linux-kernel - Re: [PATCH v2 08/15] drm/vkms: Add a validation function for VKMS configuration

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Message-ID: <Z6362KrzjLUL6Mj6@louis-chauvet-laptop>
Date: Thu, 13 Feb 2025 14:59:52 +0100
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: José Expósito <jose.exposito89@...il.com>
Cc: hamohammed.sa@...il.com, simona@...ll.ch, melissa.srw@...il.com,
	maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
	tzimmermann@...e.de, airlied@...il.com,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 08/15] drm/vkms: Add a validation function for VKMS
 configuration

On 11/02/25 - 12:09, José Expósito wrote:
> From: Louis Chauvet <louis.chauvet@...tlin.com>
> 
> As the configuration will be used by userspace, add a validator to avoid
> creating a broken DRM device.
> 
> For the moment, the function always returns true, but rules will be
> added in future patches.
> 
> Reviewed-by: Louis Chauvet <louis.chauvet@...tlin.com>
> Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> Co-developed-by: José Expósito <jose.exposito89@...il.com>
> Signed-off-by: José Expósito <jose.exposito89@...il.com>

The compilation is broken when building as module:


diff --git a/drivers/gpu/drm/vkms/vkms_config.c b/drivers/gpu/drm/vkms/vkms_config.c
index b9267aef4804..82335006c94a 100644
--- a/drivers/gpu/drm/vkms/vkms_config.c
+++ b/drivers/gpu/drm/vkms/vkms_config.c
@@ -55,6 +55,7 @@ bool vkms_config_is_valid(struct vkms_config *config)
 {
        return true;
 }
+EXPORT_SYMBOL_IF_KUNIT(vkms_config_is_valid);

 static int vkms_config_show(struct seq_file *m, void *data)
 {


> ---
>  drivers/gpu/drm/vkms/tests/vkms_config_test.c |  2 ++
>  drivers/gpu/drm/vkms/vkms_config.c            |  5 +++++
>  drivers/gpu/drm/vkms/vkms_config.h            | 10 ++++++++++
>  drivers/gpu/drm/vkms/vkms_drv.h               |  2 +-
>  drivers/gpu/drm/vkms/vkms_output.c            |  3 +++
>  5 files changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/vkms/tests/vkms_config_test.c b/drivers/gpu/drm/vkms/tests/vkms_config_test.c
> index 92798590051b..6e07139d261c 100644
> --- a/drivers/gpu/drm/vkms/tests/vkms_config_test.c
> +++ b/drivers/gpu/drm/vkms/tests/vkms_config_test.c
> @@ -54,6 +54,8 @@ static void vkms_config_test_default_config(struct kunit *test)
>  	KUNIT_EXPECT_EQ(test, config->writeback, params->enable_writeback);
>  	KUNIT_EXPECT_EQ(test, config->overlay, params->enable_overlay);
>  
> +	KUNIT_EXPECT_TRUE(test, vkms_config_is_valid(config));
> +
>  	vkms_config_destroy(config);
>  }
>  
> diff --git a/drivers/gpu/drm/vkms/vkms_config.c b/drivers/gpu/drm/vkms/vkms_config.c
> index 11b0e539920b..67f71d29596e 100644
> --- a/drivers/gpu/drm/vkms/vkms_config.c
> +++ b/drivers/gpu/drm/vkms/vkms_config.c
> @@ -47,6 +47,11 @@ void vkms_config_destroy(struct vkms_config *config)
>  	kfree(config);
>  }
>  
> +bool vkms_config_is_valid(struct vkms_config *config)
> +{
> +	return true;
> +}
> +
>  static int vkms_config_show(struct seq_file *m, void *data)
>  {
>  	struct drm_debugfs_entry *entry = m->private;
> diff --git a/drivers/gpu/drm/vkms/vkms_config.h b/drivers/gpu/drm/vkms/vkms_config.h
> index fcaa909fb2e0..0376dceaf6be 100644
> --- a/drivers/gpu/drm/vkms/vkms_config.h
> +++ b/drivers/gpu/drm/vkms/vkms_config.h
> @@ -67,6 +67,16 @@ vkms_config_get_device_name(struct vkms_config *config)
>  	return config->dev_name;
>  }
>  
> +/**
> + * vkms_config_is_valid() - Validate a configuration
> + * @config: Configuration to validate
> + *
> + * Returns:
> + * Whether the configuration is valid or not.
> + * For example, a configuration without primary planes is not valid.
> + */
> +bool vkms_config_is_valid(struct vkms_config *config);
> +

I think here we can take a const pointer.

>  /**
>   * vkms_config_register_debugfs() - Register a debugfs file to show the device's
>   * configuration
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index a74a7fc3a056..95afc39ce985 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -204,7 +204,7 @@ struct vkms_config;
>  struct vkms_device {
>  	struct drm_device drm;
>  	struct platform_device *platform;
> -	const struct vkms_config *config;
> +	struct vkms_config *config;

So we can keep a const pointer here (for me the device should never modify 
vkms_config)

>  };
>  
>  /*
> diff --git a/drivers/gpu/drm/vkms/vkms_output.c b/drivers/gpu/drm/vkms/vkms_output.c
> index 068a7f87ecec..414cc933af41 100644
> --- a/drivers/gpu/drm/vkms/vkms_output.c
> +++ b/drivers/gpu/drm/vkms/vkms_output.c
> @@ -16,6 +16,9 @@ int vkms_output_init(struct vkms_device *vkmsdev)
>  	int writeback;
>  	unsigned int n;
>  
> +	if (!vkms_config_is_valid(vkmsdev->config))
> +		return -EINVAL;
> +
>  	/*
>  	 * Initialize used plane. One primary plane is required to perform the composition.
>  	 *
> -- 
> 2.48.1
>