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Message-ID: <aP9GawE3nY082QJs@fedora>
Date: Mon, 27 Oct 2025 11:16:11 +0100
From: José Expósito <jose.exposito89@...il.com>
To: Louis Chauvet <louis.chauvet@...tlin.com>
Cc: Haneen Mohammed <hamohammed.sa@...il.com>,
Simona Vetter <simona@...ll.ch>,
Melissa Wen <melissa.srw@...il.com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>, Jonathan Corbet <corbet@....net>,
victoria@...tem76.com, sebastian.wick@...hat.com,
thomas.petazzoni@...tlin.com, dri-devel@...ts.freedesktop.org,
linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH 19/22] drm/vkms: Introduce configfs for connector EDID
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@...tlin.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
>
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