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Message-ID: <5da5b38f-1f34-4a1e-88a3-f7a90753e094@bootlin.com>
Date: Mon, 17 Nov 2025 14:12:17 +0000
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 RESEND v2 05/32] drm/vkms: Introduce config for plane name
On 11/13/25 14:17, José Expósito wrote:
> On Wed, Oct 29, 2025 at 03:36:42PM +0100, Louis Chauvet wrote:
>> As planes can have a name in DRM, prepare VKMS to configure it using
>> ConfigFS.
>>
>> Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
>> ---
>> drivers/gpu/drm/vkms/vkms_config.c | 4 ++++
>> drivers/gpu/drm/vkms/vkms_config.h | 26 ++++++++++++++++++++++++++
>> drivers/gpu/drm/vkms/vkms_drv.h | 5 +++--
>> drivers/gpu/drm/vkms/vkms_output.c | 6 +-----
>> drivers/gpu/drm/vkms/vkms_plane.c | 6 ++++--
>> 5 files changed, 38 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/vkms/vkms_config.c b/drivers/gpu/drm/vkms/vkms_config.c
>> index 858bec2d1312..bfafb5d2504d 100644
>> --- a/drivers/gpu/drm/vkms/vkms_config.c
>> +++ b/drivers/gpu/drm/vkms/vkms_config.c
>> @@ -352,6 +352,8 @@ static int vkms_config_show(struct seq_file *m, void *data)
>> seq_puts(m, "plane:\n");
>> seq_printf(m, "\ttype=%s\n",
>> drm_get_plane_type_name(vkms_config_plane_get_type(plane_cfg)));
>> + seq_printf(m, "\tname=%s\n",
>> + vkms_config_plane_get_name(plane_cfg));
>
> I discovered this while working on some basic IGT tests to validate
> your changes.
>
> I think that this triggers undefined behavior. printf() and friends
> expect a non NULL value for %s:
> https://stackoverflow.com/a/11589479
>
> In my Fedora system, this prints "name=(null)", instead of an empty
> string.
>
> The same happens with the ConfigFS API:
>
> $ cat /sys/kernel/config/vkms/test_plane_default_values/planes/plane0/name
> (null)
>
> We'd need to return in both places an empty string instead.
Good catch, I will fix for v3!
>> }
>>
>> vkms_config_for_each_crtc(vkmsdev->config, crtc_cfg) {
>> @@ -392,6 +394,7 @@ struct vkms_config_plane *vkms_config_create_plane(struct vkms_config *config)
>>
>> plane_cfg->config = config;
>> vkms_config_plane_set_type(plane_cfg, DRM_PLANE_TYPE_OVERLAY);
>> + vkms_config_plane_set_name(plane_cfg, NULL);
>> xa_init_flags(&plane_cfg->possible_crtcs, XA_FLAGS_ALLOC);
>>
>> list_add_tail(&plane_cfg->link, &config->planes);
>> @@ -404,6 +407,7 @@ void vkms_config_destroy_plane(struct vkms_config_plane *plane_cfg)
>> {
>> xa_destroy(&plane_cfg->possible_crtcs);
>> list_del(&plane_cfg->link);
>> + kfree_const(plane_cfg->name);
>> kfree(plane_cfg);
>> }
>> EXPORT_SYMBOL_IF_KUNIT(vkms_config_destroy_plane);
>> diff --git a/drivers/gpu/drm/vkms/vkms_config.h b/drivers/gpu/drm/vkms/vkms_config.h
>> index 4c8d668e7ef8..57342db5795a 100644
>> --- a/drivers/gpu/drm/vkms/vkms_config.h
>> +++ b/drivers/gpu/drm/vkms/vkms_config.h
>> @@ -35,6 +35,7 @@ struct vkms_config {
>> *
>> * @link: Link to the others planes in vkms_config
>> * @config: The vkms_config this plane belongs to
>> + * @name: Name of the plane
>> * @type: Type of the plane. The creator of configuration needs to ensures that
>> * at least one primary plane is present.
>> * @possible_crtcs: Array of CRTCs that can be used with this plane
>> @@ -47,6 +48,7 @@ struct vkms_config_plane {
>> struct list_head link;
>> struct vkms_config *config;
>>
>> + const char *name;
>> enum drm_plane_type type;
>> struct xarray possible_crtcs;
>>
>> @@ -288,6 +290,30 @@ vkms_config_plane_set_type(struct vkms_config_plane *plane_cfg,
>> plane_cfg->type = type;
>> }
>>
>> +/**
>> + * vkms_config_plane_set_name() - Set the plane name
>> + * @plane_cfg: Plane to set the name to
>> + * @name: New plane name. The name is copied.
