Message-ID: <20241015132849.GA447702-robh@kernel.org>
Date: Tue, 15 Oct 2024 08:28:49 -0500
From: Rob Herring <robh@...nel.org>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: chunkuang.hu@...nel.org, krzysztof.kozlowski+dt@...aro.org,
	conor+dt@...nel.org, p.zabel@...gutronix.de, airlied@...il.com,
	daniel@...ll.ch, maarten.lankhorst@...ux.intel.com,
	mripard@...nel.org, tzimmermann@...e.de, matthias.bgg@...il.com,
	shawn.sung@...iatek.com, yu-chang.lee@...iatek.com,
	ck.hu@...iatek.com, jitao.shi@...iatek.com,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linux-mediatek@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, wenst@...omium.org,
	kernel@...labora.com, sui.jingfeng@...ux.dev, michael@...le.cc,
	sjoerd@...labora.com, Alexandre Mergnat <amergnat@...libre.com>,
	Michael Walle <mwalle@...nel.org>
Subject: Re: [PATCH v12 3/3] drm/mediatek: Implement OF graphs support for
 display paths

On Mon, Oct 14, 2024 at 10:51:48AM +0200, AngeloGioacchino Del Regno wrote:
> It is impossible to add each and every possible DDP path combination
> for each and every possible combination of SoC and board: right now,
> this driver hardcodes configuration for 10 SoCs and this is going to
> grow larger and larger, and with new hacks like the introduction of
> mtk_drm_route which is anyway not enough for all final routes as the
> DSI cannot be connected to MERGE if it's not a dual-DSI, or enabling
> DSC preventively doesn't work if the display doesn't support it, or
> others.
> 
> Since practically all display IPs in MediaTek SoCs support being
> interconnected with different instances of other, or the same, IPs
> or with different IPs and in different combinations, the final DDP
> pipeline is effectively a board specific configuration.
> 
> Implement OF graphs support to the mediatek-drm drivers, allowing to
> stop hardcoding the paths, and preventing this driver to get a huge
> amount of arrays for each board and SoC combination, also paving the
> way to share the same mtk_mmsys_driver_data between multiple SoCs,
> making it more straightforward to add support for new chips.
> 
> Note that the OVL_ADAPTOR software component driver needs relatively
> big changes in order to fully support OF Graphs (and more SoCs anyway)
> and such changes will come at a later time.
> As of now, the mtk_disp_ovl_adaptor driver takes the MERGE components
> (for example, on mt8195, merge 1 to 4) dynamically so, even though
> later updates to the ovl-adaptor driver will *not* require bindings
> changes, the merge1-4 will be temporarily omitted in the graph for the
> MT8195 SoC.
> 
> This means that an example graph for this SoC looks like:
> 
> mdp_rdma (0 ~ 7) -> padding (0 ~ 7) -> ethdr -> merge5
> 
> and the resulting path in this driver will be `ovl_adaptor -> merge5`
> 
> Later updates to the ovl adaptor will expand it to support more SoCs
> and, in turn, to also fully support graphs.
