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    Subject[PATCH v2] drm/bridge: Add debugfs print for bridge chains
    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@f0000/i2c@20000000/dsi@e:toshiba,tc358778
    bridge[2] type: 0, ops: 0x3, OF: /bus@f0000/i2c@20010000/hdmi@48:lontium,lt8912b
    bridge[3] type: 11, ops: 0x7, OF: /hdmi-connector:hdmi-connector

    Signed-off-by: Tomi Valkeinen <tomi.valkeinen@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 | 50 +++++++++++++++++++++++++++++++++++++++++++
    drivers/gpu/drm/drm_debugfs.c | 3 +++
    include/drm/drm_bridge.h | 5 +++++
    3 files changed, 58 insertions(+)

    diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
    index c3d69af02e79..d3eb62d5ef3b 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 +1347,54 @@ 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);
    +
    + bridge = drm_bridge_chain_get_first_bridge(encoder);
    +
    + while (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++;
    + bridge = drm_bridge_get_next_bridge(bridge);
    + }
    + }
    +
    + return 0;
    +}
    +
    +/* any use in debugfs files to dump individual planes/crtc/etc? */
    +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@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 c90dbcffa0dc..3e89559d68cd 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>
    @@ -272,6 +273,8 @@ int drm_debugfs_init(struct drm_minor *minor, int minor_id,

    drm_debugfs_add_files(minor->dev, drm_debugfs_list, DRM_DEBUGFS_ENTRIES);

    + drm_bridge_debugfs_init(minor);
    +
    if (drm_drv_uses_atomic_modeset(dev)) {
    drm_atomic_debugfs_init(minor);
    }
    diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
    index bf964cdfb330..60dbee6bd1e6 100644
    --- a/include/drm/drm_bridge.h
    +++ b/include/drm/drm_bridge.h
    @@ -949,4 +949,9 @@ static inline struct drm_bridge *drmm_of_get_bridge(struct drm_device *drm,
    }
    #endif

    +#ifdef CONFIG_DEBUG_FS
    +struct drm_minor;
    +void drm_bridge_debugfs_init(struct drm_minor *minor);
    +#endif
    +
    #endif
    ---
    base-commit: c7a472297169156252a50d76965eb36b081186e2
    change-id: 20230721-drm-bridge-chain-debugfs-0bbc1522f57a
    Best regards,
    --
    Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>

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