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Date:   Fri, 24 Jun 2022 15:53:45 -0700
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Subject: Re: [PATCH v1 2/3] drm/msm/dp: decoupling dp->id out of dp
 controller_id at scxxxx_dp_cfg table
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To:     Stephen Boyd <swboyd@chromium.org>, <agross@kernel.org>,
        <airlied@linux.ie>, <bjorn.andersson@linaro.org>,
        <daniel@ffwll.ch>, <dianders@chromium.org>,
        <dmitry.baryshkov@linaro.org>, <dri-devel@lists.freedesktop.org>,
        <robdclark@gmail.com>, <sean@poorly.run>, <vkoul@kernel.org>
CC:     <quic_abhinavk@quicinc.com>, <quic_aravindh@quicinc.com>,
        <quic_sbillaka@quicinc.com>, <freedreno@lists.freedesktop.org>,
        <linux-arm-msm@vger.kernel.org>, <linux-kernel@vger.kernel.org>
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From:   Kuogee Hsieh <quic_khsieh@quicinc.com>
In-Reply-To: <CAE-0n51g-EVsC-i9=sJV-ySa8VnE+yT7cg=b-TNMi9+3uBiOVA@mail.gmail.com>
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On 6/24/2022 3:19 PM, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2022-06-24 14:49:57)
>> On 6/24/2022 2:40 PM, Stephen Boyd wrote:
>>> Quoting Kuogee Hsieh (2022-06-24 14:17:50)
>>>> On 6/24/2022 1:00 PM, Stephen Boyd wrote:
>>>>> Quoting Kuogee Hsieh (2022-06-24 10:15:11)
>>>>>> Current the index (dp->id) of DP descriptor table (scxxxx_dp_cfg[]) are tightly
>>>>>> coupled with DP controller_id. This means DP use controller id 0 must be placed
>>>>>> at first entry of DP descriptor table (scxxxx_dp_cfg[]). Otherwise the internal
>>>>>> INTF will mismatch controller_id. This will cause controller kickoff wrong
>>>>>> interface timing engine and cause dpu_encoder_phys_vid_wait_for_commit_done
>>>>>> vblank timeout error.
>>>>>>
>>>>>> This patch add controller_id field into struct msm_dp_desc to break the tightly
>>>>>> coupled relationship between index (dp->id) of DP descriptor table with DP
>>>>>> controller_id.
>>>>> Please no. This reverts the intention of commit bb3de286d992
>>>>> ("drm/msm/dp: Support up to 3 DP controllers")
>>>>>
>>>>>        A new enum is introduced to document the connection between the
>>>>>        instances referenced in the dpu_intf_cfg array and the controllers in
>>>>>        the DP driver and sc7180 is updated.
>>>>>
>>>>> It sounds like the intent of that commit failed to make a strong enough
>>>>> connection. Now it needs to match the INTF number as well? I can't
>>>>> really figure out what is actually wrong, because this patch undoes that
>>>>> intentional tight coupling. Is the next patch the important part that
>>>>> flips the order of the two interfaces?
>>>> The commit bb3de286d992have two problems,
>>>>
>>>> 1)  The below sc7280_dp_cfg will not work, if eDP use
>>>> MSM_DP_CONTROLLER_2 instead of  MSM_DP_CONTROLLER_1
>>> Why would we use three indices for an soc that only has two indices
>>> possible? This is not a real problem?
>> I do not what will happen at future, it may have more dp controller use
>> late.
>>
>> at current soc, below table has only one eDP will not work either.
>>
>> static const struct msm_dp_config sc7280_dp_cfg = {
>>            .descs = (const struct msm_dp_desc[]) {
>>                    [MSM_DP_CONTROLLER_1] = { .io_start = 0x0aea0000,
>> .connector_type = DRM_MODE_CONNECTOR_eDP, .wide_bus_en = true },
>>
>>            .num_descs = 1,
> So the MSM_DP_CONTROLLER_* number needs to match what exactly?MSM

MSM_DP_CONTROLLER_1 need to match to the index = 1 of sc7280_dp_cfg[] <== This is correct

The problem is sc7280_dp_cfg[] have two entries since eDP place at index 
of MSM_DP_CONTROLLER_1.

but .num_desc = 1  <== this said only have one entry at sc7280_dp_cfg[] 
table. Therefore eDP will never be found at for loop  at 
_dpu_kms_initialize_displayport().


>
>>>> since it have num_descs =2 but eDP is at index 2 (CONTROLLER_2) which
>>>> never be reached.
>>>>
>>>> static const struct msm_dp_config sc7280_dp_cfg = {
>>>>            .descs = (const struct msm_dp_desc[]) {
>>>>                    [MSM_DP_CONTROLLER_2] = { .io_start = 0x0aea0000,
>>>> .connector_type = DRM_MODE_CONNECTOR_eDP, .wide_bus_en = true },
>>>>                    [MSM_DP_CONTROLLER_0] = { .io_start = 0x0ae90000,
>>>> .connector_type = DRM_MODE_CONNECTOR_DisplayPort, .wide_bus_en = true },
>>>>            },
>>>>            .num_descs = 2,
>>>> };
>>>>
>>>> 2)  DP always has index of 0 (dp->id = 0) and the first one to call
>>>> msm_dp_modeset_init(). This make DP always place at head of bridge chain.
>>> What does this mean? Are you talking about the list of bridges in drm
>>> core, i.e. 'bridge_list'?
>> yes,
> I changed the drm_bridge_add() API and that doesn't make any difference.
> The corruption is still seen. That would imply it is not the order of
> the list of bridges.

Sorry, my mistake. it is not in drm_bridge_add.

It should be in dpu_encoder_init() of _dpu_kms_initialize_displayport().

can you make below changes (patch) to _dpu_kms_initialize_displayport().

kuogee: go backward for dp modeset_init

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c 
b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
index 3a4da0d..b271a4b 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
@@ -611,9 +611,15 @@ static int _dpu_kms_initialize_displayport(struct 
drm_device *dev,
         struct drm_encoder *encoder = NULL;
         struct msm_display_info info;
         int rc;
-       int i;
+       int i,num;
+
+       num = ARRAY_SIZE(priv->dp);

+#ifdef XXXX
         for (i = 0; i < ARRAY_SIZE(priv->dp); i++) {
+#else
+       for (i = num - 1; i >= 0 ; i--) {
+#endif
                 if (!priv->dp[i])
                         continue;


>
> ---8<---
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index e275b4ca344b..e3518101b65e 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -165,7 +165,7 @@ void drm_bridge_add(struct drm_bridge *bridge)
>   	mutex_init(&bridge->hpd_mutex);
>
>   	mutex_lock(&bridge_lock);
> -	list_add_tail(&bridge->list, &bridge_list);
> +	list_add(&bridge->list, &bridge_list);
>   	mutex_unlock(&bridge_lock);
>   }
>   EXPORT_SYMBOL(drm_bridge_add);
>
>>>> At next patch eDP must be placed at head of bridge chain to fix eDP
>>>> corruption issue. This is the purpose of this patch. I will revise the
>>>> commit text.
>>>>
>>> Wouldn't that be "broken" again if we decided to change drm_bridge_add()
>>> to add to the list head instead of list tail? Or if somehow
>>> msm_dp_modeset_init() was called in a different order so that the DP
>>> bridge was added before the eDP bridge?
>> we have no control of drm_bridge_add().
>>
>> Since drm perform screen update following bridge chain sequentially, we
>> have to make sure primary always update first.
>>