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Message-ID: <aPuSKCNRGRCLDwyp@fedora>
Date: Fri, 24 Oct 2025 16:50:16 +0200
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 04/22] drm/vkms: Introduce configfs for plane rotation
On Sat, Oct 18, 2025 at 04:01:04AM +0200, Louis Chauvet wrote:
> To allows the userspace to test many hardware configuration, introduce a
> new interface to configure the available rotation per planes. VKMS
> supports any rotation and reflection, so the userspace can choose any
> combination.
>
> The supported rotations are configured by writing a rotation bitmask to
> the file `supported_rotations` and the default rotation is chosen by
> writing a rotation bitmask to `default_rotation`.
>
> Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> ---
> Documentation/gpu/vkms.rst | 7 ++-
> drivers/gpu/drm/vkms/vkms_configfs.c | 94 ++++++++++++++++++++++++++++++++++++
> 2 files changed, 100 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> index 3574e01b928d..a432968cc711 100644
> --- a/Documentation/gpu/vkms.rst
> +++ b/Documentation/gpu/vkms.rst
> @@ -87,10 +87,15 @@ Start by creating one or more planes::
>
> sudo mkdir /config/vkms/my-vkms/planes/plane0
>
> -Planes have 1 configurable attribute:
> +Planes have 3 configurable attribute:
s/attribute/attributes/
>
> - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
> exposed by the "type" property of a plane)
> +- possible_rotations: Available rotation for a plane, as a bitmask: 0x01 no rotation,
> + 0x02 rotate 90°, 0x04 rotate 180°, 0x08 rotate 270°, 0x10 reflect x, 0x20 reflect y
> + (same values as those exposed by the "rotation" property of a plane)
> +- default_rotation: Default rotation presented to the userspace, same values as
> + possible_rotations.
>
> Continue by creating one or more CRTCs::
>
> diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
> index ea245e2e2fd2..450e45e66a45 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
> @@ -322,10 +322,104 @@ static ssize_t plane_type_store(struct config_item *item, const char *page,
> return (ssize_t)count;
> }
>
> +static ssize_t plane_supported_rotations_show(struct config_item *item, char *page)
> +{
> + struct vkms_configfs_plane *plane;
> + unsigned int plane_supported_rotations;
> +
> + plane = plane_item_to_vkms_configfs_plane(item);
> +
> + scoped_guard(mutex, &plane->dev->lock) {
> + plane_supported_rotations = vkms_config_plane_get_supported_rotations(plane->config);
Checkpatch is complaining about this line being 1 character longer than
it should... Feel free to ignore it:
WARNING: line length of 101 exceeds 100 columns
#58: FILE: drivers/gpu/drm/vkms/vkms_configfs.c:333:
+ plane_supported_rotations = vkms_config_plane_get_supported_rotations(plane->config);
> + }
> +
> + return sprintf(page, "%u", plane_supported_rotations);
> +}
> +
> +static ssize_t plane_supported_rotations_store(struct config_item *item,
> + const char *page, size_t count)
> +{
> + struct vkms_configfs_plane *plane = plane_item_to_vkms_configfs_plane(item);
> + int ret, val = 0;
> +
> + ret = kstrtouint(page, 0, &val);
> + if (ret)
> + return ret;
> +
> + /* Should be a supported value */
> + if (val & ~(DRM_MODE_ROTATE_MASK | DRM_MODE_REFLECT_MASK))
> + return -EINVAL;
> + /* Should at least provide one rotation */
> + if (!(val & DRM_MODE_ROTATE_MASK))
> + return -EINVAL;
> +
> + scoped_guard(mutex, &plane->dev->lock) {
> + /* Ensures that the default rotation is included in supported rotation */
> + if (plane->dev->enabled ||
> + (val & vkms_config_plane_get_default_rotation(plane->config)) !=
> + vkms_config_plane_get_default_rotation(plane->config))
> + return -EINVAL;
This makes a bit difficult to change the default supported rotations.
By default, default rotation is DRM_MODE_ROTATE_0. If the user wants to set the
supported rotations to DRM_MODE_REFLECT_X | DRM_MODE_REFLECT_Y | DRM_MODE_ROTATE_90,
this will fail because the default rotation is not included in the new set of
supported rotations.
Therefore, the user would need to add DRM_MODE_ROTATE_0 (DRM_MODE_REFLECT_X |
DRM_MODE_REFLECT_Y | DRM_MODE_ROTATE_90 | DRM_MODE_ROTATE_0), change the default rotation
to DRM_MODE_ROTATE_90 and drop DRM_MODE_ROTATE_0 from the supported rotations.
To avoid this, I think we should check this before enabling the device instead,
in vkms_config_is_valid().
Also, having this logic as a helper called by vkms_config_is_valid() allows to
add a KUnit test to make sure all cases are covered.
What do you think?
> + vkms_config_plane_set_supported_rotations(plane->config, val);
> + }
> +
> + return count;
> +}
> +
> +static ssize_t plane_default_rotation_show(struct config_item *item, char *page)
> +{
> + struct vkms_configfs_plane *plane;
> + unsigned int plane_default_rotation;
> +
> + plane = plane_item_to_vkms_configfs_plane(item);
> +
> + scoped_guard(mutex, &plane->dev->lock) {
> + plane_default_rotation = vkms_config_plane_get_default_rotation(plane->config);
> + }
> +
> + return sprintf(page, "%u", plane_default_rotation);
> +}
> +
> +static ssize_t plane_default_rotation_store(struct config_item *item,
> + const char *page, size_t count)
> +{
> + struct vkms_configfs_plane *plane = plane_item_to_vkms_configfs_plane(item);
> + int ret, val = 0;
> +
> + ret = kstrtouint(page, 10, &val);
> + if (ret)
> + return ret;
> +
> + /* Should be a supported value */
> + if (val & ~(DRM_MODE_ROTATE_MASK | DRM_MODE_REFLECT_MASK))
> + return -EINVAL;
> + /* Should at least provide one rotation */
> + if ((val & DRM_MODE_ROTATE_MASK) == 0)
> + return -EINVAL;
> + /* Should contains only one rotation */
> + if (!is_power_of_2(val & DRM_MODE_ROTATE_MASK))
> + return -EINVAL;
> +
> + scoped_guard(mutex, &plane->dev->lock) {
> + /* Ensures that the default rotation is included in supported rotation */
> + if (plane->dev->enabled ||
> + (val & vkms_config_plane_get_supported_rotations(plane->config)) != val)
> + return -EINVAL;
> +
> + vkms_config_plane_set_default_rotation(plane->config, val);
> + }
> +
> + return count;
> +}
> +
> CONFIGFS_ATTR(plane_, type);
> +CONFIGFS_ATTR(plane_, supported_rotations);
> +CONFIGFS_ATTR(plane_, default_rotation);
>
> static struct configfs_attribute *plane_item_attrs[] = {
> &plane_attr_type,
> + &plane_attr_supported_rotations,
> + &plane_attr_default_rotation,
> NULL,
> };
>
>
> --
> 2.51.0
>
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