> 
> Reviewed-by: Alexandre Mergnat <amergnat@...libre.com>
> Tested-by: Alexandre Mergnat <amergnat@...libre.com>
> Acked-by: Sui Jingfeng <sui.jingfeng@...ux.dev>
> Tested-by: Michael Walle <mwalle@...nel.org> # on kontron-sbc-i1200
> Reviewed-by: CK Hu <ck.hu@...iatek.com>
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_disp_drv.h       |   1 +
>  .../gpu/drm/mediatek/mtk_disp_ovl_adaptor.c   |  43 ++-
>  drivers/gpu/drm/mediatek/mtk_dpi.c            |  21 +-
>  drivers/gpu/drm/mediatek/mtk_drm_drv.c        | 253 +++++++++++++++++-
>  drivers/gpu/drm/mediatek/mtk_drm_drv.h        |   2 +-
>  drivers/gpu/drm/mediatek/mtk_dsi.c            |  14 +-
>  6 files changed, 312 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_disp_drv.h b/drivers/gpu/drm/mediatek/mtk_disp_drv.h
> index 082ac18fe04a..94843974851f 100644
> --- a/drivers/gpu/drm/mediatek/mtk_disp_drv.h
> +++ b/drivers/gpu/drm/mediatek/mtk_disp_drv.h
> @@ -108,6 +108,7 @@ size_t mtk_ovl_get_num_formats(struct device *dev);
>  
>  void mtk_ovl_adaptor_add_comp(struct device *dev, struct mtk_mutex *mutex);
>  void mtk_ovl_adaptor_remove_comp(struct device *dev, struct mtk_mutex *mutex);
> +bool mtk_ovl_adaptor_is_comp_present(struct device_node *node);
>  void mtk_ovl_adaptor_connect(struct device *dev, struct device *mmsys_dev,
>  			     unsigned int next);
>  void mtk_ovl_adaptor_disconnect(struct device *dev, struct device *mmsys_dev,
> diff --git a/drivers/gpu/drm/mediatek/mtk_disp_ovl_adaptor.c b/drivers/gpu/drm/mediatek/mtk_disp_ovl_adaptor.c
> index c6768210b08b..4e064d3c97cc 100644
> --- a/drivers/gpu/drm/mediatek/mtk_disp_ovl_adaptor.c
> +++ b/drivers/gpu/drm/mediatek/mtk_disp_ovl_adaptor.c
> @@ -490,6 +490,41 @@ static int compare_of(struct device *dev, void *data)
>  	return dev->of_node == data;
>  }
>  
> +static int ovl_adaptor_of_get_ddp_comp_type(struct device_node *node,
> +					    enum mtk_ovl_adaptor_comp_type *ctype)
> +{
> +	const struct of_device_id *of_id = of_match_node(mtk_ovl_adaptor_comp_dt_ids, node);
> +
> +	if (!of_id)
> +		return -EINVAL;
> +
> +	*ctype = (enum mtk_ovl_adaptor_comp_type)((uintptr_t)of_id->data);
> +
> +	return 0;
> +}
> +
> +bool mtk_ovl_adaptor_is_comp_present(struct device_node *node)
> +{
> +	enum mtk_ovl_adaptor_comp_type type;
> +	int ret;
> +
> +	ret = ovl_adaptor_of_get_ddp_comp_type(node, &type);
> +	if (ret)
> +		return false;
> +
> +	if (type >= OVL_ADAPTOR_TYPE_NUM)
> +		return false;
> +
> +	/*
> +	 * In the context of mediatek-drm, ETHDR, MDP_RDMA and Padding are
> +	 * used exclusively by OVL Adaptor: if this component is not one of
> +	 * those, it's likely not an OVL Adaptor path.
> +	 */
> +	return type == OVL_ADAPTOR_TYPE_ETHDR ||
> +	       type == OVL_ADAPTOR_TYPE_MDP_RDMA ||
> +	       type == OVL_ADAPTOR_TYPE_PADDING;
> +}
> +
>  static int ovl_adaptor_comp_init(struct device *dev, struct component_match **match)
>  {
>  	struct mtk_disp_ovl_adaptor *priv = dev_get_drvdata(dev);
> @@ -499,12 +534,11 @@ static int ovl_adaptor_comp_init(struct device *dev, struct component_match **ma
>  	parent = dev->parent->parent->of_node->parent;
>  
>  	for_each_child_of_node_scoped(parent, node) {
> -		const struct of_device_id *of_id;
>  		enum mtk_ovl_adaptor_comp_type type;
> -		int id;
> +		int id, ret;
>  
> -		of_id = of_match_node(mtk_ovl_adaptor_comp_dt_ids, node);
> -		if (!of_id)
> +		ret = ovl_adaptor_of_get_ddp_comp_type(node, &type);
