>>>> atek
>>>>>>>>>> ,mms
>>>>>>>>>> ys.y
>>>>>>>>>> aml
>>>>>>>>>> b/Documentation/devicetree/bindings/arm/mediatek/medi
>>>>>>>>>> atek
>>>>>>>>>> ,mms
>>>>>>>>>> ys.y
>>>>>>>>>> aml
>>>>>>>>>> index b3c6888c1457..4e9acd966aa5 100644
>>>>>>>>>> ---
>>>>>>>>>> a/Documentation/devicetree/bindings/arm/mediatek/medi
>>>>>>>>>> atek
>>>>>>>>>> ,mms
>>>>>>>>>> ys.y
>>>>>>>>>> aml
>>>>>>>>>> +++
>>>>>>>>>> b/Documentation/devicetree/bindings/arm/mediatek/medi
>>>>>>>>>> atek
>>>>>>>>>> ,mms
>>>>>>>>>> ys.y
>>>>>>>>>> aml
>>>>>>>>>> @@ -93,6 +93,29 @@ properties:
>>>>>>>>>>         '#reset-cells':
>>>>>>>>>>           const: 1
>>>>>>>>>>       
>>>>>>>>>> +  port:
>>>>>>>>>> +    $ref: /schemas/graph.yaml#/properties/port
>>>>>>>>>> +    description:
>>>>>>>>>> +      Output port node. This port connects the
>>>>>>>>>> MMSYS/VDOSYS
>>>>>>>>>> output
>>>>>>>>>> to
>>>>>>>>>> +      the first component of one display pipeline,
>>>>>>>>>> for
>>>>>>>>>> example
>>>>>>>>>> one
>>>>>>>>>> of
>>>>>>>>>> +      the available OVL or RDMA blocks.
>>>>>>>>>> +      Some MediaTek SoCs support up to three display
>>>>>>>>>> outputs
>>>>>>>>>> per
>>>>>>>>>> MMSYS.
>>>>>>>>>> +    properties:
>>>>>>>>>> +      endpoint@0:
>>>>>>>>>> +        $ref:
>>>>>>>>>> /schemas/graph.yaml#/properties/endpoint
>>>>>>>>>> +        description: Output to the primary display
>>>>>>>>>> pipeline
>>>>>>>>>> +
>>>>>>>>>> +      endpoint@1:
>>>>>>>>>> +        $ref:
>>>>>>>>>> /schemas/graph.yaml#/properties/endpoint
>>>>>>>>>> +        description: Output to the secondary display
>>>>>>>>>> pipeline
>>>>>>>>>> +
>>>>>>>>>> +      endpoint@2:
>>>>>>>>>> +        $ref:
>>>>>>>>>> /schemas/graph.yaml#/properties/endpoint
>>>>>>>>>> +        description: Output to the tertiary display
>>>>>>>>>> pipeline
>>>>>>>>>> +
>>>>>>>>>> +    required:
>>>>>>>>>> +      - endpoint@0
>>>>>>>>>> +
>>>>>>>>>
>>>>>>>>> mmsys/vdosys does not output data to the first
>>>>>>>>> component of
>>>>>>>>> display
>>>>>>>>> pipeline, so this connection looks 'virtual'. Shall we
>>>>>>>>> add
>>>>>>>>> something
>>>>>>>>> virtual in device tree? You add this in order to decide
>>>>>>>>> which
>>>>>>>>> pipeline
>>>>>>>>> is 1st, 2nd, 3rd, but for device it don't care which
>>>>>>>>> one is
>>>>>>>>> first.
>>>>>>>>> In
>>>>>>>>> computer, software could change which display is the
>>>>>>>>> primary
>>>>>>>>> display.
>>>>>>>>> I'm not sure it's good to decide display order in
>>>>>>>>> device
>>>>>>>>> tree?
>>>>>>>>>
>>>>>>>>
>>>>>>>> Devicetree describes hardware, so nothing virtual can be
>>>>>>>> present
>>>>>>>> -
>>>>>>>> and in any case,
>>>>>>>> the primary/secondary/tertiary pipeline is in relation to
>>>>>>>> MM/VDO
>>>>>>>> SYS,
>>>>>>>> not referred
>>>>>>>> to software.
>>>>>>>>
>>>>>>>> Better explaining, the primary pipeline is not
>>>>>>>> necessarily
>>>>>>>> the
>>>>>>>> primary display in
>>>>>>>> DRM terms: that's a concept that is completely detached
>>>>>>>> from
>>>>>>>> the
>>>>>>>> scope of this
>>>>>>>> series and this graph - and it's something that shall be
>>>>>>>> managed
>>>>>>>> solely by the
>>>>>>>> driver (mediatek-drm in this case).
