linux-kernel - Re: [PATCH 1/4] dt-bindings: display/msm: Redocument the dp-controller for QCS8300

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Message-ID: <d45d9832-31b3-4a23-bcc2-8313d2fccec7@quicinc.com>
Date: Wed, 19 Feb 2025 17:43:07 +0800
From: Yongxing Mou <quic_yongmou@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Krzysztof Kozlowski
	<krzk@...nel.org>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar
	<quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        "Maarten
 Lankhorst" <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard
	<mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Rob Herring
	<robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
	<conor+dt@...nel.org>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>,
        "Bjorn
 Andersson" <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>
CC: <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] dt-bindings: display/msm: Redocument the
 dp-controller for QCS8300



On 2025/2/12 21:44, Konrad Dybcio wrote:
> On 12.02.2025 12:28 PM, Krzysztof Kozlowski wrote:
>> On 12/02/2025 12:13, Yongxing Mou wrote:
>>>
>>>
>>> On 2025/2/12 16:35, Krzysztof Kozlowski wrote:
>>>> On 12/02/2025 08:12, Yongxing Mou wrote:
>>>>> We need to enable mst for qcs8300, dp0 controller will support 2 streams
>>>>> output. So not reuse sm8650 dp controller driver and will add a new driver
>>>>> patch for qcs8300 mst feature. Modify the corresponding dt-bingding file
>>>>> to compatible with the qcs8300-dp.
>>>>>
>>>>> Signed-off-by: Yongxing Mou <quic_yongmou@...cinc.com>
>>>> NAK. You just said qcs8300 is compatible with sm8650. I did not ask
>>>> about drivers, I asked about hardware.
>>>>
>>>> This is messy approach. Describe properly the hardware first, instead of
>>>> sending two conflicting patchsets.
>>>>
>>>> Best regards,
>>>> Krzysztof
>>>
>>> Hi, Krzysztof, thanks for reviewing, i want to explain why i submitted
>>> this patch. Patch
>>> https://lore.kernel.org/all/20250114-dts_qcs8300-v3-1-d114cc5e4af9@quicinc.com/
>>> and
>>> https://lore.kernel.org/all/20250120-mdssdt_qcs8300-v4-2-1687e7842125@quicinc.com/
>>> is the qcs8300 display enablement changes. It base on current linux base
>>> code and it only support SST mode, so in the SST mode, qcs8300 dp
>>> controller driver is quite same with sm8650, struct msm_dp_desc only
>>> have 3 members(io_start, id and wide_bus_supported) and they are same
>>> both in qcs8300 and sm8650, so we reuse it. BTW, for dp phy hardware
>>> version, qcs8300 and sm8650 is different.
>>
>> No. In one patchset you claim hardware is like that, in other patchset
>> you say hardware is different.
>>
>> Sorry, hardware does not change based on your patchsets.
>>
>> Sort out this before posting new versions.
> 
> In other words, fallback compatibles must be chosen with features that
> are present in hardware, but not yet supported upstream in mind.
> 
> It's totally fine (and even preferred/expected) to describe hardware resources
> (such as MST clocks here) when initially creating bindings for a piece of hw,
> even though the drivers don't use them yet at that moment.
> 
> dt-bindings are supposed to give the OS a complete representation of the
> hardware and ideally be immutable (which is a struggle, but we're getting
> better). Driver specifics should not influence your decisions (or at least
> do so very minimally) when adding these.
> 
> Now you're in a """good""" position as the display bindings haven't been merged
> yet, so you can still upload a new patchset where the description is more
> accurate. If it was merged, we'd have to break the ABI or add some crazy
> workarounds..
> 
> Please coalesce this patchset with the "add 8300 display support" one.
> 
> Please also describe all 4 MST clocks and whatever other clocks/resets that
> may be necessary down the line.
>   
> Konrad
Thanks, will update it in this patch "add 8300 display support". Because 
this will depend on this change: 
https://patchwork.freedesktop.org/series/142016/. we will first fix our 
dependecy comments and then repost it.