> +		if (ret)
>  			continue;
>  
>  		if (!of_device_is_available(node)) {
> @@ -513,7 +547,6 @@ static int ovl_adaptor_comp_init(struct device *dev, struct component_match **ma
>  			continue;
>  		}
>  
> -		type = (enum mtk_ovl_adaptor_comp_type)(uintptr_t)of_id->data;
>  		id = ovl_adaptor_comp_get_id(dev, node, type);
>  		if (id < 0) {
>  			dev_warn(dev, "Skipping unknown component %pOF\n",
> diff --git a/drivers/gpu/drm/mediatek/mtk_dpi.c b/drivers/gpu/drm/mediatek/mtk_dpi.c
> index e4da5cc75e60..ad37b0ecafb9 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dpi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dpi.c
> @@ -755,6 +755,20 @@ static int mtk_dpi_bridge_attach(struct drm_bridge *bridge,
>  				 enum drm_bridge_attach_flags flags)
>  {
>  	struct mtk_dpi *dpi = bridge_to_dpi(bridge);
> +	int ret;
> +
> +	dpi->next_bridge = devm_drm_of_get_bridge(dpi->dev, dpi->dev->of_node, 1, -1);
> +	if (IS_ERR(dpi->next_bridge)) {
> +		ret = PTR_ERR(dpi->next_bridge);
> +		if (ret == -EPROBE_DEFER)
> +			return ret;
> +
> +		/* Old devicetree has only one endpoint */
> +		dpi->next_bridge = devm_drm_of_get_bridge(dpi->dev, dpi->dev->of_node, 0, 0);
> +		if (IS_ERR(dpi->next_bridge))
> +			return dev_err_probe(dpi->dev, PTR_ERR(dpi->next_bridge),
> +					     "Failed to get bridge\n");
> +	}
>  
>  	return drm_bridge_attach(bridge->encoder, dpi->next_bridge,
>  				 &dpi->bridge, flags);
> @@ -1162,13 +1176,6 @@ static int mtk_dpi_probe(struct platform_device *pdev)
>  	if (dpi->irq < 0)
>  		return dpi->irq;
>  
> -	dpi->next_bridge = devm_drm_of_get_bridge(dev, dev->of_node, 0, 0);
> -	if (IS_ERR(dpi->next_bridge))
> -		return dev_err_probe(dev, PTR_ERR(dpi->next_bridge),
> -				     "Failed to get bridge\n");
> -
> -	dev_info(dev, "Found bridge node: %pOF\n", dpi->next_bridge->of_node);
> -
>  	platform_set_drvdata(pdev, dpi);
>  
>  	dpi->bridge.funcs = &mtk_dpi_bridge_funcs;
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> index a4594f8873d5..85be035a209a 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> @@ -27,6 +27,7 @@
>  
>  #include "mtk_crtc.h"
>  #include "mtk_ddp_comp.h"
> +#include "mtk_disp_drv.h"
>  #include "mtk_drm_drv.h"
>  #include "mtk_gem.h"
>  
> @@ -820,12 +821,235 @@ static const struct of_device_id mtk_ddp_comp_dt_ids[] = {
>  	{ }
>  };
>  
> +static int mtk_drm_of_get_ddp_comp_type(struct device_node *node, enum mtk_ddp_comp_type *ctype)
> +{
> +	const struct of_device_id *of_id = of_match_node(mtk_ddp_comp_dt_ids, node);
> +
> +	if (!of_id)
> +		return -EINVAL;
> +
> +	*ctype = (enum mtk_ddp_comp_type)((uintptr_t)of_id->data);
> +
> +	return 0;
> +}
> +
> +static int mtk_drm_of_get_ddp_ep_cid(struct device_node *node,
> +				     int output_port, enum mtk_crtc_path crtc_path,
> +				     struct device_node **next, unsigned int *cid)
> +{
> +	struct device_node *ep_dev_node, *ep_out;
> +	enum mtk_ddp_comp_type comp_type;
> +	int ret;
> +
> +	ep_out = of_graph_get_endpoint_by_regs(node, output_port, crtc_path);
> +	if (!ep_out)
> +		return -ENOENT;
> +
> +	ep_dev_node = of_graph_get_remote_port_parent(ep_out);
> +	of_node_put(ep_out);
> +	if (!ep_dev_node)
> +		return -EINVAL;
> +
> +	/*
> +	 * Pass the next node pointer regardless of failures in the later code
> +	 * so that if this function is called in a loop it will walk through all
> +	 * of the subsequent endpoints anyway.