>>>>>>>>
>>>>>>>> Coming back to the connection looking, but *not* being
>>>>>>>> virtual:
>>>>>>>> the
>>>>>>>> sense here is
>>>>>>>> that the MM/VDOSYS blocks are used in the display
>>>>>>>> pipeline to
>>>>>>>> "stitch" together
>>>>>>>> the various display pipeline hardware blocks, or, said
>>>>>>>> differently,
>>>>>>>> setting up the
>>>>>>>> routing between all of those (P.S.:
>>>>>>>> mmsys_mtxxxx_routing_table!)
>>>>>>>> through the VDO
>>>>>>>> Input Selection (VDOx_SEL_IN) or Output Selection
>>>>>>>> (VDOx_SEL_OUT)
>>>>>>>> and
>>>>>>>> with the
>>>>>>>> assistance of the VDO Multiple Output Mask (VDOx_MOUT)
>>>>>>>> for
>>>>>>>> the
>>>>>>>> multiple outputs
>>>>>>>> usecase, both of which, are described by this graph.
>>>>>>>
>>>>>>> I agree this part, but this is related to display device OF
>>>>>>> graph.
>>>>>>> These display device would output video data from one
>>>>>>> device
>>>>>>> and
>>>>>>> input
>>>>>>> to another video device. These video device would not input
>>>>>>> or
>>>>>>> output
>>>>>>> video data to mmsys/vdosys.
>>>>>>>
>>>>>>>>
>>>>>>>> This means that the VDOSYS is really the "master" of the
>>>>>>>> display
>>>>>>>> pipeline since
>>>>>>>> everything gets enabled, mixed and matched from there -
>>>>>>>> and
>>>>>>>> that's in
>>>>>>>> the sense
>>>>>>>> of hardware operation, so we are *really* (and not
>>>>>>>> virtually!)
>>>>>>>> flipping switches.
>>>>>>>
>>>>>>> I agree mmsys/vdosys is master of video pipeline, so let's
>>>>>>> define
>>>>>>> what
>>>>>>> the port in mmsys/vdosys is. If the port means the master
>>>>>>> relationship,
>>>>>>> mmsys/vdosys should output port to every display device. Or
>>>>>>> use
>>>>>>> a
>>>>>>> simply way to show the master relation ship
>>>>>>>
>>>>>>> mmsys-subdev = <&ovl0, &rdma0, &color0, ...>, <&ovl1,
>>>>>>> &rdma1,
>>>>>>> &color1,
>>>>>>> ...>;
>>>>>>>
>>>>>>
>>>>>> There's no need to list all of the VDO0/VDO1/mmsys devices in
>>>>>> one
>>>>>> big
>>>>>> array
>>>>>> property, because the actual possible devices can be defined:
>>>>>>       1. In the bindings; and
>>>>>>       2. In the actual OF graph that we write for each
>>>>>> SoC+board
>>>>>> combination.
>>>>>>
>>>>>> A graph cannot contain a connection to a device that cannot
>>>>>> be
>>>>>> connected to
>>>>>> the previous, so, your "mmsys-subdev" list can be retrieved
>>>>>> by
>>>>>> looking at the
>>>>>> graph:
>>>>>>      - Start from VDO0/1 or MMSYS
>>>>>>      - Walk through (visually, even) OUTPUT ports
>>>>>>        - VDO0 (read output ep) -> ovl0 (read output ep) ->
>>>>>> rdma0
>>>>>> (read
>>>>>> output ep) ->
>>>>>>          color0 (...) -> etc
>>>>>>      - Nothing more - it's all defined there.
>>>>>>
>>>>>>>
>>>>>>> Another problem is how to group display device? If two
>>>>>>> pipeline
>>>>>>> could
>>>>>>> be route to the same display interface, such as
>>>>>>>
>>>>>>> rdma0 -> dsi
>>>>>>> rdma1 -> dsi
>>>>>>>
>>>>>>> Would this be single group?
>>>>>>
>>>>>> There are multiple ways of doing this, but one that comes to
>>>>>> my
>>>>>> mind
>>>>>> right now and
>>>>>> that looks clean as well is the following:
>>>>>>
>>>>>> ovl0@ef01 {
>>>>>>        .....
>>>>>>       ports {
>>>>>>         port@0 {
>>>>>>           reg = <0>;
>>>>>>           ovl0_in: endpoint {
>>>>>>             remote-endpoint = <&vdosys0_out>;
>>>>>>           };
>>>>>>         };
>>>>>
>>>>> I'm not sure how do you define this port from OVL to vdosys. If
>>>>> this
>>>>> port means 'master relationship', others could add port in
>>>>> COLOR to
>>>>> point to vdosys because COLOR and vdosys has the 'master
>>>>> relationship'
>>>>> and I could not reject this. So we need more specific
>>>>> definition of
>>>>> this port.
