[PATCH v4] drm/bridge: Add debugfs print for bridge chains

[Neil Armstrong]

On 02/08/2023 09:04, Tomi Valkeinen wrote:
> DRM bridges are not visible to the userspace and it may not be
> immediately clear if the chain is somehow constructed incorrectly. I
> have had two separate instances of a bridge driver failing to do a
> drm_bridge_attach() call, resulting in the bridge connector not being
> part of the chain. In some situations this doesn't seem to cause issues,
> but it will if DRM_BRIDGE_ATTACH_NO_CONNECTOR flag is used.
> 
> Add a debugfs file to print the bridge chains. For me, on this TI AM62
> based platform, I get the following output:
> 
> encoder[39]
> 	bridge[0] type: 0, ops: 0x0
> 	bridge[1] type: 0, ops: 0x0, OF: /bus at f0000/i2c at 20000000/dsi at e:toshiba,tc358778
> 	bridge[2] type: 0, ops: 0x3, OF: /bus at f0000/i2c at 20010000/hdmi at 48:lontium,lt8912b
> 	bridge[3] type: 11, ops: 0x7, OF: /hdmi-connector:hdmi-connector
> 
> Tested-by: Alexander Stein <alexander.stein at ew.tq-group.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas at ideasonboard.com>
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>
> ---
> Changes in v4:
> - Move 'struct drm_minor' to be along the other declarations
> - Added Tested-by and Reviewed-by
> - Link to v3: https://lore.kernel.org/r/20230731-drm-bridge-chain-debugfs-v3-1-7d0739f3efa3@ideasonboard.com
> 
> Changes in v3:
> - Use drm_for_each_bridge_in_chain()
> - Drop extra comment
> - Fix whitespace issue
> - Call drm_bridge_debugfs_init() only if the driver uses modeset
> - Drop #ifdef for drm_bridge_debugfs_init() declaration
> - Link to v2: https://lore.kernel.org/r/20230721-drm-bridge-chain-debugfs-v2-1-76df94347962@ideasonboard.com
> 
> Changes in v2:
> - Fixed compilation issue when !CONFIG_OF
> - Link to v1: https://lore.kernel.org/r/20230721-drm-bridge-chain-debugfs-v1-1-8614ff7e890d@ideasonboard.com
> ---
>   drivers/gpu/drm/drm_bridge.c  | 46 +++++++++++++++++++++++++++++++++++++++++++
>   drivers/gpu/drm/drm_debugfs.c |  2 ++
>   include/drm/drm_bridge.h      |  3 +++
>   3 files changed, 51 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index c3d69af02e79..39e68e45bb12 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -27,8 +27,10 @@
>   #include <linux/mutex.h>
>   
>   #include <drm/drm_atomic_state_helper.h>
> +#include <drm/drm_debugfs.h>
>   #include <drm/drm_bridge.h>
>   #include <drm/drm_encoder.h>
> +#include <drm/drm_file.h>
>   #include <drm/drm_of.h>
>   #include <drm/drm_print.h>
>   
> @@ -1345,6 +1347,50 @@ struct drm_bridge *of_drm_find_bridge(struct device_node *np)
>   EXPORT_SYMBOL(of_drm_find_bridge);
>   #endif
>   
> +#ifdef CONFIG_DEBUG_FS
> +static int drm_bridge_chains_info(struct seq_file *m, void *data)
> +{
> +	struct drm_debugfs_entry *entry = m->private;
> +	struct drm_device *dev = entry->dev;
> +	struct drm_printer p = drm_seq_file_printer(m);
> +	struct drm_mode_config *config = &dev->mode_config;
> +	struct drm_encoder *encoder;
> +	unsigned int bridge_idx = 0;
> +
> +	list_for_each_entry(encoder, &config->encoder_list, head) {
> +		struct drm_bridge *bridge;
> +
> +		drm_printf(&p, "encoder[%u]\n", encoder->base.id);
> +
> +		drm_for_each_bridge_in_chain(encoder, bridge) {
> +			drm_printf(&p, "\tbridge[%u] type: %u, ops: %#x",
> +				   bridge_idx, bridge->type, bridge->ops);
> +
> +#ifdef CONFIG_OF
> +			if (bridge->of_node)
> +				drm_printf(&p, ", OF: %pOFfc", bridge->of_node);
> +#endif
> +
> +			drm_printf(&p, "\n");
> +
> +			bridge_idx++;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct drm_debugfs_info drm_bridge_debugfs_list[] = {
> +	{ "bridge_chains", drm_bridge_chains_info, 0 },
> +};
> +
> +void drm_bridge_debugfs_init(struct drm_minor *minor)
> +{
> +	drm_debugfs_add_files(minor->dev, drm_bridge_debugfs_list,
> +			      ARRAY_SIZE(drm_bridge_debugfs_list));
> +}
> +#endif
> +
>   MODULE_AUTHOR("Ajay Kumar <ajaykumar.rs at samsung.com>");
>   MODULE_DESCRIPTION("DRM bridge infrastructure");
>   MODULE_LICENSE("GPL and additional rights");
> diff --git a/drivers/gpu/drm/drm_debugfs.c b/drivers/gpu/drm/drm_debugfs.c
> index a3a488205009..2de43ff3ce0a 100644
> --- a/drivers/gpu/drm/drm_debugfs.c
> +++ b/drivers/gpu/drm/drm_debugfs.c
> @@ -31,6 +31,7 @@
>   
>   #include <drm/drm_atomic.h>
>   #include <drm/drm_auth.h>
> +#include <drm/drm_bridge.h>
>   #include <drm/drm_client.h>
>   #include <drm/drm_debugfs.h>
>   #include <drm/drm_device.h>
> @@ -274,6 +275,7 @@ int drm_debugfs_init(struct drm_minor *minor, int minor_id,
>   
>   	if (drm_drv_uses_atomic_modeset(dev)) {
>   		drm_atomic_debugfs_init(minor);
> +		drm_bridge_debugfs_init(minor);
>   	}
>   
>   	if (drm_core_check_feature(dev, DRIVER_MODESET)) {
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index bf964cdfb330..c339fc85fd07 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -36,6 +36,7 @@ struct drm_bridge;
>   struct drm_bridge_timings;
>   struct drm_connector;
>   struct drm_display_info;
> +struct drm_minor;
>   struct drm_panel;
>   struct edid;
>   struct i2c_adapter;
> @@ -949,4 +950,6 @@ static inline struct drm_bridge *drmm_of_get_bridge(struct drm_device *drm,
>   }
>   #endif
>   
> +void drm_bridge_debugfs_init(struct drm_minor *minor);
> +
>   #endif
> 
> ---
> base-commit: a0c64d153d687756c8719b8d10e609d62e1cb6fd
> change-id: 20230721-drm-bridge-chain-debugfs-0bbc1522f57a
> 
> Best regards,

LGTM, thanks tomi !

Acked-by: Neil Armstrong <neil.armstrong at linaro.org>