linux-kernel - Re: [Freedreno] [PATCH v2 2/2] drm/msm/dpu: Add SC8180x to hw catalog

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Date:   Tue, 15 Feb 2022 18:16:45 -0800
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
CC:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        <linux-arm-msm@...r.kernel.org>, <freedreno@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>
Subject: Re: [Freedreno] [PATCH v2 2/2] drm/msm/dpu: Add SC8180x to hw catalog



On 2/15/2022 6:03 PM, Bjorn Andersson wrote:
> On Tue 15 Feb 19:34 CST 2022, Abhinav Kumar wrote:
> 
>>
>>
>> On 2/15/2022 4:20 PM, Dmitry Baryshkov wrote:
>>> On Tue, 15 Feb 2022 at 23:21, Abhinav Kumar <quic_abhinavk@...cinc.com> wrote:
>>>> On 2/15/2022 10:42 AM, Dmitry Baryshkov wrote:
>>>>> On Tue, 15 Feb 2022 at 20:42, Abhinav Kumar <quic_abhinavk@...cinc.com> wrote:
>>>>>> On 2/15/2022 9:28 AM, Bjorn Andersson wrote:
>>>>>>> On Tue 15 Feb 11:14 CST 2022, Abhinav Kumar wrote:
>>>>>>>> On 2/14/2022 8:33 PM, Bjorn Andersson wrote:
>>>>>>>>> From: Rob Clark <robdclark@...omium.org>
> [..]
>>>>> (thus leading us to cases when someone would forget to add INTF_EDP
>>>>> next to INTF_DP)
>>>>>
>>>>> Also, if we are switching from INTF_DP to INTF_EDP, should we stop
>>>>> using end-to-end numbering (like MSM_DP_CONTROLLER_2 for INTF_5) and
>>>>> add a separate numbering scheme for INTF_EDP?
>>>>>
>>>> We should change the controller ID to match what it actually is.
>>>>
>>>> Now that you pointed this out, this looks even more confusing to me to
>>>> say that  MSM_DP_CONTROLLER_2 is actually a EDP controller because
>>>> fundamentally and even hardware block wise they are different.
>>>
>>> So, do we split msm_priv->dp too? It's indexed using
>>> MSM_DP_CONTROLLER_n entries.
>>> Do we want to teach drm/msm/dp code that there are priv->dp[] and
>>> priv->edp arrays?
>>
>> ok so now priv->dp and priv->edp arrays are also in the picture here :)
>>
>> Actually all these questions should have probably come when we were figuring
>> out how best to re-use eDP and DP driver.
>>
>> Either way atleast, its good we are documenting all these questions on this
>> thread so that anyone can refer this to know what all was missed out :)
>>
>> priv->dp is of type msm_dp. When re-using DP driver for eDP and since
>> struct msm_dp is the shared struct between dpu and the msm/dp, I get your
>> point of re-using MSM_DP_CONTROLLER_* as thats being use to index.
>>
>> So MSM_DP_CONTROLLER_* is more of an index into the DP driver and not really
>> a hardware indexing scheme.
>>
>> If we split into two arrays, we need more changes to dpu_encoder too.
>>
>> Too instrusive a change at this point, even though probably correct.
>>
> 
> I'm sorry, but performing such a split would create a whole bunch of
> duplication and I don't see the reasons yet. Can you please give me an
> example of when the DPU _code_ would benefit from being specifically
> written for EDP vs DP?
> 
> Things where it doesn't make sense to enable certain features in
> runtime - but really have different implementation for the two interface
> types.
> 

Like I have mentioned in my previous comment, this would be a big change 
and I am also not in favor of this big change.

>> But are you seeing more changes required even if we just change INTF_DP to
>> INTF_eDP for the eDP entries? What are the challenges there?
>>
> 
> What are the benefits?

In terms of current code, again like I said before in my previous 
comments several times I do not have an example.

I was keeping the separation in case in future for some features we do 
need to differentiate eDP and DP.

Somehow I also feel this change and below are interlinked that way.

https://patchwork.freedesktop.org/patch/473871/

The only reason we need this change is because both eDP and DP use 
DRM_MODE_ENCODER_TMDS and specifying the intf_type directly will clear 
the confusion because DRM_MODE_ENCODER_DSI means DSI and 
DRM_MODE_ENCODER_VIRTUAL means Writeback but DRM_MODE_ENCODER_TMDS can 
mean DP OR eDP interface.

The ambiguity was always for eDP and DP.

That led to the discussion about the INTF_* we are specifying in the 
dpu_hw_catalog only to find the discrepancy.

So now by clearing that ambiguity that change makes sense. That 
discussion trickled into this one.

> 
> Regards,
> Bjorn