Re: [PATCH v4] drm/mediatek: mtk_dsi: Avoid EPROBE_DEFER loop with external bridge

[CK Hu]

Hi, Angelo:

On Tue, 2022-02-08 at 16:20 +0800, CK Hu wrote:
> Hi, Angelo:
> 
> On Mon, 2022-01-31 at 09:55 +0100, AngeloGioacchino Del Regno wrote:
> > DRM bridge drivers are now attaching their DSI device at probe
> > time,
> > which requires us to register our DSI host in order to let the
> > bridge
> > to probe: this recently started producing an endless -EPROBE_DEFER
> > loop on some machines that are using external bridges, like the
> > parade-ps8640, found on the ACER Chromebook R13.
> > 
> > Now that the DSI hosts/devices probe sequence is documented, we can
> > do adjustments to the mtk_dsi driver as to both fix now and make
> > sure
> > to avoid this situation in the future: for this, following what is
> > documented in drm_bridge.c, move the mtk_dsi component_add() to the
> > mtk_dsi_ops.attach callback and delete it in the detach callback;
> > keeping in mind that we are registering a drm_bridge for our DSI,
> > which is only used/attached if the DSI Host is bound, it wouldn't
> > make sense to keep adding our bridge at probe time (as it would
> > be useless to have it if mtk_dsi_ops.attach() fails!), so also move
> > that one to the dsi host attach function (and remove it in detach).
> > 
> > Cc: <stable@xxxxxxxxxxxxxxx> # 5.15.x
> > Signed-off-by: AngeloGioacchino Del Regno <
> > angelogioacchino.delregno@xxxxxxxxxxxxx>
> > Reviewed-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
> > Reviewed-by: Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx>
> > 
> > ---
> >  drivers/gpu/drm/mediatek/mtk_dsi.c | 167 +++++++++++++++----------
> > ----
> >  1 file changed, 84 insertions(+), 83 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c
> > b/drivers/gpu/drm/mediatek/mtk_dsi.c
> > index 5d90d2eb0019..bced4c7d668e 100644
> > --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> > +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> > @@ -786,18 +786,101 @@ void mtk_dsi_ddp_stop(struct device *dev)
> >  	mtk_dsi_poweroff(dsi);
> >  }
> >  
> > 
> 
> [snip]
> 
> > +
> >  static int mtk_dsi_host_attach(struct mipi_dsi_host *host,
> >  			       struct mipi_dsi_device *device)
> >  {
> >  	struct mtk_dsi *dsi = host_to_dsi(host);
> > +	struct device *dev = host->dev;
> > +	int ret;
> >  
> >  	dsi->lanes = device->lanes;
> >  	dsi->format = device->format;
> >  	dsi->mode_flags = device->mode_flags;
> > +	dsi->next_bridge = devm_drm_of_get_bridge(dev, dev->of_node, 0,
> > 0);
> 
> The original would process panel. Why do you remove the panel part?
> It's better that someone has a platform of DSI->Panel to test this
> patch.

Sorry, devm_drm_of_get_bridge() has processed the panel part, so for
this patch,

Reviewed-by: CK Hu <ck.hu@xxxxxxxxxxxx>

> 
> Regards,
> CK
> 
> > +	if (IS_ERR(dsi->next_bridge))
> > +		return PTR_ERR(dsi->next_bridge);
> > +
> > +	drm_bridge_add(&dsi->bridge);
> > +
> > +	ret = component_add(host->dev, &mtk_dsi_component_ops);
> > +	if (ret) {
> > +		DRM_ERROR("failed to add dsi_host component: %d\n",
> > ret);
> > +		drm_bridge_remove(&dsi->bridge);
> > +		return ret;
> > +	}
> >  
> >  	return 0;
> >  }
> >  
> > +static int mtk_dsi_host_detach(struct mipi_dsi_host *host,
> > +			       struct mipi_dsi_device *device)
> > +{
> > +	struct mtk_dsi *dsi = host_to_dsi(host);
> > +
> > +	component_del(host->dev, &mtk_dsi_component_ops);
> > +	drm_bridge_remove(&dsi->bridge);
> > +	return 0;
> > +}
> > +
> >  static void mtk_dsi_wait_for_idle(struct mtk_dsi *dsi)
> >  {
> >  	int ret;
> > @@ -938,73 +1021,14 @@ static ssize_t mtk_dsi_host_transfer(struct
> > mipi_dsi_host *host,
> >  
> >  static const struct mipi_dsi_host_ops mtk_dsi_ops = {
> >  	.attach = mtk_dsi_host_attach,
> > +	.detach = mtk_dsi_host_detach,
> >  	.transfer = mtk_dsi_host_transfer,
> >  };
> >  
> > 
> 
> [snip]
> 
> > -
> >  static int mtk_dsi_probe(struct platform_device *pdev)
> >  {
> >  	struct mtk_dsi *dsi;
> >  	struct device *dev = &pdev->dev;
> > -	struct drm_panel *panel;
> >  	struct resource *regs;
> >  	int irq_num;
> >  	int ret;
> > @@ -1021,19 +1045,6 @@ static int mtk_dsi_probe(struct
> > platform_device *pdev)
> >  		return ret;
> >  	}
> >  
> > -	ret = drm_of_find_panel_or_bridge(dev->of_node, 0, 0,
> > -					  &panel, &dsi->next_bridge);
> > -	if (ret)
> > -		goto err_unregister_host;
> > -
> > -	if (panel) {
> > -		dsi->next_bridge = devm_drm_panel_bridge_add(dev,
> > panel);
> > -		if (IS_ERR(dsi->next_bridge)) {
> > -			ret = PTR_ERR(dsi->next_bridge);
> > -			goto err_unregister_host;
> > -		}
> > -	}
> > -
> >  	dsi->driver_data = of_device_get_match_data(dev);
> >  
> >  	dsi->engine_clk = devm_clk_get(dev, "engine");
> > @@ -1098,14 +1109,6 @@ static int mtk_dsi_probe(struct
> > platform_device *pdev)
> >  	dsi->bridge.of_node = dev->of_node;
> >  	dsi->bridge.type = DRM_MODE_CONNECTOR_DSI;
> >  
> > -	drm_bridge_add(&dsi->bridge);
> > -
> > -	ret = component_add(&pdev->dev, &mtk_dsi_component_ops);
> > -	if (ret) {
> > -		dev_err(&pdev->dev, "failed to add component: %d\n",
> > ret);
> > -		goto err_unregister_host;
> > -	}
> > -
> >  	return 0;
> >  
> >  err_unregister_host:
> > @@ -1118,8 +1121,6 @@ static int mtk_dsi_remove(struct
> > platform_device *pdev)
> >  	struct mtk_dsi *dsi = platform_get_drvdata(pdev);
> >  
> >  	mtk_output_dsi_disable(dsi);
> > -	drm_bridge_remove(&dsi->bridge);
> > -	component_del(&pdev->dev, &mtk_dsi_component_ops);
> >  	mipi_dsi_host_unregister(&dsi->host);
> >  
> >  	return 0;