Re: [PATCH 19/22] drm/vkms: Introduce configfs for connector EDID

["José Expósito" <jose.exposito89@gmail.com>]

On Sat, Oct 18, 2025 at 04:01:19AM +0200, Louis Chauvet wrote:
> Introduce new attributes to configure EDID of a connector:
> - edid_enable - chose if the connector will have an EDD or not
> - edid - raw edid content
> 
> Due to limitation of ConfigFS, the max len of EDID is PAGE_SIZE (4kB on
> x86), it should be sufficient for many tests. One possible evolution is
> using a ConfigFS blob to allow bigger EDID.
> 
> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> ---

Hey Louis,

I wasn't able to set the EDID, could you provide an example?

This is what I tried:

# I'm using QEMU's EDID:
$ cat /sys/class/drm/card0-Virtual-1/edid > qemu-edid.bin

# Create a simple device:
$ sudo mkdir /sys/kernel/config/vkms/gpu1 && \
sudo mkdir /sys/kernel/config/vkms/gpu1/planes/plane0  && \
echo "1" | sudo tee /sys/kernel/config/vkms/gpu1/planes/plane0/type && \
sudo mkdir /sys/kernel/config/vkms/gpu1/crtcs/crtc0 && \
echo "0" | sudo tee /sys/kernel/config/vkms/gpu1/crtcs/crtc0/writeback && \
sudo mkdir /sys/kernel/config/vkms/gpu1/encoders/encoder0 && \
sudo mkdir /sys/kernel/config/vkms/gpu1/connectors/connector0 && \
sudo ln -s /sys/kernel/config/vkms/gpu1/crtcs/crtc0 /sys/kernel/config/vkms/gpu1/planes/plane0/possible_crtcs && \
sudo ln -s /sys/kernel/config/vkms/gpu1/crtcs/crtc0 /sys/kernel/config/vkms/gpu1/encoders/encoder0/possible_crtcs && \
sudo ln -s /sys/kernel/config/vkms/gpu1/encoders/encoder0 /sys/kernel/config/vkms/gpu1/connectors/connector0/possible_encoders

$ cat qemu-edid.bin | sudo tee /sys/kernel/config/vkms/gpu1/connectors/connector0/edid

# The EDID is stored and it is correct:
$ cat /sys/kernel/config/vkms/gpu1/connectors/connector0/edid | edid-decode

$ echo "1" | sudo tee /sys/kernel/config/vkms/gpu1/connectors/connector0/edid_enabled
$ echo "1" | sudo tee /sys/kernel/config/vkms/gpu1/enabled

# After enabling the device, the EDID is not present:
$ cat /sys/class/drm/card1-Virtual-2/edid
<empty>

And drm_info does not show the EDID property.

Am I missing something?