>>>>
>>>>
>>>>> Only the 'first' device in pipeline could have this port?
>>>>
>>>> Correct. Only the first device in a pipeline - and this is
>>>> actually a
>>>> restriction
>>>> that the generic binding definition of port already gives, in a
>>>> way.
>>>>
>>>>
>>>>> In mt8173, one pipeline is
>>>>>
>>>>> ovl -> color -> aal -> od -> rdma -> ufo -> dsi
>>>>>
>>>>> But rdma has an option to read data from od or directly from
>>>>> DRAM.
>>>>> If
>>>>> from DRAM, the pipeline would be changed to
>>>>>
>>>>> rdma -> ufo -> dsi
>>>>>
>>>>>
>>>>> So it's confused which one is 'first'.
>>>>
>>>> That's why the pipeline is *board-specific* and not soc-generic!
>>>>
>>>> And what you described is *exactly* the reason why I'm adding
>>>> support
>>>> for the
>>>> OF graphs in mediatek-drm: specifying the correct pipeline for
>>>> each
>>>> board as per
>>>> what each board wants to use (said differently: for each board's
>>>> *capabilities*).
>>>>
>>>> So, if on a certain board you want to skip OD, you can hook RDMA
>>>> up
>>>> directly to
>>>> MMSYS/VDOSYS.
>>>>
>>>> In MT8173, one pipeline for one board uses endpoints IN/OUT like
>>>> this:
>>>>
>>>> MMSYS -> OVL -> COLOR -> AAL -> OD -> RDMA -> UFO -> DSI
>>>>
>>>> and for another board, endpoints will be like
>>>>
>>>> MMSYS -> RDMA -> UFO -> DSI
>>>>
>>>> ...which is the exact same as you described, and I think that
>>>> your
>>>> confusion comes
>>>> from the fact that you didn't put MMSYS at the beginning of the
>>>> pipeline :-)
>>>
>>> In one board, both OVL and RDMA could switch dynamically. Because
>>> each
>>> one could be the first in one board, mmsys point to both ovl and
>>> rdma?
>>>
>>
>> No.
>>
>> MMSYS would still point ONLY to OVL, because OVL is the "earliest
>> point"
>> of the pipeline that this one board does support.
>>
>> In that case, RDMA being present at a later point in the pipeline
>> does not
>> matter and does not prevent us from *temporarily* skipping OVL-COLOR-
>> AAL-OD
>> and going MMSYS->RDMA *directly*.
>>
>> Switching dynamically is a driver duty and will be 100% possible (as
>> much
>> as it is right now) to dynamically switch OVL and RDMA as long as
>> both are
>> present in the pipeline.
>>
>> With this exact pipeline:
>>
>> MMSYS -> OVL -> COLOR -> AAL -> OD -> RDMA -> UFO -> DSI
>>
>> the driver _can switch dynamically_ between MMSYS->OVL->...->RDMA and
>> MMSYS->RDMA as the driver itself *is allowed to* temporarily ignore
>> part
>> of the pipeline.
>>
>> Please note that, in case it is needed (trust me on this: it's not
>> needed)
>> a custom property in the endpoint node can always be introduced
>> later, so
>> that you can declare a node like
>>
>>            endpoint@0 {
>>              remote-endpoint = <&ovl0_in>;
>>              mediatek,short-path = <&rdma0_in>;
>>            };
>>
>> ...but again, that's never going to be needed, as the driver already
>> does
>> have knowledge of the fact that RDMA is in the pipeline, so it is
>> possible
>> to simply do a temporary override in the driver.
>>
>> What the OF Graph support does is to build the same arrays, that we
>> currently
>> have hardcoded in mediatek-drm, by reading from device tree.
>>
>> Nothing else and nothing more - for now.
>>
>> Having the OF Graph support makes us able to also add new dual-path
>> support
>> with more complicated connections than the current ones, without any
>> problem
>> and, in many cases, without even modifying the bindings from what I
>> provided
>> in this series.
> 
> OK, please add the information we discussed into binding document to
> prevent anyone misusing this binding.
> 

Sorry CK, but the binding *does* already have this information inside - not
in terms of "phrases", but in terms of restrictions of the binding...

If you want, though, I can add this information in the description of the
commit that is adding this binding, is that okay for you?

Thanks,
Angelo

> Regards,
> CK
> 
>>
>> Cheers,
>> Angelo
>>
>>> Regards,
>>> CK
>>>
>>>>
>>>>
>>>>
>>>>
>>>> In case you need any *temporary override* on any board that
>>>> defines a
>>>> pipeline like
>>>>
>>>> MMSYS -> OVL -> COLOR -> AAL -> OD -> RDMA -> UFO -> DSI
>>>>
>>>> so that the pipeline *temporarily* becomes (for power management,
>>>> or
>>>> for any other
>>>> reason) RDMA -> UFO -> DSI .... that's not a concern: the graph
>>>> is
>>>> present, and it
>>>> is used to tell to the driver what is the regular pipeline to
>>>> use.