> +	 */
> +	*next = ep_dev_node;
> +
> +	if (!of_device_is_available(ep_dev_node))
> +		return -ENODEV;
> +
> +	ret = mtk_drm_of_get_ddp_comp_type(ep_dev_node, &comp_type);
> +	if (ret) {
> +		if (mtk_ovl_adaptor_is_comp_present(ep_dev_node)) {
> +			*cid = (unsigned int)DDP_COMPONENT_DRM_OVL_ADAPTOR;
> +			return 0;
> +		}
> +		return ret;
> +	}
> +
> +	ret = mtk_ddp_comp_get_id(ep_dev_node, comp_type);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* All ok! Pass the Component ID to the caller. */
> +	*cid = (unsigned int)ret;
> +
> +	return 0;
> +}
> +
> +/**
> + * mtk_drm_of_ddp_path_build_one - Build a Display HW Pipeline for a CRTC Path
> + * @dev:          The mediatek-drm device
> + * @cpath:        CRTC Path relative to a VDO or MMSYS
> + * @out_path:     Pointer to an array that will contain the new pipeline
> + * @out_path_len: Number of entries in the pipeline array
> + *
> + * MediaTek SoCs can use different DDP hardware pipelines (or paths) depending
> + * on the board-specific desired display configuration; this function walks
> + * through all of the output endpoints starting from a VDO or MMSYS hardware
> + * instance and builds the right pipeline as specified in device trees.
> + *
> + * Return:
> + * * %0       - Display HW Pipeline successfully built and validated
> + * * %-ENOENT - Display pipeline was not specified in device tree
> + * * %-EINVAL - Display pipeline built but validation failed
> + * * %-ENOMEM - Failure to allocate pipeline array to pass to the caller
> + */
> +static int mtk_drm_of_ddp_path_build_one(struct device *dev, enum mtk_crtc_path cpath,
> +					 const unsigned int **out_path,
> +					 unsigned int *out_path_len)
> +{
> +	struct device_node *next, *prev, *vdo = dev->parent->of_node;
> +	unsigned int temp_path[DDP_COMPONENT_DRM_ID_MAX] = { 0 };
> +	unsigned int *final_ddp_path;
> +	unsigned short int idx = 0;
> +	bool ovl_adaptor_comp_added = false;
> +	int ret;
> +
> +	/* Get the first entry for the temp_path array */
> +	ret = mtk_drm_of_get_ddp_ep_cid(vdo, 0, cpath, &next, &temp_path[idx]);
> +	if (ret) {
> +		if (next && temp_path[idx] == DDP_COMPONENT_DRM_OVL_ADAPTOR) {
> +			dev_dbg(dev, "Adding OVL Adaptor for %pOF\n", next);
> +			ovl_adaptor_comp_added = true;
> +		} else {
> +			if (next)
> +				dev_err(dev, "Invalid component %pOF\n", next);
> +			else
> +				dev_err(dev, "Cannot find first endpoint for path %d\n", cpath);
> +
> +			return ret;
> +		}
> +	}
> +	idx++;
> +
> +	/*
> +	 * Walk through port outputs until we reach the last valid mediatek-drm component.
> +	 * To be valid, this must end with an "invalid" component that is a display node.
> +	 */
> +	do {
> +		prev = next;
> +		ret = mtk_drm_of_get_ddp_ep_cid(next, 1, cpath, &next, &temp_path[idx]);
> +		of_node_put(prev);
> +		if (ret) {
> +			of_node_put(next);
> +			break;
> +		}
> +
> +		/*
> +		 * If this is an OVL adaptor exclusive component and one of those
> +		 * was already added, don't add another instance of the generic
> +		 * DDP_COMPONENT_OVL_ADAPTOR, as this is used only to decide whether
> +		 * to probe that component master driver of which only one instance
> +		 * is needed and possible.
