Re: [PATCH 19/22] drm/vkms: Introduce configfs for connector EDID
From: Louis Chauvet
Date: Mon Oct 27 2025 - 13:21:07 EST
Le 27/10/2025 à 11:16, José Expósito a écrit :
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@xxxxxxxxxxx>
---
Hey Louis,
I wasn't able to set the EDID, could you provide an example?
Your usage is good, I expect it to work
But I forgot one very important call, probably lost during my multiple
rebases: drm_connector_attach_edid_property
But you also need to call modetest to properly refresh the EDID property
(I don't know exactly how it works, but if I don't call modetest first,
drm_info does not see the EDID)
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
--
--
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com