>>>> Eventual temporary overrides can be managed transparently inside
>>>> of
>>>> the driver with
>>>> C code and no changes to the devicetree are required.
>>>>
>>>>
>>>>> I don't know how to decide which device could point to
>>>>> mmsys/vdosys. So
>>>>> please give a specific definition.
>>>>>
>>>>
>>>> Nothing points TO mmsys/vdosys. It is mmsys/vdosys pointing to a
>>>> device.
>>>>
>>>> So, mmsys/vdosys must point to the *first device in the
>>>> pipeline*.
>>>>
>>>> Any other doubt?
>>>>
>>>> Cheers,
>>>> Angelo
>>>>
>>>>> Regards,
>>>>> CK
>>>>>
>>>>>>
>>>>>>         port@1 {
>>>>>>           reg = <1>;
>>>>>>           ovl0_out0: endpoint@0 {
>>>>>>             remote-endpoint = <&rdma0_in>;
>>>>>>           };
>>>>>>           ovl0_out1: endpoint@1 {
>>>>>>             remote-endpoint = <&rdma1_in>;
>>>>>>           };
>>>>>>         };
>>>>>>       };
>>>>>> };
>>>>>>
>>>>>> rdma0@1234 {
>>>>>>        .....
>>>>>>       ports {
>>>>>>         port@0 {
>>>>>>           reg = <0>;
>>>>>>           rdma0_in: endpoint {
>>>>>>             remote-endpoint = <&ovl0_out0>; /* assuming ovl0
>>>>>> outputs to
>>>>>> rdma0...*/
>>>>>>           };
>>>>>>         };
>>>>>>         port@1 {
>>>>>>           reg = <1>;
>>>>>>           rdma0_out: endpoint@1 {
>>>>>>             remote-endpoint = <&dsi_dual_intf0_in>;
>>>>>>           };
>>>>>>         };
>>>>>>       };
>>>>>> };
>>>>>>
>>>>>>
>>>>>> rdma1@5678 {
>>>>>>        .....
>>>>>>       ports {
>>>>>>         port@0 {
>>>>>>           reg = <0>;
>>>>>>           rdma1_in: endpoint {
>>>>>>             /* assuming ovl0 outputs to rdma1 as well... can
>>>>>> be
>>>>>> something else. */
>>>>>>             remote-endpoint = <&ovl0_out1>;
>>>>>>           };
>>>>>>         };
>>>>>>         port@1 {
>>>>>>           reg = <1>;
>>>>>>           rdma1_out: endpoint {
>>>>>>             remote-endpoint = <&dsi_dual_intf1_in>;
>>>>>>           };
>>>>>>         };
>>>>>>       };
>>>>>> };
>>>>>>
>>>>>>
>>>>>> dsi@9abcd {
>>>>>>        .....
>>>>>>       ports {
>>>>>>         port@0 {
>>>>>>           reg = <0>;
>>>>>>           /* Where endpoint@0 could be always DSI LEFT CTRL */
>>>>>>           dsi_dual_intf0_in: endpoint@0 {
>>>>>>             remote-endpoint = <&rdma0_out>;
>>>>>>           };
>>>>>>           /* ...and @1 could be always DSI RIGHT CTRL */
>>>>>>           dsi_dual_intf1_in: endpoint@1 {
>>>>>>             remote-endpoint = <&rdma1_out>;
>>>>>>           };
>>>>>>         };
>>>>>>
>>>>>>         port@1 {
>>>>>>           reg = <1>;
>>>>>>           dsi0_out: endpoint {
>>>>>>             remote-endpoint = <&dsi_panel_in>;
>>>>>>           };
>>>>>>         };
>>>>>>       };
>>>>>> };
>>>>>>
>>>>>> ...for a dual-dsi panel, it'd be a similar graph.
>>>>>>
>>>>>> Cheers,
>>>>>> Angelo
>>>>>>
>>>>>>>
>>>>>>> mmsys-subdev = <&rdma0, &rdma1, &dsi>;
>>>>>>>
>>>>>>> Or two group?
>>>>>>>
>>>>>>> mmsys-subdev = <&rdma0, &dsi>, <&rdma1, &dsi>;
>>>>>>>
>>>>>>> I think we should clearly define this.
>>>>>>>
>>>>>>> Regards,
>>>>>>> CK
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> Cheers,
>>>>>>>> Angelo
>>>>>>>>
>>>>>>>>> Regards,
>>>>>>>>> CK
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>       required:
>>>>>>>>>>         - compatible
>>>>>>>>>>         - reg
>>>>>>>>
>>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>
>>>>
>>
>>
>>