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

[CK Hu <ck.hu@mediatek.com>]

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@vger.kernel.org> # 5.15.x
> Signed-off-by: AngeloGioacchino Del Regno <
> angelogioacchino.delregno@collabora.com>
> Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
> Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
> 
> ---
>  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.

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;