linux-kernel - Re: [PATCH 1/3] drm/msm/dpu: Add DPU_INTF_DATABUS

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Message-ID: <e23de804-060d-3278-5045-1ed03f0de80d@quicinc.com>
Date:   Wed, 14 Jun 2023 12:35:09 -0700
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC:     Jessica Zhang <quic_jesszhan@...cinc.com>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] drm/msm/dpu: Add DPU_INTF_DATABUS_WIDEN feature flag
 for DPU >= 5.0



On 6/14/2023 5:23 AM, Marijn Suijten wrote:
> On 2023-06-14 15:01:59, Dmitry Baryshkov wrote:
>> On 14/06/2023 14:42, Marijn Suijten wrote:
>>> On 2023-06-13 18:57:11, Jessica Zhang wrote:
>>>> DPU 5.x+ supports a databus widen mode that allows more data to be sent
>>>> per pclk. Enable this feature flag on all relevant chipsets.
>>>>
>>>> Signed-off-by: Jessica Zhang <quic_jesszhan@...cinc.com>
>>>> ---
>>>>    drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.c | 3 ++-
>>>>    drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h | 2 ++
>>>>    2 files changed, 4 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.c
>>>> index 36ba3f58dcdf..0be7bf0bfc41 100644
>>>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.c
>>>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.c
>>>> @@ -103,7 +103,8 @@
>>>>    	(BIT(DPU_INTF_INPUT_CTRL) | \
>>>>    	 BIT(DPU_INTF_TE) | \
>>>>    	 BIT(DPU_INTF_STATUS_SUPPORTED) | \
>>>> -	 BIT(DPU_DATA_HCTL_EN))
>>>> +	 BIT(DPU_DATA_HCTL_EN) | \
>>>> +	 BIT(DPU_INTF_DATABUS_WIDEN))
>>>
>>> This doesn't work.  DPU 5.0.0 is SM8150, which has DSI 6G 2.3.  In the
>>> last patch for DSI you state and enable widebus for DSI 6G 2.5+ only,
>>> meaning DPU and DSI are now desynced, and the output is completely
>>> corrupted.
> 
> Tested this on SM8350 which actually has DSI 2.5, and it is also
> corrupted with this series so something else on this series might be
> broken.
> 
>>> Is the bound in dsi_host wrong, or do DPU and DSI need to communicate
>>> when widebus will be enabled, based on DPU && DSI supporting it?
>>
>> I'd prefer to follow the second approach, as we did for DP. DPU asks the
>> actual video output driver if widebus is to be enabled.
> 

I was afraid of this. This series was made on an assumption that the DPU 
version of widebus and DSI version of widebus would be compatible but 
looks like already SM8150 is an outlier.

Yes, I think we have to go with second approach.

DPU queries DSI if it supports widebus and enables it.

Thanks for your responses. We will post a v2.

> Doesn't it seem very strange that DPU 5.x+ comes with a widebus feature,
> but the DSI does not until two revisions later?  Or is this available on
> every interface, but only for a different (probably DP) encoder block?
> 

Yes its strange.

> - Marijn