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

[Alexandre Mergnat]

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