>  Documentation/gpu/vkms.rst           |  5 ++-
>  drivers/gpu/drm/vkms/vkms_configfs.c | 81 +++++++++++++++++++++++++++++++++++-
>  2 files changed, 84 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> index 650d6f6e79fd..bbd03f61e61c 100644
> --- a/Documentation/gpu/vkms.rst
> +++ b/Documentation/gpu/vkms.rst
> @@ -135,7 +135,7 @@ Last but not least, create one or more connectors::
>  
>    sudo mkdir /config/vkms/my-vkms/connectors/connector0
>  
> -Connectors have 3 configurable attribute:
> +Connectors have 5 configurable attribute:
>  
>  - status: Connection status: 1 connected, 2 disconnected, 3 unknown (same values
>    as those exposed by the "status" property of a connector)
> @@ -144,6 +144,9 @@ Connectors have 3 configurable attribute:
>    If supported_colorspaces is not 0, the HDR_OUTPUT_METADATA will also be created.
>    Value is a bitfield, 0x1 = NO_DATA, 0x2 = SMPTE_170M_YCC... see enum drm_colorspace
>    for full list.
> +- edid_enabled: Enable or not EDID for this connector. Some connectors may not have an
> +  EDID but just a list of modes, this attribute allows to disable EDID property.
> +- edid: Content of the EDID. Ignored if edid_enabled is not set
>  
>  
>  To finish the configuration, link the different pipeline items::
> diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
> index 909f4557caec..a977c0842cd6 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
> @@ -1,5 +1,4 @@
>  // SPDX-License-Identifier: GPL-2.0+
> -#include "asm-generic/errno-base.h"
>  #include <linux/cleanup.h>
>  #include <linux/configfs.h>
>  #include <linux/mutex.h>
> @@ -1222,14 +1221,94 @@ static ssize_t connector_supported_colorspaces_store(struct config_item *item,
>  	return count;
>  }
>  
> +static ssize_t connector_edid_enabled_show(struct config_item *item, char *page)
> +{
> +	struct vkms_configfs_connector *connector;
> +	bool enabled;
> +
> +	connector = connector_item_to_vkms_configfs_connector(item);
> +
> +	scoped_guard(mutex, &connector->dev->lock)
> +		enabled = vkms_config_connector_get_edid_enabled(connector->config);
> +
> +	return sprintf(page, "%d\n", enabled);
> +}
> +
> +static ssize_t connector_edid_enabled_store(struct config_item *item,
> +					    const char *page, size_t count)
> +{
> +	struct vkms_configfs_connector *connector;
> +	struct vkms_config_connector *connector_cfg;
> +	bool enabled;
> +
> +	connector = connector_item_to_vkms_configfs_connector(item);
> +	connector_cfg = connector->config;
> +
> +	if (kstrtobool(page, &enabled))
> +		return -EINVAL;
> +
> +	scoped_guard(mutex, &connector->dev->lock)
> +	{
> +		vkms_config_connector_set_edid_enabled(connector_cfg, enabled);
> +
> +		if (connector->dev->enabled &&
> +		    vkms_config_connector_get_status(connector_cfg) !=
> +		    connector_status_disconnected)
> +			vkms_trigger_connector_hotplug(connector->dev->config->dev);
> +	}
> +	return count;
> +}
> +
> +static ssize_t connector_edid_show(struct config_item *item, char *page)
> +{
> +	struct vkms_configfs_connector *connector;
> +
> +	connector = connector_item_to_vkms_configfs_connector(item);
> +
> +	scoped_guard(mutex, &connector->dev->lock)
> +	{
> +		unsigned int len = 0;
> +		const u8 *edid = vkms_config_connector_get_edid(connector->config, &len);
> +
> +		memcpy(page, edid, min(len, PAGE_SIZE));
> +		return min(len, PAGE_SIZE);
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static ssize_t connector_edid_store(struct config_item *item,
> +				    const char *page, size_t count)
> +{
> +	struct vkms_configfs_connector *connector;
> +
> +	connector = connector_item_to_vkms_configfs_connector(item);
> +
> +	scoped_guard(mutex, &connector->dev->lock)
> +	{
> +		vkms_config_connector_set_edid(connector->config, page, count);
> +
> +		if (connector->dev->enabled &&
> +		    vkms_config_connector_get_status(connector->config) !=
> +		    connector_status_disconnected)
> +			vkms_trigger_connector_hotplug(connector->dev->config->dev);
> +	}
> +
> +	return count;
> +}
> +
>  CONFIGFS_ATTR(connector_, status);
>  CONFIGFS_ATTR(connector_, type);
>  CONFIGFS_ATTR(connector_, supported_colorspaces);
> +CONFIGFS_ATTR(connector_, edid_enabled);
> +CONFIGFS_ATTR(connector_, edid);
>  
>  static struct configfs_attribute *connector_item_attrs[] = {
>  	&connector_attr_status,
>  	&connector_attr_type,
>  	&connector_attr_supported_colorspaces,
> +	&connector_attr_edid_enabled,
> +	&connector_attr_edid,
>  	NULL,
>  };
>  
> 
> -- 
> 2.51.0
>