linux-kernel - Re: [PATCH v1 17/17] drm/mediatek: Add mt8195-dpi support to drm

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Date:   Tue, 4 Oct 2022 17:05:11 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Guillaume Ranquet <granquet@...libre.com>,
        Michael Turquette <mturquette@...libre.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Vinod Koul <vkoul@...nel.org>, Stephen Boyd <sboyd@...nel.org>,
        David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        CK Hu <ck.hu@...iatek.com>, Jitao shi <jitao.shi@...iatek.com>,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>
Cc:     linux-mediatek@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org,
        Pablo Sun <pablo.sun@...iatek.com>, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Mattijs Korpershoek <mkorpershoek@...libre.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-phy@...ts.infradead.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v1 17/17] drm/mediatek: Add mt8195-dpi support to drm_drv

On 04/10/2022 13:55, Guillaume Ranquet wrote:
>> 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]

But you do not have specifics of mt8195. I wrote it in the beginning.

> 
> I then need to add that compatible to the "list" here in mtk_drm_drv.

No, you do not... I checked the driver and there is no single need... or
convince me you need.

> I don't see a way around this unless I rewrite the way mtk_drm_drv works?

Why rewrite? You have all compatibles in place.

> 
> Maybe if I declare a new compatible that is generic to all mediatek
> dpi variants?

You were asked to use fallback. Don't create some fake fallbacks. Use
existing ones.

> 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";

I don't know what's this but certainly looks odd. Some wild-card
compatible in front (not fallback) and none are documented.

> 	...
> }
> 
> 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?

Use fallback of compatible device. That's the common pattern.
Everywhere, Mediatek as well.

Best regards,
Krzysztof