> +		 */
> +		if (temp_path[idx] == DDP_COMPONENT_DRM_OVL_ADAPTOR) {
> +			if (!ovl_adaptor_comp_added)
> +				ovl_adaptor_comp_added = true;
> +			else
> +				idx--;
> +		}
> +	} while (++idx < DDP_COMPONENT_DRM_ID_MAX);
> +
> +	/*
> +	 * The device component might not be enabled: in that case, don't
> +	 * check the last entry and just report that the device is missing.
> +	 */
> +	if (ret == -ENODEV)
> +		return ret;
> +
> +	/* If the last entry is not a final display output, the configuration is wrong */
> +	switch (temp_path[idx - 1]) {
> +	case DDP_COMPONENT_DP_INTF0:
> +	case DDP_COMPONENT_DP_INTF1:
> +	case DDP_COMPONENT_DPI0:
> +	case DDP_COMPONENT_DPI1:
> +	case DDP_COMPONENT_DSI0:
> +	case DDP_COMPONENT_DSI1:
> +	case DDP_COMPONENT_DSI2:
> +	case DDP_COMPONENT_DSI3:
> +		break;
> +	default:
> +		dev_err(dev, "Invalid display hw pipeline. Last component: %d (ret=%d)\n",
> +			temp_path[idx - 1], ret);
> +		return -EINVAL;
> +	}
> +
> +	final_ddp_path = devm_kmemdup(dev, temp_path, idx * sizeof(temp_path[0]), GFP_KERNEL);
> +	if (!final_ddp_path)
> +		return -ENOMEM;
> +
> +	dev_dbg(dev, "Display HW Pipeline built with %d components.\n", idx);
> +
> +	/* Pipeline built! */
> +	*out_path = final_ddp_path;
> +	*out_path_len = idx;
> +
> +	return 0;
> +}
> +
> +static int mtk_drm_of_ddp_path_build(struct device *dev, struct device_node *node,
> +				     struct mtk_mmsys_driver_data *data)
> +{
> +	struct device_node *ep_node;
> +	struct of_endpoint of_ep;
> +	bool output_present[MAX_CRTC] = { false };
> +	int ret;
> +
> +	for_each_endpoint_of_node(node, ep_node) {
> +		ret = of_graph_parse_endpoint(ep_node, &of_ep);
> +		if (ret) {
> +			dev_err_probe(dev, ret, "Cannot parse endpoint\n");
> +			break;
> +		}
> +
> +		if (of_ep.id >= MAX_CRTC) {
> +			ret = dev_err_probe(dev, -EINVAL,
> +					    "Invalid endpoint%u number\n", of_ep.port);
> +			break;
> +		}
> +
> +		output_present[of_ep.id] = true;
> +	}
> +
> +	if (ret) {
> +		of_node_put(ep_node);
> +		return ret;
> +	}
> +
> +	if (output_present[CRTC_MAIN]) {
> +		ret = mtk_drm_of_ddp_path_build_one(dev, CRTC_MAIN,
> +						    &data->main_path, &data->main_len);
> +		if (ret && ret != -ENODEV)
> +			return ret;
> +	}
> +
> +	if (output_present[CRTC_EXT]) {
> +		ret = mtk_drm_of_ddp_path_build_one(dev, CRTC_EXT,
> +						    &data->ext_path, &data->ext_len);
> +		if (ret && ret != -ENODEV)
> +			return ret;
> +	}
> +
> +	if (output_present[CRTC_THIRD]) {
> +		ret = mtk_drm_of_ddp_path_build_one(dev, CRTC_THIRD,
> +						    &data->third_path, &data->third_len);
> +		if (ret && ret != -ENODEV)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +
>  static int mtk_drm_probe(struct platform_device *pdev)
>  {
>  	struct device *dev = &pdev->dev;
>  	struct device_node *phandle = dev->parent->of_node;
>  	const struct of_device_id *of_id;
>  	struct mtk_drm_private *private;
> +	struct mtk_mmsys_driver_data *mtk_drm_data;
>  	struct device_node *node;
>  	struct component_match *match = NULL;
>  	struct platform_device *ovl_adaptor;
> @@ -846,7 +1070,27 @@ static int mtk_drm_probe(struct platform_device *pdev)
>  	if (!of_id)
>  		return -ENODEV;
>  
> -	private->data = of_id->data;
