Re: [PATCH v2 1/4] drm/simple-kms: Add drm_simple_encoder_{init, create}()

[Sam Ravnborg <sam@ravnborg.org>]

Hi Thomas.

On Tue, Feb 18, 2020 at 09:48:12AM +0100, Thomas Zimmermann wrote:
> This patch makes the internal encoder implementation of the simple
> KMS helpers available to drivers.
> 
> These simple-encoder helpers initialize an encoder with an empty
> implementation. This covers the requirements of most of the existing
> DRM drivers. A call to drm_simple_encoder_create() allocates and
> initializes an encoder instance, a call to drm_simple_encoder_init()
> initializes a pre-allocated instance.
> 
> v2:
> 	* move simple encoder to KMS helpers
> 	* remove name argument; simplifies implementation
> 	* don't allocate with devm_ interfaces; unsafe with DRM
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---
>  drivers/gpu/drm/drm_simple_kms_helper.c | 83 ++++++++++++++++++++++++-
>  include/drm/drm_simple_kms_helper.h     |  7 +++
>  2 files changed, 87 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_simple_kms_helper.c b/drivers/gpu/drm/drm_simple_kms_helper.c
> index 15fb516ae2d8..745c2f34c42b 100644
> --- a/drivers/gpu/drm/drm_simple_kms_helper.c
> +++ b/drivers/gpu/drm/drm_simple_kms_helper.c
> @@ -26,12 +26,90 @@
>   * entity. Some flexibility for code reuse is provided through a separately
>   * allocated &drm_connector object and supporting optional &drm_bridge
>   * encoder drivers.
> + *
> + * Many drivers use an encoder with an empty implementation. Such encoders
> + * fulfill the minimum requirements of the display pipeline, but don't add
> + * additional functionality. The simple-encoder functions
> + * drm_simple_encoder_init() and drm_simple_encoder_create() provide an
> + * appropriate implementation.
This paragraph reads a bit strange to me - I read this as a
justification for addding a generic encoded that can be used by exisitg
drivers.

How about something like this:

Many drivers requires a very simple encoder that only fullfill
the minimum requirements of the display pipeline and do not add
any extra functionslity.
The simple-encoder functions drm_simple_encoder_init() and
drm_simple_encoder_create() provides an impålmentation of such
a simple encoder.
The simple encoder includes automatically release of resources.

And then leave it to the changelog to tell what should be done in
existing drivers.



>   */
>  
> -static const struct drm_encoder_funcs drm_simple_kms_encoder_funcs = {
> +static const struct drm_encoder_funcs drm_simple_encoder_funcs_cleanup = {
>  	.destroy = drm_encoder_cleanup,
>  };
>  
> +/**
> + * drm_simple_encoder_init - Initialize a preallocated encoder
> + * @dev: drm device
> + * @funcs: callbacks for this encoder
> + * @encoder_type: user visible type of the encoder
> + *
> + * Initialises a preallocated encoder that has no further functionality. The
> + * encoder will be released automatically. Settings for possible CRTC and
> + * clones are left to their initial values. The encoder will be cleaned up
> + * automatically as part of the mode-setting cleanup.
> + *
> + * Also see drm_simple_encoder_create().
s/Also see/See also/??


> + *
> + * Returns:
> + * Zero on success, error code on failure.
> + */
> +int drm_simple_encoder_init(struct drm_device *dev,
> +			    struct drm_encoder *encoder,
> +			    int encoder_type)
> +{
> +	return drm_encoder_init(dev, encoder,
> +				&drm_simple_encoder_funcs_cleanup,
> +				encoder_type, NULL);
> +}
> +EXPORT_SYMBOL(drm_simple_encoder_init);
> +
> +static void drm_encoder_destroy(struct drm_encoder *encoder)
> +{
> +	drm_encoder_cleanup(encoder);
> +	kfree(encoder);
> +}
> +
> +static const struct drm_encoder_funcs drm_simple_encoder_funcs_destroy = {
> +	.destroy = drm_encoder_destroy,
> +};
> +
> +/**
> + * drm_simple_encoder_create - Allocate and initialize an encoder
> + * @dev: drm device
> + * @encoder_type: user visible type of the encoder
> + *
> + * Allocates and initialises an encoder that has no further functionality. The
> + * encoder will be destroyed automatically as part of the mode-setting cleanup.
> + *
> + * See drm_simple_encoder_init() for more information.
> + *
> + * Returns:
> + * The encoder on success, a pointer-encoder error code on failure.
                                pointer-encoded?



> + */
> +struct drm_encoder *drm_simple_encoder_create(struct drm_device *dev,
> +					      int encoder_type)
> +{
> +	struct drm_encoder *encoder;
> +	int ret;
> +
> +	encoder = kzalloc(sizeof(*encoder), GFP_KERNEL);
> +	if (!encoder)
> +		return ERR_PTR(-ENOMEM);
> +	ret = drm_encoder_init(dev, encoder,
> +			       &drm_simple_encoder_funcs_destroy,
> +			       encoder_type, NULL);
> +	if (ret)
> +		goto err_kfree;
> +
> +	return encoder;
> +
> +err_kfree:
> +	kfree(encoder);
> +	return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL(drm_simple_encoder_create);
> +
>  static enum drm_mode_status
>  drm_simple_kms_crtc_mode_valid(struct drm_crtc *crtc,
>  			       const struct drm_display_mode *mode)
> @@ -288,8 +366,7 @@ int drm_simple_display_pipe_init(struct drm_device *dev,
>  		return ret;
>  
>  	encoder->possible_crtcs = drm_crtc_mask(crtc);
> -	ret = drm_encoder_init(dev, encoder, &drm_simple_kms_encoder_funcs,
> -			       DRM_MODE_ENCODER_NONE, NULL);
> +	ret = drm_simple_encoder_init(dev, encoder, DRM_MODE_ENCODER_NONE);
>  	if (ret || !connector)
>  		return ret;
>  
> diff --git a/include/drm/drm_simple_kms_helper.h b/include/drm/drm_simple_kms_helper.h
> index e253ba7bea9d..54d5066d90c7 100644
> --- a/include/drm/drm_simple_kms_helper.h
> +++ b/include/drm/drm_simple_kms_helper.h
> @@ -181,4 +181,11 @@ int drm_simple_display_pipe_init(struct drm_device *dev,
>  			const uint64_t *format_modifiers,
>  			struct drm_connector *connector);
>  
> +int drm_simple_encoder_init(struct drm_device *dev,
> +			    struct drm_encoder *encoder,
> +			    int encoder_type);
> +
> +struct drm_encoder *drm_simple_encoder_create(struct drm_device *dev,
> +					      int encoder_type);
> +
>  #endif /* __LINUX_DRM_SIMPLE_KMS_HELPER_H */

	Sam