Message-ID: <2c69d44c-5e33-03d3-d981-425ee2167cf9@intel.com>
Date:   Tue, 4 Jan 2022 10:52:56 +0100
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Subject: Re: [PATCH] drm/mediatek: mtk_dsi: Avoid EPROBE_DEFER loop with
 external bridge
Content-Language: en-US
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        <dri-devel@lists.freedesktop.org>
CC:     <chunkuang.hu@kernel.org>, <airlied@linux.ie>,
        <linux-kernel@vger.kernel.org>,
        <linux-mediatek@lists.infradead.org>, <matthias.bgg@gmail.com>,
        <kernel@collabora.com>, <linux-arm-kernel@lists.infradead.org>
References: <20211210113617.196204-1-angelogioacchino.delregno@collabora.com>
From:   Andrzej Hajda <andrzej.hajda@intel.com>
Organization: Intel Technology Poland sp. z o.o. - ul. Slowackiego 173, 80-298
 Gdansk - KRS 101882 - NIP 957-07-52-316
In-Reply-To: <20211210113617.196204-1-angelogioacchino.delregno@collabora.com>
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Hi,

On 10.12.2021 12:36, 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).
>
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.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..2ff347da35c2 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);
>   }
>   
> +static int mtk_dsi_encoder_init(struct drm_device *drm, struct mtk_dsi *dsi)
> +{
> +	int ret;
> +
> +	ret = drm_simple_encoder_init(drm, &dsi->encoder,
> +				      DRM_MODE_ENCODER_DSI);
> +	if (ret) {
> +		DRM_ERROR("Failed to encoder init to drm\n");
> +		return ret;
> +	}
> +
> +	dsi->encoder.possible_crtcs = mtk_drm_find_possible_crtc_by_comp(drm, dsi->host.dev);
> +
> +	ret = drm_bridge_attach(&dsi->encoder, &dsi->bridge, NULL,
> +				DRM_BRIDGE_ATTACH_NO_CONNECTOR);
> +	if (ret)
> +		goto err_cleanup_encoder;
> +
> +	dsi->connector = drm_bridge_connector_init(drm, &dsi->encoder);
> +	if (IS_ERR(dsi->connector)) {
> +		DRM_ERROR("Unable to create bridge connector\n");
> +		ret = PTR_ERR(dsi->connector);
> +		goto err_cleanup_encoder;
> +	}
> +	drm_connector_attach_encoder(dsi->connector, &dsi->encoder);
> +
> +	return 0;
> +
> +err_cleanup_encoder:
> +	drm_encoder_cleanup(&dsi->encoder);
> +	return ret;
> +}
> +
> +static int mtk_dsi_bind(struct device *dev, struct device *master, void *data)
> +{
> +	int ret;
> +	struct drm_device *drm = data;
> +	struct mtk_dsi *dsi = dev_get_drvdata(dev);
> +
> +	ret = mtk_dsi_encoder_init(drm, dsi);
> +	if (ret)
> +		return ret;
> +
> +	return device_reset_optional(dev);
> +}
> +
> +static void mtk_dsi_unbind(struct device *dev, struct device *master,
> +			   void *data)
> +{
> +	struct mtk_dsi *dsi = dev_get_drvdata(dev);
> +
> +	drm_encoder_cleanup(&dsi->encoder);
> +}
> +
> +static const struct component_ops mtk_dsi_component_ops = {
> +	.bind = mtk_dsi_bind,
> +	.unbind = mtk_dsi_unbind,
> +};
> +
>   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);
> +	if (IS_ERR(dsi->next_bridge))
> +		return PTR_ERR(dsi->next_bridge);


Here we have implicit assumption that port node (0,0) points always to 
the 'device'. I guess it is true for now, but could bite someday. Anyway 
improving it  would require adding some additional helper for getting 
bridge based on mipi_dsi_device and should be done in separate patchset.


> +
> +	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);
> +
> +	drm_bridge_remove(&dsi->bridge);
> +	component_del(host->dev, &mtk_dsi_component_ops);


Order should be reversed.

With this fixed:

Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>


Regards

Andrzej


> +	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,
>   };
>   
> -static int mtk_dsi_encoder_init(struct drm_device *drm, struct mtk_dsi *dsi)
> -{
> -	int ret;
> -
> -	ret = drm_simple_encoder_init(drm, &dsi->encoder,
> -				      DRM_MODE_ENCODER_DSI);
> -	if (ret) {
> -		DRM_ERROR("Failed to encoder init to drm\n");
> -		return ret;
> -	}
> -
> -	dsi->encoder.possible_crtcs = mtk_drm_find_possible_crtc_by_comp(drm, dsi->host.dev);
> -
> -	ret = drm_bridge_attach(&dsi->encoder, &dsi->bridge, NULL,
> -				DRM_BRIDGE_ATTACH_NO_CONNECTOR);
> -	if (ret)
> -		goto err_cleanup_encoder;
> -
> -	dsi->connector = drm_bridge_connector_init(drm, &dsi->encoder);
> -	if (IS_ERR(dsi->connector)) {
> -		DRM_ERROR("Unable to create bridge connector\n");
> -		ret = PTR_ERR(dsi->connector);
> -		goto err_cleanup_encoder;
> -	}
> -	drm_connector_attach_encoder(dsi->connector, &dsi->encoder);
> -
> -	return 0;
> -
> -err_cleanup_encoder:
> -	drm_encoder_cleanup(&dsi->encoder);
> -	return ret;
> -}
> -
> -static int mtk_dsi_bind(struct device *dev, struct device *master, void *data)
> -{
> -	int ret;
> -	struct drm_device *drm = data;
> -	struct mtk_dsi *dsi = dev_get_drvdata(dev);
> -
> -	ret = mtk_dsi_encoder_init(drm, dsi);
> -	if (ret)
> -		return ret;
> -
> -	return device_reset_optional(dev);
> -}
> -
> -static void mtk_dsi_unbind(struct device *dev, struct device *master,
> -			   void *data)
> -{
> -	struct mtk_dsi *dsi = dev_get_drvdata(dev);
> -
> -	drm_encoder_cleanup(&dsi->encoder);
> -}
> -
> -static const struct component_ops mtk_dsi_component_ops = {
> -	.bind = mtk_dsi_bind,
> -	.unbind = mtk_dsi_unbind,
> -};
> -
>   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;