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From:   Guillaume Ranquet <granquet@baylibre.com>
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Date:   Tue, 4 Oct 2022 04:55:07 -0700
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Subject: Re: [PATCH v1 17/17] drm/mediatek: Add mt8195-dpi support to drm_drv
To:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Kishon Vijay Abraham I <kishon@ti.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Vinod Koul <vkoul@kernel.org>, Stephen Boyd <sboyd@kernel.org>,
        David Airlie <airlied@linux.ie>,
        Rob Herring <robh+dt@kernel.org>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Daniel Vetter <daniel@ffwll.ch>,
        Chunfeng Yun <chunfeng.yun@mediatek.com>,
        CK Hu <ck.hu@mediatek.com>, Jitao shi <jitao.shi@mediatek.com>,
        Chun-Kuang Hu <chunkuang.hu@kernel.org>
Cc:     linux-mediatek@lists.infradead.org,
        dri-devel@lists.freedesktop.org,
        Pablo Sun <pablo.sun@mediatek.com>, linux-clk@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Mattijs Korpershoek <mkorpershoek@baylibre.com>,
        linux-arm-kernel@lists.infradead.org,
        linux-phy@lists.infradead.org, devicetree@vger.kernel.org
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On Tue, 04 Oct 2022 12:49, Krzysztof Kozlowski
<krzysztof.kozlowski@linaro.org> wrote:
>On 03/10/2022 17:29, Guillaume Ranquet wrote:
>> On Tue, 27 Sep 2022 16:28, Krzysztof Kozlowski
>> <krzysztof.kozlowski@linaro.org> wrote:
>>> On 27/09/2022 15:04, Guillaume Ranquet wrote:
>>>> On Thu, 22 Sep 2022 09:20, Krzysztof Kozlowski
>>>> <krzysztof.kozlowski@linaro.org> wrote:
>>>>> On 19/09/2022 18:56, Guillaume Ranquet wrote:
>>>>>> Add dpi support to enable the HDMI path.
>>>>>>
>>>>>> Signed-off-by: Guillaume Ranquet <granquet@baylibre.com>
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
>>>>>> index 72049a530ae1..27f029ca760b 100644
>>>>>> --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
>>>>>> +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
>>>>>> @@ -820,6 +820,8 @@ static const struct of_device_id mtk_ddp_comp_dt_ids[] = {
>>>>>>  	  .data = (void *)MTK_DPI },
>>>>>>  	{ .compatible = "mediatek,mt8192-dpi",
>>>>>>  	  .data = (void *)MTK_DPI },
>>>>>> +	{ .compatible = "mediatek,mt8195-dpi",
>>>>>> +	  .data = (void *)MTK_DPI },
>>>>>
>>>>> It's compatible with the others. You don't need more compatibles.
>>>>
>>>> Hi Krzysztof,
>>>>
>>>> It's a bit confusing, because this compatible is used in both
>>>> mtk_drm_drv.c and in mtk_dpi.c
>>>>
>>>> Albeit it's entirely the same thing regarding the mtk_drm_drv module,
>>>> it's pretty different
>>>> regarding the mtk_dpi module.
>>>
>>> Sure, but this does not explain why do you need these entries here in
>>> mtk_drm_drv.
>>>
>>> Best regards,
>>> Krzysztof
>>>
>>
>> Hi Krzysztof,
>>
>> Sorry for the late answer.
>> The mtk_drm_drv is the component master of the full mediatek drm stack.
>>
>> it "binds" all of the crtc/dpi/ovl/mutex/merge... components of the stack.
>>
>> That mtk_ddp_comp_dt_ids array is iterated over to find all of the components
>> from the device tree.
>
>No. You said what the code is doing. I think I understand this. You
>still do not need more compatibles. Your sentence did not clarify it
>because it did not answer at all to question "why". Why do you need it?
>
>Sorry, the change looks not correct.
>
>Best regards,
>Krzysztof
>

I need a new compatible to adress the specifics of mt8195 in the mtk_dpi driver,
the change is in this series with:
[PATCH v1 16/17] drm/mediatek: dpi: Add mt8195 hdmi to DPI driver [1]

I then need to add that compatible to the "list" here in mtk_drm_drv.
I don't see a way around this unless I rewrite the way mtk_drm_drv works?

Maybe if I declare a new compatible that is generic to all mediatek
dpi variants?
and have all the dts specify the node with both the generic dpi and
the specific compatible?

dpi@xxx {
	compatible = "mediatek,dpi", "mediatek,mt8195-dpi";
	...
}

Then I can "collapse" all the dpi related nodes in mtk_drm_drv under
"mediatek,dpi" ?

I guess would have to do the change for all other components that are needed in
mtk_drm_drv (mmsys, aal, ccor, color, dither, dsc, gamma, mutex...).

That's the only trivial way I can think of implementing this with the
current status
of the mtk_drm stack.

Do you have any other ideas in mind?

Thx,
Guillaume.

[1] : https://lore.kernel.org/all/20220919-v1-16-4844816c9808@baylibre.com/