Message-Id: <DF1JDIS852IP.3JJPD06T65AB3@bootlin.com>
Date: Thu, 18 Dec 2025 18:59:07 +0100
From: "Luca Ceresoli" <luca.ceresoli@...tlin.com>
To: "Louis Chauvet" <louis.chauvet@...tlin.com>, "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>, <jose.exposito89@...il.com>, "Jonathan Corbet"
 <corbet@....net>
Cc: <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 RESEND v2 09/32] drm/vkms: Introduce configfs for plane
 rotation

On Wed Oct 29, 2025 at 3:36 PM CET, Louis Chauvet wrote:
> To allows the userspace to test many hardware configuration, introduce a
                                                configurations

> 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 | 91 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 97 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> index 1fe6e420c963..eac1a942d6c4 100644
> --- a/Documentation/gpu/vkms.rst
> +++ b/Documentation/gpu/vkms.rst
> @@ -87,11 +87,16 @@ Start by creating one or more planes::
>
>    sudo mkdir /config/vkms/my-vkms/planes/plane0
>
> -Planes have 2 configurable attributes:
> +Planes have 4 configurable attributes:
>
>  - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
>    exposed by the "type" property of a plane)
>  - name: Name of the 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 be6c3ba998b9..7cc8ba315ef0 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
> @@ -352,12 +352,103 @@ static ssize_t plane_name_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);

Small nit: below you do

  struct vkms_configfs_plane *plane = plane_item_to_vkms_configfs_plane(item);

Why not here as well?

> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		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)
> +			return -EINVAL;

The comment does not seem related to the code.

> +
> +		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);

Same as above.

> +
> +	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;

This if is redundant because...

> +	/* Should contains only one rotation */
        /* Should contain exactly one rotation */


> +	if (!is_power_of_2(val & DRM_MODE_ROTATE_MASK))
> +		return -EINVAL;

...is_power_of_2() returns false if the parameter is 0.

> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		/* Ensures that the default rotation is included in supported rotation */
> +		if (plane->dev->enabled)
> +			return -EINVAL;

Same as above.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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