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Message-ID: <88099b50-3b19-4080-a241-d8caddbf06e9@bootlin.com>
Date: Mon, 27 Oct 2025 18:18:54 +0100
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: José Expósito <jose.exposito89@...il.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
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@...tlin.com>
>> ---
>
> 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
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