>> + */
>> +static inline void
>> +vkms_config_plane_set_name(struct vkms_config_plane *plane_cfg,
>> + const char *name)
>> +{
>> + if (plane_cfg->name)
>> + kfree_const(plane_cfg->name);
>> + plane_cfg->name = kstrdup_const(name, GFP_KERNEL);
>> +}
>> +
>> +/**
>> + * vkms_config_plane_get_name - Get the plane name
>> + * @plane_cfg: Plane to get the name from
>> + */
>> +static inline const char *
>> +vkms_config_plane_get_name(const struct vkms_config_plane *plane_cfg)
>> +{
>> + return plane_cfg->name;
>> +}
>> +
>> /**
>> * vkms_config_plane_attach_crtc - Attach a plane to a CRTC
>> * @plane_cfg: Plane to attach
>> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
>> index db260df1d4f6..9ad286f043b5 100644
>> --- a/drivers/gpu/drm/vkms/vkms_drv.h
>> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
>> @@ -225,6 +225,7 @@ struct vkms_output {
>> };
>>
>> struct vkms_config;
>> +struct vkms_config_plane;
>>
>> /**
>> * struct vkms_device - Description of a VKMS device
>> @@ -298,10 +299,10 @@ int vkms_output_init(struct vkms_device *vkmsdev);
>> * vkms_plane_init() - Initialize a plane
>> *
>> * @vkmsdev: VKMS device containing the plane
>> - * @type: type of plane to initialize
>> + * @config: plane configuration
>> */
>> struct vkms_plane *vkms_plane_init(struct vkms_device *vkmsdev,
>> - enum drm_plane_type type);
>> + struct vkms_config_plane *config);
>>
>> /* CRC Support */
>> const char *const *vkms_get_crc_sources(struct drm_crtc *crtc,
>> diff --git a/drivers/gpu/drm/vkms/vkms_output.c b/drivers/gpu/drm/vkms/vkms_output.c
>> index 2ee3749e2b28..22208d02afa4 100644
>> --- a/drivers/gpu/drm/vkms/vkms_output.c
>> +++ b/drivers/gpu/drm/vkms/vkms_output.c
>> @@ -19,11 +19,7 @@ int vkms_output_init(struct vkms_device *vkmsdev)
>> return -EINVAL;
>>
>> vkms_config_for_each_plane(vkmsdev->config, plane_cfg) {
>> - enum drm_plane_type type;
>> -
>> - type = vkms_config_plane_get_type(plane_cfg);
>> -
>> - plane_cfg->plane = vkms_plane_init(vkmsdev, type);
>> + plane_cfg->plane = vkms_plane_init(vkmsdev, plane_cfg);
>> if (IS_ERR(plane_cfg->plane)) {
>> DRM_DEV_ERROR(dev->dev, "Failed to init vkms plane\n");
>> return PTR_ERR(plane_cfg->plane);
>> diff --git a/drivers/gpu/drm/vkms/vkms_plane.c b/drivers/gpu/drm/vkms/vkms_plane.c
>> index e592e47a5736..73180cbb78b1 100644
>> --- a/drivers/gpu/drm/vkms/vkms_plane.c
>> +++ b/drivers/gpu/drm/vkms/vkms_plane.c
>> @@ -9,6 +9,7 @@
>> #include <drm/drm_gem_atomic_helper.h>
>> #include <drm/drm_gem_framebuffer_helper.h>
>>
>> +#include "vkms_config.h"
>> #include "vkms_drv.h"
>> #include "vkms_formats.h"
>>
>> @@ -217,7 +218,7 @@ static const struct drm_plane_helper_funcs vkms_plane_helper_funcs = {
>> };
>>
>> struct vkms_plane *vkms_plane_init(struct vkms_device *vkmsdev,
>> - enum drm_plane_type type)
>> + struct vkms_config_plane *config)
>> {
>> struct drm_device *dev = &vkmsdev->drm;
>> struct vkms_plane *plane;
>> @@ -225,7 +226,8 @@ struct vkms_plane *vkms_plane_init(struct vkms_device *vkmsdev,
>> plane = drmm_universal_plane_alloc(dev, struct vkms_plane, base, 0,
>> &vkms_plane_funcs,
>> vkms_formats, ARRAY_SIZE(vkms_formats),
>> - NULL, type, NULL);
>> + NULL, vkms_config_plane_get_type(config),
>> + vkms_config_plane_get_name(config));
>> if (IS_ERR(plane))
>> return plane;
>>
>>
>> --
>> 2.51.0
>>
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