> +	mtk_drm_data = (struct mtk_mmsys_driver_data *)of_id->data;
> +	if (!mtk_drm_data)
> +		return -EINVAL;
> +
> +	/* Try to build the display pipeline from devicetree graphs */
> +	if (of_graph_is_present(phandle)) {
> +		dev_dbg(dev, "Building display pipeline for MMSYS %u\n",
> +			mtk_drm_data->mmsys_id);
> +		private->data = devm_kmemdup(dev, mtk_drm_data,
> +					     sizeof(*mtk_drm_data), GFP_KERNEL);
> +		if (!private->data)
> +			return -ENOMEM;
> +
> +		ret = mtk_drm_of_ddp_path_build(dev, phandle, private->data);
> +		if (ret)
> +			return ret;
> +	} else {
> +		/* No devicetree graphs support: go with hardcoded paths if present */
> +		dev_dbg(dev, "Using hardcoded paths for MMSYS %u\n", mtk_drm_data->mmsys_id);
> +		private->data = mtk_drm_data;
> +	};
>  
>  	private->all_drm_private = devm_kmalloc_array(dev, private->data->mmsys_dev_num,
>  						      sizeof(*private->all_drm_private),
> @@ -868,12 +1112,11 @@ static int mtk_drm_probe(struct platform_device *pdev)
>  
>  	/* Iterate over sibling DISP function blocks */
>  	for_each_child_of_node(phandle->parent, node) {
> -		const struct of_device_id *of_id;
>  		enum mtk_ddp_comp_type comp_type;
>  		int comp_id;
>  
> -		of_id = of_match_node(mtk_ddp_comp_dt_ids, node);
> -		if (!of_id)
> +		ret = mtk_drm_of_get_ddp_comp_type(node, &comp_type);
> +		if (ret)
>  			continue;
>  
>  		if (!of_device_is_available(node)) {
> @@ -882,8 +1125,6 @@ static int mtk_drm_probe(struct platform_device *pdev)
>  			continue;
>  		}
>  
> -		comp_type = (enum mtk_ddp_comp_type)(uintptr_t)of_id->data;
> -
>  		if (comp_type == MTK_DISP_MUTEX) {
>  			int id;
>  
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.h b/drivers/gpu/drm/mediatek/mtk_drm_drv.h
> index ce897984de51..675cdc90a440 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.h
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.h
> @@ -63,7 +63,7 @@ struct mtk_drm_private {
>  	struct device *mmsys_dev;
>  	struct device_node *comp_node[DDP_COMPONENT_DRM_ID_MAX];
>  	struct mtk_ddp_comp ddp_comp[DDP_COMPONENT_DRM_ID_MAX];
> -	const struct mtk_mmsys_driver_data *data;
> +	struct mtk_mmsys_driver_data *data;
>  	struct drm_atomic_state *suspend_state;
>  	unsigned int mbox_index;
>  	struct mtk_drm_private **all_drm_private;
> diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
> index eeec641cab60..33ceeb8d6925 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> @@ -988,9 +988,17 @@ static int mtk_dsi_host_attach(struct mipi_dsi_host *host,
>  	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);
> +	dsi->next_bridge = devm_drm_of_get_bridge(dev, dev->of_node, 1, 0);
> +	if (IS_ERR(dsi->next_bridge)) {
> +		ret = PTR_ERR(dsi->next_bridge);
> +		if (ret == -EPROBE_DEFER)
> +			return ret;
> +
> +		/* Old devicetree has only one endpoint */
> +		dsi->next_bridge = devm_drm_of_get_bridge(dev, dev->of_node, 0, 0);

Here's the problem with your binding change.

next_bridge was port 0, and now it is port 1. Yes, you have a fallback 
for an old DT, but what happens with a new DT passed to a kernel without 
the change here? 

Plus now we've got to carry this fallback code path when it's completely 
avoidable.

Rob

Powered by blists - more mailing lists