linux-kernel - Re: [PATCH v7 2/6] drm/mediatek: dsi: Improves the DSI lane setup robustness

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Message-ID: <0863ee2e-25ed-43b7-a896-e380de828d58@baylibre.com>
Date: Wed, 26 Feb 2025 12:35:42 +0100
From: Alexandre Mergnat <amergnat@...libre.com>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 CK Hu (胡俊光) <ck.hu@...iatek.com>
Cc: "maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>,
 "mripard@...nel.org" <mripard@...nel.org>,
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 Jitao Shi (石记涛) <jitao.shi@...iatek.com>,
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Subject: Re: [PATCH v7 2/6] drm/mediatek: dsi: Improves the DSI lane setup
 robustness



On 18/02/2025 09:52, AngeloGioacchino Del Regno wrote:
> Il 17/02/25 16:03, Alexandre Mergnat ha scritto:
>> Hi CK.
>>
>> On 17/02/2025 08:56, CK Hu (胡俊光) wrote:
>>> On Fri, 2025-01-10 at 14:31 +0100, Alexandre Mergnat wrote:
>>>> External email : Please do not click links or open attachments until you have verified the 
>>>> sender or the content.
>>>>
>>>>
>>>> Currently, mtk_dsi_lane_ready (which setup the DSI lane) is triggered
>>>> before mtk_dsi_poweron. lanes_ready flag toggle to true during
>>>> mtk_dsi_lane_ready function, and the DSI module is set up during
>>>> mtk_dsi_poweron.
>>>>
>>>> Later, during panel driver init, mtk_dsi_lane_ready is triggered but does
>>>> nothing because lanes are considered ready. Unfortunately, when the panel
>>>> driver try to communicate, the DSI returns a timeout.
>>>>
>>>> The solution found here is to put lanes_ready flag to false after the DSI
>>>> module setup into mtk_dsi_poweron to init the DSI lanes after the power /
>>>> setup of the DSI module.
>>>
>>> I'm not clear about what happen.
>>> I think this DSI flow has worked for a long time.
>>> So only some panel has problem?
>>
>> I don't know if it's related to a specific panel or not.
>>
>>>
>>> And another question.
>>> Do you mean mtk_dsi_lane_ready() do some setting to hardware, but lane is not actually ready?
>>
>> The workflow should be:
>> ... | dsi->lanes_ready = false | Power-on | setup dsi lanes | dsi->lanes_ready = true (to avoid 
>> re-do dsi lanes setup) | ...
>>
>> I observe (print function name called + dsi->lanes_ready value):
> 
> Alex, the first poweron is called by mtk_dsi_ddp_start() - and the start callback
> is internal to the mediatek-drm driver.
> 
> That callback is called by mtk_crtc during setup and during bridge enable(), and
> there we go with suboptimal code design backfiring - instead of using what the
> DRM APIs provide, this driver uses something custom *and* the DRM APIs, giving
> this issue.
> 
> Part of what mtk_crtc does is duplicated with what the DRM APIs want to do, so
> there you go, that's your problem here :-)
> 
> Should I go on with describing the next step(s), or is that obvious for everyone?
> 
> :-)
> 
> Cheers,

Ok thanks Angelo.
Can you let me know if you agree with this change please ? This should be better:

@@ -843,25 +843,6 @@ static void mtk_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
  	mtk_output_dsi_enable(dsi);
  }

-static void mtk_dsi_bridge_atomic_pre_enable(struct drm_bridge *bridge,
-					     struct drm_bridge_state *old_bridge_state)
-{
-	struct mtk_dsi *dsi = bridge_to_dsi(bridge);
-	int ret;
-
-	ret = mtk_dsi_poweron(dsi);
-	if (ret < 0)
-		DRM_ERROR("failed to power on dsi\n");
-}
-
-static void mtk_dsi_bridge_atomic_post_disable(struct drm_bridge *bridge,
-					       struct drm_bridge_state *old_bridge_state)
-{
-	struct mtk_dsi *dsi = bridge_to_dsi(bridge);
-
-	mtk_dsi_poweroff(dsi);
-}
-
  static enum drm_mode_status
  mtk_dsi_bridge_mode_valid(struct drm_bridge *bridge,
  			  const struct drm_display_info *info,
@@ -886,8 +867,6 @@ static const struct drm_bridge_funcs mtk_dsi_bridge_funcs = {
  	.atomic_disable = mtk_dsi_bridge_atomic_disable,
  	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
  	.atomic_enable = mtk_dsi_bridge_atomic_enable,
-	.atomic_pre_enable = mtk_dsi_bridge_atomic_pre_enable,
-	.atomic_post_disable = mtk_dsi_bridge_atomic_post_disable,
  	.atomic_reset = drm_atomic_helper_bridge_reset,
  	.mode_valid = mtk_dsi_bridge_mode_valid,
  	.mode_set = mtk_dsi_bridge_mode_set,


-- 
Regards,
Alexandre